Basic Exterior
Wood Restoration
BEFORE WE GET STARTED
The primary focus of this seminar is QUALITY. The secondary focus is PROFITABILITY. This manual is
part of a class designed to set you apart as a wood care professional. In this material we will spend
considerable time on techniques, tools, materials, etc. with the intention of teaching you the most effective
way to operate. We will never teach you to sacrifice quality for profit, and we will always demonstrate the
least expensive way to achieve customer satisfaction.
This manual was written by successful contractors to help you become a successful contractor. This
material has been critiqued and approved by several groups to make sure it presents the best information in
the best possible way.
A test is available for certification. Any contractor may become a Contractors Foundation certified Contractor
by taking and passing this test – whether or not you take the class. The class, and this manual, are study
guides to make sure you are exposed to the correct way to restore decks and all wood exposed to nature.
If you are taking a class with us today, the test will be available to you immediately following the class.
© 1999 - 2010, Contractors Foundation
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CERTIFICATION STANDARDS
A Contractors Foundation Certified Contractor must always meet exceedingly high ethics and standards in
order to remain certified. This course is designed to teach you the recognized methods and procedures. We
encourage you to develop good work habits based on what you learn here.
1. Always work safely. Keep the safety of you, your employees, and your customers foremost in your
execution of the job. Concentrate on the prevention of slips and falls and chemical handling safety.
Regularly inspect ladders and other equipment to prevent unsafe conditions on the job. A Certified
Contractor always provides a safe working environment.
2. Use care with wood. Use the lowest pressure necessary to complete job. Use wood-cleaning chemicals
conservatively, just strong enough to accomplish the task. A Certified Contractor minimizes damage to the
wood and maximizes its life.
3. Protect the environment. Clean up spills immediately. Prevent damage to the customer’s property,
plants and animals near your work. A Certified Contractor is vigilant about protecting the environment in the
workplace.
4. Use ethical business practices. Educate your customer about the products you intend to use. Be
realistic about product performance. A Certified Contractor always charges a fair price for his work,
completes the job within a reasonable time, and guarantees the quality of his workmanship.
5. Follow the techniques listed in this manual. Establish consistent work habits when cleaning,
brightening (neutralizing), and sealing wood. A Certified Contractor always prepares wood properly before
sealing and always applies products according to the manufacturer’s directions.
6. Display your credentials. A Certified Contractor is proud of his education, knowledge, and high
standards. He/she proudly displays the Wood Certification wherever practical.
7. Continued education. A Certified Contractor stays abreast of all changes in the industry by maintaining
updates and re-certifying every three years.
8. Professionalism/Courtesy/Image. A Certified Contractor keeps vehicles, equipment and attire clean. It
is important to keep the job site as convenient as possible therefore keep equipment picked up and vehicles
out of the way as not to further inconvenience the customer.
© 1999 - 2010, Contractors Foundation
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THE BEGINNING
Is there a Market for our services? The answer is a resounding “YES” !
Have you observed how much exposed wood is
around you? Take a moment and look around.
Everywhere you look you see unprotected wood.
All across America, 1 out of every 3 homes has a
wood deck. Decks are one of today’s most
popular home improvement projects. Besides
adding extra room to a house, they are a proven
addition to its value. When selling their home,
homeowners recoup 73% - 110% of the cost of
adding a deck. According to the National
Association of Home Builders (NAHB), the cost of
building a deck can range from under $1,000 for a
small, simple structure, to more than $30,000 for
a large, custom design.
Wood of all kinds - redwood, cedar, pine, ipe,
cypress, mahogany, and more are being used on
the outside of homes. Decks, fences, docks, play sets, cedar roofs, and cedar siding are everywhere. These
are our opportunities!
All of this wood is turning gray and rotting away. Even the painted wood is peeling. What’s the real cause?
Neglect!
What’s even more amazing is that the majority of people don’t even know what they’re supposed to be doing
to take care of their wood - like cleaning & sealing it once in a while. Many deck owners believe that the wood
used on their deck does not need added protection, only to find out too late that this is a costly assumption.
Here comes the Professional Wood Restoration Contractor, riding in on his white horse. He or she can
rescue a customer’s gray, weathered deck and bring it back to life. If that doesn’t make your heart thump,
how about all of the other markets open to you? Wood fences, wood-sided homes, log cabins, cedar shakes
and other wood surfaces certainly can be fun and lucrative. There are also plenty of add-ons including
outdoor furniture, playground equipment and more.
Beyond new construction, wood is being replaced all across our country at an alarming rate. This is wood that
might have been saved if it was properly maintained. The cost of some wood is increasing at an alarming
rate, too. Today the replacement cost of a wood deck or fence can be out of reach for some homeowners.
Our country is actually running out of trees to build new decks and fences. Very soon, the wood restoration
business will be the only hope we’ll have to be able to enjoy a beautiful deck, fence or wood-sided house.
Wood restoration and maintenance is fast, easy, and profitable. Homeowners love the results and love you
for restoring the natural beauty of their wood.
What about the advent of wood substitutes? Composite decking has entered the market in a big way. Is the
future of this business in jeopardy? These types of decking will still need to be washed to rid them of mold,
mildew, and algae. Many of these products have serious downsides as well. Some brands give a “10-year
warranty” which should send off bells and whistles to many end users since wood that is properly cared for
will last more than 20 years! Some of the products are limited in color, get too hot, leach tannin stains, attract
mold and mildew, and the list goes on. The one rule of thumb to always keep in mind is that if it has any wood
content at all, it requires a preservative.
“Do-it-yourselfers” and “hack” contractors will continue to scar the industry and cause an increased need for a
professional wood restorer. The opportunities in this industry are endless. Another great feature of this
industry is that there are many other related professions that tie into wood restoration (painting, pressure
© 1999 - 2010, Contractors Foundation
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washing, building maintenance, deck building, siding, window cleaning, etc.). These will be discussed during
the class time and in this manual. Wood Restoration can be treated as a sole business and profession or
possibly as an add-on to another business.
These next several days are going to teach you how to bring that tired, old, gray, rotting deck back to life.
We will also teach you how to keep that same deck looking great year after year, while bringing in repeat
business for a more secure future.
The business of wood restoration is not only easy, lucrative, and fun; it’s environmentally friendly and…
…It saves the trees!!!
© 1999 - 2010, Contractors Foundation
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THE WEATHERING PROCESS ON WOOD
(The scientific explanation)
The natural weathering process of
wood is actually a very complex
combination of chemical, mechanical,
biological, and light-induced processes,
which interact and change the
appearance
and
integrity
of
unprotected wood exposed to the
elements.
These processes are caused by the
decomposition of wood components by
moisture, sunlight (ultraviolet radiation),
temperature, oxygen, atmospheric
pollution and airborne fungal spores.
These factors combine to physically
and chemically attack wood lignin, the
chemical structure that holds wood
together. Once wood surfaces turn
gray, the surface continues to slowly
erode.
(And now for the real-world explanation)
The forces of weathering can be devastating to wood. Moisture from rain, snow, and dew are quickly
absorbed by unprotected wood causing it to swell while washing out the natural wood resins and coloring.
The heat from the sun dries and shrinks the wood. These daily cycles of wet and dry swelling and
shrinking causes the wood to warp, splinter, cup, crack and become discolored while allowing the sunlight
(UV) rays to break down the cell structure and degrade the integrity of the wood.
Moisture that is allowed to sit in the wood will
soon serve as a natural food source for mold,
mildew, algae, and fungus causing black,
green or gray discoloration.
Since decks are horizontal surfaces, they hold
water, snow and dew for longer periods of
time - which accelerates damage. Deck floors
get 40 to 50 percent more UV radiation from
sunlight than comparable vertical surfaces.
The prolonged dampness attracts dirt from
atmospheric pollution and airborne fungal
spores. Although nature is actually what
damages wood, it is homeowner neglect that
causes the damage – or allows it to happen.
The temperature difference between the sun-exposed top of the board and the shaded bottom can be as
much as 50º F. In addition to this, decks are subject to more foot traffic than other structures.
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What are the signs of degraded wood? Aside from the classic grayed-out look, deck boards show their
degraded condition a number of ways. For example, weak or spongy boards have lost their strength through
the weathering cycle. Once a board has begun to flex or bend, it is only a short way from collapsing under
normal weight. Another example is “checking” (where the surface of the wood shows cracks that run against
the grain. This is obvious water damage, and the board should, most likely, be replaced. Splits in the wood
along the grain are signs of excessive drying (caused by the leaching out of the natural moisture and oils).
Cracks like this do not weaken the wood but they do take away from the appearance of the wood. This
cracking can be prevented to some degree by sealing the wood early in its life. Nothing, however, can be
done to repair any damage to wood once it has occurred. Damage can be slowed or stopped with careful
maintenance, but never reversed.
Typical photo-degradation on siding.
Notice that the area protected from sun by the overhang is not really affected.
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Factors that affect the appearance and life of wood exposed to the weather
Wood weathers and decomposes due to many elements in nature. It is the interaction of these elements
that causes wood to decay and lose its strength and natural appearance. The two major elements include
moisture (rain, dew) and sun (ultraviolet). The damage caused by sunlight is the first visible damage,
while the damage caused by moisture is the most significant over time. Other factors include temperature,
mold, mildew, excessive traffic, location of deck (near pool, to close to the ground), and other
miscellaneous factors. All of these factors accelerate the weathering process by breaking down the lignin.
Lignin is the glue-like substance that holds wood together. When this occurs the results include excessive
splitting, checking, raised grain, extractive bleed, and discoloration.
Location
Location and use of the deck may also add to or subtract from the life of the wood. If this is a planned
project consider items such as uses, elevation, and location on property. If a deck is built too close to the
ground it may cause the wood to be a haven for mold and mildew as well as result in a higher moisture
content in the wood. Wood that is in shade will wear differently than wood exposed to more constant
sunlight and UV rays. It is important to keep wood away from contact with the ground surfaces that will
soak in moisture. It is very important to suggest a high-quality sealer based on the location and use of the
deck.
Moisture - Expansion and Contraction
Wood is constantly shrinking and swelling as it gains and loses moisture. This moisture can be due to
humidity, rain, or the presence of water (leaky gutters, etc.). When humidity is high wood cells will “sweat”
which can cause moisture and adhesion problems. Such moisture changes cause the wood to become
compromised and are a huge factor in exterior wood restoration.
Mildew
Mildew is a common term used in the industry as it affects both the sealer’s appearance and
performance. It is very important to rid surfaces of mildew. Mildew is a stain fungus that does not degrade
the structure or strength of the wood. Mildew can cause an unsightly appearance on the sealer. Natural
oil stains and sealers can be a food source for mildew because they contain natural sugars and starches.
Like any foreign matter on the surface of the wood, mildew can cause adhesion problems for the sealer if
not removed.
Ultraviolet Radiation (UV)
No matter the care taken to extend the life of wood, it ages and degrades from the sun’s ultraviolet rays. If
wood is left unprotected degradation can occur within weeks. It is recommended to rewash or rejuvenate
any wood left exposed for more than 30 days. Ultraviolet rays will have different effects on different types
of wood. Some wood will lighten from UV rays and some will darken. The main characteristic is a grayedout look on the wood surface.
© 1999 - 2010, Contractors Foundation
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WHAT KINDS OF WOOD ARE USED ON DECKS?
There are three types of wood commonly used to build decks – pressure-treated pine, cedar, and redwood.
Other types of wood are showing up in different regions of the country and are included here for discussion
purposes.
Pressure-Treated Pine:
The most popular choice of materials in the US, primarily because of
cost and durability, is pressure-treated lumber. About 80% of pressure
treated wood is Southern yellow pine. It has a very pronounced grain,
with a yellow-green hue caused by the CCA chemical treatment of the
wood. It is graded Select, #2 and better, and construction grade. In the
eastern half of the US, more than 80% of all decks are built from this
wood. Usually this is southern yellow pine that has been injected with
a chemical called CCA (chromate copper arsenate). Pressure-treated
pine has good structural strength. It is cheaper than redwood and
cedar and has good protection from fungus, mold, mildew, and
insects. To identify pressure-treated wood, look for a wide grain pattern and a greenish hue. Pressuretreated lumber is reasonably hard, and doesn’t dent very much with your thumbnail.
The injection process involves forcing the chemical into the wood at high pressure, driving it into every
cell of the wood. Until recently, this chemical was Chromate Copper Arsenate (CCA), a known poison and
carcinogen. CCA dissolves in water and rain causes it to leach out and contaminate the soil. As leaching
occurs, the wood fibers shrink and the pine shrinks, checks, and cracks.
Treated pine must be sealed to stop the leaching, shrinking, and cracking. Once-beautiful treated pine
decks can become a nightmare of cracks and splinters if not protected by a penetrating permeable oilbased wood stain/sealer. Be aware that the EPA and the wood industry have agreed to stop making CCA
lumber. There are alternative pressure-treating chemicals that are more expensive but arguably safer to
be around. New pressure-treated wood is predominantly ACQ, which is a much safer alternative to
CCA. Wood treated with ACQ is safe enough not to require a warning label, unlike CCA. With the main
ingredients being 100% recycled copper, together with a natural base of Alkaline and Quat (a fungicide)
ACQ is safe to handle, even without gloves. The EPA has stated that sealing any existing CCA lumber
regularly is the best way for homeowners to minimize the danger to them and their family. More
information is available at the EPA website, currently found at www.epa.gov/pesticides/citizens/1file.htm
Redwood:
Appearing predominantly on the west coast, redwood is available in
several grades, which vary considerably in appearance and quality. The
color will vary from a light red to a dark reddish-brown. It's graded in
Clear Heart, B-Grade, Construction Heart, or Construction Common.
The Clear Heart grade is more durable than the other redwood grades
because of its high resistance to decay.
This is the grade that redwood rests its reputation on. Redwood is a soft
wood and weathers to a yellowish-red very quickly. Redwood has
natural protection in the fiber of the wood. The tannin or tannic acid
found in redwood is good protection from rot, mold, mildew, and insects,
but the tannin will leach out with repeated exposure to rain and the wood will soon decay. The heart of the
redwood has the highest concentration of tannin but the heart redwood is only found in mature trees.
Mature redwood trees are hard to find now, because we have harvested almost all available virgin
forests. Most of the redwood that goes into wood construction today is from the sapwood (outer part) of
the younger second growth trees, which is less resistant to decay. Redwood must be sealed to protect it
from the effects of rain and UV rays. A preservative finish can be used to provide extra protection against
rot and decay.
Redwood used for decks tends to be fairly firm with few or no knots.
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Cedar:
Usually Western Red Cedar. Newly cut cedar has a color range
from light browns and tans to almost a salmon pink. It usually has a
tight, fine grain. Left untreated it will eventually turn silvery gray and
then to a very dark brown. It's graded A, B, C, or D. This soft wood
is more durable than most woods in common use. It is resistant to
decay, but relatively soft and quick to weather. Preservative
treatment/sealing is recommended. Cedar may have many knots.
Dimensionally stable, it doesn’t warp. Cedar will wear excessively in
front of doors and when used as stair treads. When cedar fails, it
usually appears as rot on the very ends of the boards. Tannin is
found in cedar as a natural protection from insects, fungus, mold, and mildew. Cedar is less expensive
than redwood, but does not have the structural strength of redwood. Like all other types of wood, it must
be sealed with permeable wood sealer to protect it from water and the ultraviolet rays of the sun. Just like
redwood, a preservative finish can be used to provide extra protection against rot and decay.
Cedar used for decks tends to have a lot of smaller knots. Cedar is so soft that your thumbnail will
produce a deep gouge in the surface, so it is fairly easy to identify.
Mahogany:
Mahogany is showing up in areas like the northeast as a deck-building
lumber. Mahogany is considered by many to be the finest outdoor wood
in terms of appearance and durability. Mahogany has an interlocking
grain that prevents separation between annual growth rings, making it
one of the most stable woods available. Mahogany is an extremely
dense lumber. It comes in clear grade only, no knots or sapwood. Not
all mahogany has the natural resistance to decay needed for outdoor
use. The mediums to dark red and brown species are more resistant to
decay. Colors range from a light tan to a deep rich brown.
Second only to Ipe in strength and durability, this rich elegant lumber
can be breathtaking when properly maintained. Mahogany does not
contain tannins, so the wood does not stain when it comes into contact with metal. Cost of construction is
more than a clear cedar deck but usually less than one made from Ipe. If left unsealed, the wood will
weather to a silver patina.
Mahogany is a very firm wood, and your thumbnail will not dent this wood significantly.
Ipé:
(Pronounced ee-pay)
This wood is also called Pau Lope or
ironwood. It is so named because of its incredible hardness or
density. Also nicknamed Brazilian Walnut, this species comes from
Central and South America. Many times harder than oak and
extremely resistant to rot, decay and insects, and even fire, no other
material will outlast Ipé. It is dark olive brown in color with an oily
appearance and no knots. Even with no sealer this wood will remain
smooth and splinter free for a long time. These woods, however, will
turn silver gray very fast if not sealed or stained with an ultraviolet
(UV) protector. This material comes from second and third world
countries. We have no conclusive evidence as to whether or not this
product is endangered. These woods only grow in areas of the world
that are known to have deforestation problems.
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Ipé is very difficult to cut, route and fasten because of its incredible hardness. This makes Ipé the most
labor-intensive material to use for deck construction. Each board must first be end sealed after each cut.
Each screw hole must be counter drilled and pilot drilled before each screw is applied. Even the shear
weight of the material comes into factor.
There are a number of other exotic woods that are finding their way into the marketplace, including
Siberian Larch, Cambara, and others. These woods tend to be hardwoods that are dimensionally stable
and can often be treated exactly like Ipé
Old-growth redwood stand
© 1999 - 2010, Contractors Foundation
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EQUIPMENT NEEDS
Power Washer – Keep in mind that cleaning wood with a pressure washer is more a function of rinsing
than scrubbing. That means that the GPM rating of your machine is more important to you than the PSI
rating. You should look for a minimum of 700 PSI & 3 GPM for use on wood. This is all the pressure than
you will need 99% of the time, but there are some occasions when more pressure might come in handy.
We recommend a larger machine for general use, such as 3000 PSI & 4-5 gallons per minute. This size
of machine will wash anything including concrete. The lower the GPM (gallon per minute, or volume) the
more time you will spend washing and rinsing, and the less you will make per hour with your machine.
Look for a name brand, rebuild-able pump such as General, AR, or Cat. Look for a reputable motor, such
as Honda. Kohler and Vanguard are also excellent. Hot water damages wood, so if you intend to do
decks and fences, a cold-water portable is a wise choice and probably all you need. If you need hot water
for other jobs, you can use the same equipment on wood without turning the burner on.
If you are buying a larger, generalpurpose machine, look for belt-drive.
Smaller, direct-drive machines are
very affordable and much lighter, but
the pumps on direct-drive machines
wear out in half the time that pumps
last on belt-drive machines.
Carry at least 100’ of high-pressure hose. A second length of hose
comes in handy. Always use quick-connects, keeping the male and
female ends coordinated. Most contractors start with the female end
at the machine and work their way out to the wand. Many even use
quick- connects at the end of the wand to make changing tips easier. There are different styles of quickconnects and they don’t interchange – so be consistent. Add a high-pressure swivel between the trigger
gun and the hose to prevent fighting the hose and make your entire day go better.
Carry at least two 50’ garden hoses (in 5/8” diameter, to deliver all of the water possible to your machine).
Always keep a few spare hose washers and O-rings available. Consider a shut-off valve for the hose that
you can install at the machine. Inexpensive in either plastic or metal, these valves will save you a lot of
steps each day.
Sprayers. Powered sprayers are much easier and more consistent than pump-up sprayers. Look for a
quality wand and tip with any powered sprayer. Keep spare tips and wands available to handle field
emergencies. For oil sealers, airless sprayers atomize too much to be effective. For latex or acrylic
sealers, airless sprayers can be effective.
Ladders. Always look at the weight rating of a ladder before purchasing. Lightweight ladders are easier to
move around but are far less stable to use. You might consider fiberglass construction with metal rungs,
but they tend to be quite heavy. Always look for safety tread rungs. Look for cleated feet for extension
ladders. A good assortment of ladders includes an 8’ stepladder and a 24’ extension ladder. Sometimes
you will even need a longer (32’) extension ladder. Consider buying ladder levelers if you work on rolling
terrain. Note: Never extend an extension ladder all the way, and always tie off the top of an extension
ladder for safety.
Extension Cords. Select heavy cords (minimum 16 ga. and preferably 14 ga.) to minimize voltage drop.
Maintain the integrity of the grounding system. Maintain or repair cuts to the outer skin of cord.
Tarps. You can never have too many of these on the job. An assortment of tarps is ideal. Absorbent
tarps, such as paper or canvas make great barriers for sealers. Sheet plastic can be used to protect
vertical surfaces, or underneath absorbent tarps. Remember not to use plastic sheeting over plants and
vegetation.
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Brushes. Chinese bristle brushes are the ONLY recommended brushes to use for sealers. They hold a
lot of product and don’t leave brush marks. They are more expensive but worth every penny. It is also
important to keep on hand “cheap” brushes or retired, old staining brushes to use when “cutting in” or
applying chemicals. So don’t throw away the old brushes as they may have other uses. “Cutting in”
means applying chemicals or sealers to hard-to-get-to places where a sprayer or other application
method may be difficult... In other words, you would not want to use a sprayer to apply a sealer
immediately next to a house or structure. In this case you “cut in” so many boards or spindles with a brush
before the use of the sprayer.
Wands. The wands used with a washer can be very important. Having different length wands can make
easy work out of hard to reach places. A short wand is excellent for washing the outside of deck railings
from the inside of an upper level deck. A long wand helps in reducing splashing in difficult areas like the
underside of an upper level deck. A dual lance wand can apply chemicals at low pressure and rinse at the
same or slightly higher pressure without changing wands or tips. A dual lance wand applies to wood
restoration in that you can use this type of wand to regulate pressure as needed on wood surfaces where
needed.
Tips. There are two factors to consider when selecting the proper tip: the orifice size and the spray angle.
The orifice size determines the quantity of water and the pressure you will use. The spray angle
determines the pattern of the spray.
Tip sizes are shown two ways. The first is a 4 or 5 digit number. In this method, the first two numbers
indicate the angle of spray and the next 2 or 3 numbers indicate the orifice size. A 2505 is a 25º tip with a
#5 (or #05) orifice. The other way that tip sizes are identified is by color-coding and by orifice size.





Red (0°) - The most powerful, not recommended
Yellow (15°) - Used mostly on masonry, not recommended
Green (25°) - The most commonly used, and is excellent on most surfaces including houses
White (40°) - Best used on wood surfaces
Black (Chemical Tip) - Mostly used on low pressure to apply chemicals
These color-coded tips can be bought in various orifice sizes (such as #5, etc.).
To determine the orifice size, use the chart found on the next page. In that chart, you will find that if you
have a 3000 PSI pressure washer that puts out 4 gallons per minute, you should use a 4.5 tip size.
Stepping up to a larger size reduces the pressure (and increases the GPM). Stepping down a size
increases the pressure (and reduces the GPM). Never drop below the nozzle size recommended for your
machine. This can be dangerous and can damage the machine.
This can all seem like higher math, but the chart makes it simple. Cut out a copy of the chart and pin it to
a wall in your shop area. With a highlighter, mark the column under the pressure output of your machine.
Now highlight the row with the GPM output of your machine. You will see the orifice size that you should
use. A 3000 PSI machine that puts out 4 GPM should use a 4.5 orifice tip size. If you wanted a 25º tip for
this 3000 PSI machine, you would buy a 25045 or a Green 4.5.
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Inexperienced operators sometimes decide to reduce the pressure output of their machine by backing the
Unloader off. The Unloader is a safety device and should not be field-adjusted. Backing off the Unloader
reduces both the GPM and PSI output of your machine, making you less efficient.
We teach three ways to reduce pressure without harming your machine – increasing
the tip size, holding the tip farther from the surface you are cleaning, or using a duallance wand. Of these, using the dual-lance wand or increasing the distance between
the surface and the nozzle gives you the most flexibility without the need for tools or
‘time outs’.
Selecting the angle is a simpler task. Each contractor has a preference. 40º tips
cover a wider path with each stroke and are preferred by many. 15º or 25º tips
concentrate power into a smaller path, and are considered by some to speed up a
stripping job. We NEVER use a 0º tip on wood. If you are using a dual-lance wand,
the second tip on your wand should be your Chemical Injector, or Dump, tip (the
Black one).
NOTE: Never use a rotary tip on any soft surface like wood. These tips can etch concrete in less than a
minute and are capable of digging into cedar ¼” deep within a few seconds.
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EQUIPMENT MAINTENANCE
There is nothing more frustrating than driving to the job site, removing the furniture from the deck, and
setting up all the equipment - just to find out that some tool doesn’t work. In the wood restoration business
your tools are your bread and butter.
Fortunately, our trade doesn’t require too many serviceable tools, but it only takes one breakdown to ruin
your whole day and throw your entire week’s schedule off.
Following is a list of the most common tools we use, and the attention they require.

Airless sprayers: High maintenance sprayer. Depending on what type material
you have run through it, rinse after every use with hot water, thinner, or diluted
sodium hydroxide solution (10 to 1). Be sure to follow all manufacturers’
recommendations for proper, safe operation. Store indoors & do not allow any
liquid inside the tool to freeze.

Powered Sprayer: Depending on what type material you have sprayed, rinse the
system out at the end of the day with a diluted non-caustic solution (such as a degreaser). Then rinse
again with clear water. Leave clear water in the lines to prevent accidents. Be sure to follow all
manufacturers’ recommendations for proper, safe operation. Store indoors & do not allow any liquid
inside the tool to freeze.

Pressure washers: Really no need to rinse this machine out. The single most important point to
remember is to never allow your machine to run without water flowing through it – even for a few
seconds when you are starting it. Damage to the pump occurs within seconds if it runs dry. Never run
the engine without pulling the trigger every minute or so. The small amount of water trapped inside
the pump when the trigger is not pulled will reach boiling point in a short time, and pulling the trigger
allows cool water to enter the pump – and prevents damage.
The next most important thing to remember is to check
the oil level daily in the engine as well as the pump.
Dipsticks are provided for both. The engine and pump
demand two different types of oil. Change the engine oil
every 3 months. Do not overfill! The better machines
available today are driven by engines with oil-cutoff
switches. Never disable this function, because it will
save your engine from being destroyed by poor
maintenance practices. Low oil or even dirty oil will
cause the motor to start missing, and eventually it will
stall and be unable to start. Many manufacturers
recommend that you change the pump oil every 200
hours, which is about every month or two for most contractors. Using the dipstick or sightglass, be
sure not to overfill the pump either.
Never change the factory setting on the unloader, as this will affect your machine’s output and could
affect the warranty. Check the tightness and condition of the belt at least once each season. If you
use the downstream injection system, realize that the chemicals you use may adversely affect the
hoses, quick-connects, and your trigger gun. Be sure to rinse out your system after using your
injector. Be sure to follow all manufacturers’ recommendations for proper, safe operation. Store
indoors & do not allow any liquid inside the tool to freeze.
© 1999 - 2010, Contractors Foundation
14
EQUIPMENT HINTS

Every morning, before you leave for the first job, plug in and/or turn “ON” any powered tools to
double-check that they are operational. It is much easier to fix something in your garage than in
the customer’s yard.

Dragging black high-pressure hoses across concrete will cause wear spots, causing them to burst
prematurely under pressure. This can be extremely dangerous. Handle hoses carefully, and
inspect them regularly. Dragging these hoses can also leave some pretty ugly black marks on the
customer’s driveway!

The “O” rings used in quick-connects fail regularly. Always keep a number of spares available for
installation on the job. While you are at it, keep a spare hose washer handy, too. There are two
materials typically used for “O” rings – BUNA and VITON. VITON is more chemical- and heatresistant, but often costs 3-5 times as much. BUNA is completely satisfactory for cold-water use.

Wipe off your equipment regularly. It will be nicer to handle and will create a more professional
appearance.

Never leave rags resting on running equipment. Your equipment is air-cooled, and rags interfere
with that cooling. Rags can easily become caught up in spinning belts and pulleys. Rags can
catch fire from hot engine parts or exhaust gas.

You are likely to be filling gasoline cans daily. There have been many reports of explosions
caused by static electricity when someone has tried to fill a gas can that was sitting on the bed of
a van or pickup. Always set the gas can on the ground when refilling it.

Always set your pressure-washer on level ground. This keeps the oil flowing in the engine. If your
machine vibrates excessively, causing it to move around on its own, anchor the wheels with
chocks.
© 1999 - 2010, Contractors Foundation
15
OTHER MISCELLANEOUS EQUIPMENT - CLEANING
1)
Garden hose (100ft) w/shut-off valve (optional) & spray nozzle
2)
Leaf blower or broom
3)
Moisture meter
4)
Spinning surface cleaner
5)
Pump-up sprayer for back-up
6)
Gas can
7)
Plastic buckets (2-3)
8)
Stripping paint brush (nylon or polyester bristle) for cutting around house
9)
Safety gear, goggles, respirator, gloves, face shield, hat, etc.
10)
Basic tool kit; hammer, drill, drill bits, screws, pliers, hose
clamps, etc.
11)
Yard sign, your company name and phone number
12)
Ramps for loading & unloading pressure washer, (optional)
2x6x8’s work well
13)
Rags or Paper Rags
14)
Glass cleaner
15)
Camera (digital preferred, 35mm is OK)
16)
First Aid Kit with Eyewash cup and solution
Dual lance wand. Note the valve on the side.
© 1999 - 2010, Contractors Foundation
16
WOOD CLEANING & BRIGHTENING CHEMICALS
Years ago, the art of cleaning wood was simply to power wash it with as much water pressure as one
could muster. Unfortunately, this practice is still going on today by those who don’t keep themselves on
top of current technology. These days smart contractors allow chemicals to do the work for them.
The first thing that must be stated is that pressure can cause damage. The use of the proper chemicals
and restorative agents are key to ANY wood restoration. There is a line between being a wood restoration
professional and a vandal. This may seem like a hard line to take but as more people enter this industry
without the proper knowledge and education the more damage that seems to be caused. IF you are
restoring wood without any chemicals at all you are not a professional and in all likelihood a vandal. By
using pressure only you are “water blasting” the wood surfaces, really not much different than sand
blasting, or other high-pressure methods. For wood it is not the pressure that cleans and restores wood, it
is the chemicals. Water and pressure alone will not remove mold and mildew, will not brighten wood, and
will cause the need for excess water pressure to reach the raw wood. The proper method is to let the
chemicals work on the surfaces based on dwell time so that finishes will melt off and require much less
water pressure to remove. A pressure washer is like a saw or hammer to a carpenter, it is merely a tool to
make the job easier. A pressure washer should be viewed as a large rinsing machine that saves time and
labor. Think of an oven cleaner in your home. If you scrubbed your oven without an oven cleaner it might
take you many hours of scrubbing to get clean. The use of an oven cleaner allows the debris and grime to
lift off of the surfaces and make it much easier to clean with better results. Wood restoration is just this,
chemicals are used to make it easier to clean and restore with much better results. It is also important
when cleaning the wood that all surfaces must be clean and free of any inhibitors that may cause sealer
failure. To understand what chemicals should be used to prepare the surface requires a solid knowledge
of chemicals and the realization that there are many different circumstances and conditions of wood
projects you will encounter. It is best to view jobs like a fingerprint and that no two are the exact same.
Attempting to perform every job the same way or trying to plug in a formula that is the same on every
project will not work for the true professional. Some require sanding, some repairs, some cleaning and
brightening, some stripping, and many other combinations and methods to achieve maximum results.
Mentioned above is dwell time. Dwell time is the time you allow a chemical to remain on the surfaces to
actually work. It is important to follow manufacturer recommendations on dwell time. If a stripper has a 30minute dwell time then you should allow the full 30 minutes and not remove in 10 minutes because it
seems to be working. A simple test for anyone to see first hand the results of dwell times is to apply a
stripper to the surfaces and wash a section at 10 minutes, another at 20 minutes and finally again at 30
minutes. Brighten all areas together and watch the results as the wood dries. There are many factors that
may effect dwell times. These will include chemicals remaining wet to be active, temperatures that cause
ineffectiveness or extended dwell times, multiple sealers of product, stains vs. sealers, and more.
Chemicals are the most important tools to your arsenal of wood care because the preparation and work
put into the project prior to sealer is the most important. If the wood is not properly prepared before sealer
you may have adhesion problems and shorter life of the product. More importantly, any imperfections in
the wood appearance are usually magnified after a sealer has been applied. The more effort you put into
preparation the better the end result of the project.
Chlorine bleach (sodium hypochlorite): One of the most widely used cleaning chemicals today is
household chlorine bleach. Many manufacturers have maligned the use of bleach over the last several
years. Bleach alone will remove mold & mildew stains but won’t deep clean the wood. Bleach may affect
Dursban, the predominate termite treatment today.
The US Department of Agriculture (Forest Products Laboratory Chemist, Dr. Mark Kanaebe, Madison,
WI.) says that a mild sodium hypochlorite solution mixed with water and a small amount of a woodfriendly detergent is one of the best solutions for cleaning decks. Scrubbing and rinsing with light pressure
is also needed since he does not recommend high-pressure removal of gray dead fibers from the wood.
Most professionals discourage the use of bleach because of the potential for damage to the wood
and surroundings.
© 1999 - 2010, Contractors Foundation
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At this time the Forest Products Lab is reconsidering its previous recommendation about using bleach on
wood. Bleach will destroy lignin, and any use of it on wood has to be extremely careful.
Bleach opens the pores of the wood.
Bleach is an alkaline, so it must be neutralized with Wood Brightener.
Never use bleach stronger than 1% - 2% because it will “burn” the wood.
SAFETY NOTE: NEVER mix bleach with any product containing ammonia. The combination of
bleach and ammonia produces a deadly gas. Never mix bleach with percarbonates because the
chemical reaction produces excessive gas that can cause a container to explode.
Oxygenated Bleach, Percarbs (aka Sodium Percarbonate) A mild, environmentally friendly oxidizer. This
powder must be dissolved in warm water prior to usage. Once mixed, this product becomes activated and
must be used within 6 hours. Requires a higher degree of power-washing pressure (1000 PSI). Neutralizing
is not needed, but always recommended. Safe for plants, grass, and animals. Ideal for newer wood that has
not been previously sealed, and particularly useful for maintaining decks that were previously sealed with a
fully-penetrating oil.
Caustic stripper/cleaners (containing Sodium Hydroxide) Very popular with professionals. Caustics will
strip off multiple coats of oil-based paint or sealer. The stripping process can be done at low pressure (300
PSI to 800 PSI). Sometimes multiple strips are necessary to get rid of all or most existing sealer. All sodium
hydroxide strippers stop working if they dry out on the surface. A “splash test” will reveal the presence of any
remaining sealer. Extreme caution must be used when applying sodium hydroxide chemicals around plants
and animal life. These cleaners have a high alkaline pH and can cause burning to the skin and eyes. (Safety
goggles and rubber gloves are recommended for your personal protection.) Considered environmentally safe
to use.
NOTE: The use of alkaline chemicals such as bleach or sodium hydroxide will
result in two major concerns for the wood restoration professional.

Fuzzies: Strong alkaline chemicals melt the lignin in the wood, causing
fibers to stand free. These free-standing fibers make the wood look fuzzy.
See the picture of a fence with fuzzies. (Lignin is the natural component
(glue) which holds the wood fibers together.)

Dark Wood: Cedar & redwood will turn black from extractives (after being
treated with an alkaline, the wood must be neutralized with Wood Brightener this step will make the wood return to its natural color).
Tri-sodium Phosphate: (TSP) TSP has been a long time standard for many basic cleaning jobs from house
siding to convertible tops. The cleaning power comes from the high degree of alkaline in this chemical. Used
primarily by poultry producers to reduce salmonella contamination in chickens. 1 cup per gallon makes a
basic household cleaner. Not recommended for wood. The phosphate in TSP is considered an environmental
problem.
Phosphoric acid: A slightly acidic additive developed primarily to put the fizz in soft drinks. Because of its
acidity it has been used to neutralize (lower) the pH of wood after the use of strong caustic strippers.
Phosphoric acid will remove tannin (tannic acid) and rust stains from wood.
Citric acid: Derived from citrus fruits, citric acid was formed as an additive to soft drinks and cheese for
flavoring. Because of its gentle acidic nature, it too can be used as a neutralizer. Not as harsh as oxalic acid,
it is used on such hardwoods as oak, mahogany and walnut as a neutralizer.
Oxalic acid: The most common of wood brighteners and neutralizers used in the wood restoration industry
today. Commonly known as “wood bleach”, oxalic acid occurs as the free acid in beet leaves and rhubarb. It
© 1999 - 2010, Contractors Foundation
18
is also obtained as a byproduct in the manufacture of citric acid. Widely used in the leather bookbinding
industry to clean leather before tooling. Oxalic acid is best for removing tannin (tannic acid) and leaf stains
from wood.
Wood Brighteners: These are proprietary blends of acids designed to neutralize and to remove unsightly
stains, giving the benefits of each different acid. Low cost and easy application. Comes in liquid or
powder and has a 30 day shelf life after mixing with water.
NOTE: The proper use of chemicals is an essential element of your professionalism. Become as familiar as
possible with your preferred products by using them exclusively. Brand-hopping will lead to inconsistent
results and unhappy customers.
NOTE: Avoid the temptation to use raw chemicals. Untrained use of raw chemicals is extremely dangerous
and can result in serious injury or death. Commercially-prepared products are designed for the job and for the
operator. Commercially-prepared products come with warranties and liability insurance coverage for your
protection and your customer’s safety. If you use raw chemicals, YOU are liable for any resulting problems.
© 1999 - 2010, Contractors Foundation
19
pH SCALE
To understand why chemicals work the way they do, you will need a fundamental understanding of the
pH scale. This is the universal tool for describing chemical properties.
pH (Potential of Hydrogen)
A measure of the degree of the acidity or the alkalinity of a solution as measured on a scale (pH scale) of
0 to 14. The midpoint of 7.0 on the pH scale represents neutrality, i.e., a "neutral" solution is neither acid
nor alkaline. Numbers below 7.0 indicate acidity; numbers greater than 7.0 indicate alkalinity. It is
important to understand that pH is a measure of intensity, and not capacity; i.e., pH indicates the intensity
of alkalinity in the same way temperature tells how hot something is - but not how much heat the
substance carries.
The pH scale is logarithmic which means that moving on (unit either way on the pH scale results in a 10fold increase in the degree of alkalinity or acidity.
Some typical pH values are included in the following table:
pH
Product
0-1
hydrochloric, sulfuric,
nitric acids
phosphoric, sulfamic
acids
citrus fruit
milk
1-2
ACIDIC
2.0
6.5
NEUTRAL
7.0
ALKALINE
8.0
11.0
13-14
eggs
ammonia
caustic soda,
strippers
floor
As a general rule of thumb, cleaning performance on typical oily soils is enhanced with an increase in
pH. Some soils, for example hard water deposits, are best removed with acids.
© 1999 - 2010, Contractors Foundation
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CHEMICAL COSTS
The contractor sometimes thinks of cleaning products and strippers as “expensive”. The right way to think
about chemical costs is that they save you time and, therefore, save both you and your customers
money. Always remember: it is the customer who pays for the chemicals you use - not you! Your
customers deserve the best you can find – and at the best cost possible.
The smartest way to think about the cleaners you use every day is this: If $5 worth of product saves you
15 minutes of time, they are a bargain. If you, like most of us, are targeting a goal of $100 per hour in
business, then saving 15 minutes is like saving $25 worth of time. Slam dunk!
Contractor-grade name-brand wood strippers can cost anywhere from $10/gallon to $65/gallon. There are
specific instances when spending this amount of money is absolutely necessary (and can lower the final
cost of labor on the job). In 95% of the cases, however, generically-priced products are stronger and will
do the job better and faster at a fraction of the cost than national brands bought in ‘big box’ stores.
Here’s food for thought: In a world where McDonalds gets sued because the coffee is hot, who do you
think gives the final approval to the products sold by the ‘big box’ stores? That’s right! The lawyers do!
Since most of these stores cater to do-it-yourself home owners, the products they sell are diluted to be
less dangerous. You will be better-served by seeking out stronger products sold by suppliers who cater to
contractors instead of home owners.
© 1999 - 2010, Contractors Foundation
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THE DECK CLEANING PROCESS
1. Call ahead, at least one day before, to confirm the appointment. You should ask the customer if
they have any questions. Also, confirm at this time that water and electricity are on and operating.
If they are not you could lose a days work.
2. Be sure that all of your tools and a full assortment of cleaning products are properly placed in
your work vehicle each morning before leaving for any washing job.
3. Make sure everything is working properly before you head out.
4. Be sure to take customer’s work order with you.
5. Plan to arrive no earlier than 8:00 AM.
6. Upon arrival, notify customer of your presence. Always knock at the front door to introduce
yourself and take a “before” picture. A true, professional company will make sure that the person
introducing himself is in a company uniform. This also gives the homeowner a more secure
feeling of just who is knocking on their door. If a two-person crew, one knocks on the door to
notify occupants and the other starts unloading and carrying tools and material to the work area.
7. Next, take a picture and mark exact location with a flag or a golf tee. Note the time of day of your
photo on your copy of the invoice
8. Remove all furniture, plants etc. from deck; set in a safe place (not under the deck.) An area off
the grass and away from the deck is best. Leave barbecue and heavy items in place. Move any
items from underneath the deck.
9. Blow off leaves and debris.
10. Make any necessary repairs at this time. Boards blend in better for the end result if they are
replaced before the cleaning process begins. Wood that is replaced new after cleaning will show
a greater contrast than if replaced prior to being cleaned as the chemicals and cleaning process
help in reducing this contrast. Sometimes the homeowner may have extra boards from when the
project was new that will help in reducing the contrast. It is also important when using new boards
to set the expectation first that a new board will not initially match the older boards. In time this
the contrast will reduce and it will eventually be difficult to tell the old boards from the new boards.
If using a hammer on “popped nails” it is recommended to use a punch, so as not to leave marks
around the nail heads.
11. Pre-wet and cover all plants before spraying cleaner/stripper. By pre-wetting you help ensure that
any chemical will be further diluted if it reaches that surface. Also, the surface must be wet for the
chemicals to be properly effective. If you are working on an elevated area be sure to mask off
lower areas. If you are working over a patio it is recommended to pre-wet substrate and then use
a combination of a canvas (absorbing) and a tarp on plastic to cover and protect surfaces. If you
use paper drop cloths with a poly liner over plants, use the plastic side up when you apply
cleaners and remove the tarps before you begin to wash.
12. You might want to cover any electrical outlets or telephone jacks with tape, in case you might
spray these outlets with water during the wash process - water & electricity don’t mix.
13. Cool the deck down if necessary by misting water on it or by placing a tarp over the deck for 20
minutes or so. On hot days you may have to cool the deck down often.
© 1999 - 2010, Contractors Foundation
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14. Mix deck-cleaning solution.
15. Apply your cleaner of choice, careful to avoid getting
chemicals on the house paint or aluminum doors or trim. Be very
careful not to apply chemical to other surfaces that may be
damaged. As necessary, use a brush and “cut in” to those areas.
For example, along the siding of a house you would not want to
spray chemicals within a few feet from that siding or other
substrate.
16. When working on a deck, the proper washing order would
be to start with the outside railings, then the inside of the railings,
followed by the floor, and finishing with the steps and any posts
underneath the deck. When working on a fence work in sections,
and when working on wood siding do one side at a time in its
entirety.
17. Begin washing with the lightest pressure possible.
Between 300 PSI and 1000 PSI, depending on the cleaner you
are using and the condition of the wood. Begin by pulling the
trigger with the wand aimed out towards the yard. Always begin and end your wash stroke “off the
wood”. Wash in the same direction as the wood grain, lifting up at the end of each board to aim
the water out into the yard again in a golf-stroke finish. Try to wash the entire le3ngth of a board
in one motion, rather than to wash in three-foot strokes. (This eliminates the ‘stop & start’ marks,
or “zebra stripes”).
18. Wash using the wand in a fixed position in relation to the wood, at approximately 90º to the
surface being cleaned.
19. Rinsing is one of the most critical steps in any deck job. The wood is porous and the action of
washing the deck drives the detergents deep into the wood. Rinse until no sign of sudsing can be
detected. Soap residue will affect the ability of the wood to accept the sealer, so a poorly rinsed
deck often leads to early failure for the sealer.
20. If you used a sodium hydroxide-based stripper or a bleach-based cleaner to wash your deck, you
must neutralize the wood when you are done cleaning. The pH of these chemicals is very
alkaline. This alkalinity changes the pH of the wood drastically and may affect the ability of the
sealer to bond to the wood. In cedar and redwood, this change in pH turns the wood black.
Neutralizing the wood with oxalic, phosphoric, or citric acids will bring the pH back to normal as
well as brighten the wood. Neutralizing
with a commercially-prepared proprietary
blend of these acids creates better
results. Allow the brightener to dwell for
10 – 20 minutes and then rinse it off. If
you don’t rinse off the brightener, you
may experience what we call the white
powder effect.
21. After
cleaning
the
deck
thoroughly, be sure to rinse off everything
near the deck - such as plants, house
siding, windows - and be sure to rinse the
house siding, windows, and patio below
the deck as well. Little bits of wood fiber
have been loosened by the cleaning
process. If these bits are allowed to dry
on siding or glass surfaces, they become
© 1999 - 2010, Contractors Foundation
23
extremely difficult to remove later.
The appearance that you will ultimately end up with on any wood
is only as good
as the preparation work
you put in during the washing process.
Now is the start of your job clean-up.
22. Pump unused liquid back into containers, never onto the yard.
23. Rinse sprayer clean with water after each use.
24. Rinse all plants and grass after removing tarps.
25. Pressure wash driveway (if work order calls for it).
26. It is now time to pack up equipment and clean up. If you will be back within a few days, it is best
to leave items off of wood surfaces to allow for proper drying. Always inform the customer why
you are not putting items back. Examples would be deck furniture, plants, thermometers, etc. The
washing and rinsing process is now complete. You will have to let surfaces dry for approximately
48 hours before sealing.
27. Place marketing messages – lawn signs, door-hangers, etc.
28. Move on to the next job.
© 1999 - 2010, Contractors Foundation
24
SKIP THE CLEANING?
Cleaning outdoor wood is the required first step for any wood renewal project. A customer who is trying to
save money might ask you to seal without cleaning. Educate this customer about your process. If the
customer insists on proceeding without washing the wood, you might be wise to walk away from the job.
Sealing wood without cleaning it first is like dying dirty clothes. The initial look will never meet your standards,
and the long-term effects are worse.
An exception to this rule might be reasonable for brand-new wood fences. People tend to judge the
appearance of their fences from quite a distance, and contractors have sealed NEW fences without washing
them – and gotten satisfactory results. Fences are vertical surfaces, which means that Mother Nature is
gentler on them than she is on decks.
On the other hand, people judge the appearance of their decks from close-up. Decks are horizontal surfaces
that catch the full brunt of weather. Washing decks before sealing is essential.
Cleaning the wood is the right preparation for sealing. If done well, the end results will be beautiful. If done
with a mediocre attitude, more work has to be done to get an acceptable result. If done poorly, damage to the
wood can occur.
DEVELOP GOOD HABITS!
Following orderly procedures and making them a
habit - every time on every job - will help you save
time, save materials, and avoid mistakes, forgotten
areas, and other problems. When washing or sealing
a deck, follow this plan: 1) Do the outside of the
railings first. 2) Then move to the inside of the
railings. 3) Proceed to the floor, the stairs, and finally
any posts under the deck.
Sometimes exceptions are necessary. When
stripping a deck, for example, you might want to
modify this order for safety purposes. After
applying the stripper, you might clean the floor first
to minimize the danger of slipping. Then move to the railings and finally the stairs and posts under the
deck. This method leaves the stripper working longer on the handrails, which need more time (because
they are vertical surfaces).
© 1999 - 2010, Contractors Foundation
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CLEANING NEW WOOD
If the wood was never sealed, the best cleaning product is a percarbonate cleaner.
CLEANING WOOD THAT PASSES THE SPLASH TEST
The best cleaning product is a percarbonate cleaner. It may also be acceptable to use a bleach mixture or a
highly-diluted stripper.
If sodium hypochlorite (chlorine bleach) is going to be used, special techniques are called for. First, the
solution should not be stronger than 1% - 2%. 1% is the best concentration for cleaning most surfaces.
This ratio can be accomplished by mixing one gallon of 5% household bleach (or one of the new, smaller
containers that come with 6% bleach) with one to six gallons of water. Remember that bleach alone does not
clean wood, so a surfactant (detergent) must be added. We recommend adding 4 oz. of a low-sudsing liquid
cleaner to the diluted bleach solution (not dish detergent).
Every deck cleaned with an alkaline (like chlorine bleach) must be neutralized with Wood Brightener.
CLEANING WOOD THAT FAILS THE SPLASH TEST (stripping)
If there is existing sealer on the wood that is not fully spent, the approved cleaning product depends on the
previous sealer used. A “Test Patch” will help you determine the best product to use. The best time to do a
Test Patch is at the time of the estimate. Before you quote a price, know what you are cleaning.
A Test Patch Kit consists of a pail with a spritzer bottle of a strong caustic stripper, a spritzter bottle filled with
a wood brightener, and a scrub brush. Select a spot on a vertical surface that gets no sun and another spot
on the floor where the sealer appears to be worn.

Fill the pail with a little water.

Spritz caustic stripper on the two surfaces and allow it to dwell for several minutes.

Agitate with the scrub brush.
If the sealer “melts” (turns into goo, as opposed to coming off in strips) then the old sealer was an oil that can
be stripped with sodium hydroxide. If the old sealer doesn’t move (or if it comes off in strips) then the old
sealer is a water-based product and a special stripper is needed.

Rinse the spots with water.

Neutralize with the brightener
Every deck cleaned with an alkaline must be neutralized with Wood Brightener.
© 1999 - 2010, Contractors Foundation
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BRIGHTENING AND NEUTRALIZING
Brightening the wood after cleaning is a critical step as well. The high alkaline content of the detergents have
left the pH of the wood out of balance. Wood brighteners restore the pH to neutral.
The wood brightener/neutralizer has an amazing effect on the finish job. Depending on the type of wood, you
should see the wood lighten and brighten right before your eyes as you spray this on. This is one process
that is usually skipped by less-professional contractors, and this is one of the many reasons why
professionals like you get better results.
AFTER STRIPPING
AFTER BRIGHTENING
DRY & READY FOR SEALING
© 1999 - 2010, Contractors Foundation
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Deck Cleaning Flow Chart
Splash Test
(Determines if sealer is present)
Never Sealed
(Gray, weathered)
Previously Sealed
(Weathered, dark, some old sealer visible)
Test Patch
Oil-based
(Semi-transparent, solid color)
Wash
(Percarbonate or
bleach deck wash)
Strip
Water-based
(Acrylics, latex, etc.)
Strip
(Caustic stripper)
Wash
(Solvent-based or
stripping pastes)
Rinse
Rinse
Rinse
Neutralize/Brighten
Neutralize/Brighten
Brighten
(Acid or Blend of acids)
(Acid or Blend of acids)
(Percarbonate
or bleach deck
wash)
Rinse
(Acid or Blend of acids)
Dry
Dry
Dry
Dry
Seal
Seal
Seal
Seal
(With whatever was
on before)
© 1999 - 2010, Contractors Foundation
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TIME WASTERS / TIME SAVERS
Carry everything you might use on the job every day. If you don’t, you will surely need the one thing you
didn’t bring.
Plan your route and group your customers geographically.
Never make a trip to or from your vehicle without carrying something.
Prepare for clean-up from the first moment on the job.
Establish barriers to minimize clean-up – tarps, mineral
spirits, water, backdrops, etc.
Call ahead to assure that water and power are on and
dog is leashed.
Test your tools before setting out in the morning. Bring
back-up tools with you.
Clean up tools and the job before material dries.
Wash in the morning, seal in the afternoon. The wood
is always drier in the afternoon.
You can wash in the rain.
Establish productivity standards. If a 12x16 deck with a full set of stairs is the “standard” deck, plan to
wash a deck like this in 60-90 minutes (one person) or in 45-60 minutes (with two people on the job). Seal
this deck in 90 – 120 minutes with two people, or take about 2.5 – 3 hours by yourself.
© 1999 - 2010, Contractors Foundation
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TROUBLE-SHOOTING PROBLEMS
Extractive Bleeding
Extractives are natural chemicals found in the wood where the sapwood transforms into heartwood.
Extractives like tannins provide the resistance to insects and decay. Most extractives are dark in color, but
some are light-colored. Extractives are transported to wood surfaces when free water is present. When
the free water evaporates it usually leaves a reddish brown stain or discoloration. This is called extractive
bleeding.
Pitch and Resin
There are also non-water extractives such as pitch or resin. Resin is a fluid that exists in conifers (mostly
pine). Resin will leach to the surfaces of the boards. Wood that shows resin at the surface, whether kilndried or not, should be replaced as it will continue to leach this resin. When the resin reaches the surface
it will harden, appearing as a whitish stain that follows the grain pattern.
Many of the softwoods will have a concentration of resin around knots. This can cause paints and stains
to turn yellowish brown over knots. This is better known as knot bleeding. Resins cannot be sanded out or
removed from the wood, so replacement is the only option. This is something that should be explained to
a customer and is an opportunity for up-selling.
Furring and Fuzzing
These two terms are interchangeable and are often confusing. We will define and differentiate the two
terms. Applying too much pressure to the wood surfaces causing damage causes furring. On some
species of softwood some furring may occur however it should be minimal. Fuzzing on the other hand is a
chemical reaction. This occurs when a high alkaline chemical removes lignin from the wood. Lignin is the
glue-like substance that holds wood fiber together. Fuzzing and furring must be addressed before
applying a sealer. If boards are furred they must be sanded prior to sealer. Fuzzing must also be
addressed which there are many methods to remove fuzzing. These include the use of a buffer and pad,
green scrubbies, sandpaper, stiff nylon bristle brushes, extra rinsing, and so on. These will be discussed
during the class.
Rust (Iron) and Tannin Stains
These stains can be removed by using an acid base neutralizer. Brightener is recommended. Allow to
dwell on wet surface. Rust stains and nail bleeds usually occur when using non-galvanized nails and
hardware. The professional wood restorer will remove these stains and not apply a sealer over them.
Checking, Cracking, and Warping
A separation of the wood cells along the grain is a result of uneven shrinkage or water damage. Cracks
that run parallel with the grain are a sign of drying out (shrinkage). Cracks that run against the grain are
called checking and are usually a sign of water damage. Checks are most commonly found on wood
surfaces where the grain is wide or on the ends of cut pieces. Another result of uneven shrinkage is
warping which is a distortion of the wood from its intended shape. All wood should be evaluated before
sealing or addressing repairs. Keeping the wood surfaces protected minimizes checking, cracking, and
warping.
Mill Stamps
Mill stamps are the marks put on the wood surfaces at the mills. Mill stamps contain information about the
wood and its quality. Mill stamps cannot be removed unless sanded. A word of caution: when removing
visible mill stamps with a sander, it will change the texture and characteristics of the wood surfaces. A
professional will keep this in mind as detail or excessive sanding will cause a blotchy and shiny finish. It is
best to sand all surfaces or “feather in” the sanding to result in a consistent finish
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Grease
These stains will often occur around the “grill area”. The best way to remove these stains is to treat with a
degreaser first. Apply degreaser, scrub, allow to stand and then rinse. As with other areas of concern with
wood appearance a stain or sealer will accentuate or magnify imperfections in the wood. Keep this in
mind when working with grease stains, as once the sealer is on the wood it is a huge task to fix these
areas
Discoloration
This is the first noticeable sign of degrading wood. For light wood species the surfaces will darken and
dark wood species tend to lighten in color. As the wood continues to weather, the surface will then gray.
This graying is caused by mildew growth and the cellulose left as the colored extractives and lignin
degrade. It is these loose fibers that need to be removed before sealer. UV rays play a large part in the
graying and discoloration of the wood. In most cases the proper techniques and chemicals will restore the
wood to its natural color and tone.
Mill Glaze
Mill Glaze is defined as a condition of wood where the cells are “glazed” shut. It is believed that excessive
heat to the surfaces cause mill glaze. The use of dull blades by the sawmill, or use as they dull, is often
blamed for causing this heat. Now that mill glaze is defined we have the question of does whether or not
mill glaze actually exists. In tests conducted by the Forest Products Laboratory a division of the United
States Department of Agriculture, they have not been able to duplicate mill glaze in testing nor have they
been able to prove its existence in investigated mill glaze reports. While they do not say that mill glaze
does not exist they have not been able to prove that it does. It is recommended that a “splash” test be
conducted on all surfaces. A splash test is when water is sprayed on the wood surface then look for any
repelling or beading. If this occurs there is something on the wood surface that will need to be removed
before sealer. A splash test should be performed on ALL surfaces. Even a very grayed surface may
appear only weathered when in fact may have a sealer. It is further believed that “mill glaze” failures can
be explained by one of the previously mentioned characteristics. Regardless the existence of mill glaze or
not it is very important that a splash test be conducted on all surfaces. If wood is coated that had any
substance that prevented adhesion it will cause a blotchy appearance as well as not hold up to
expectation. Having to re-strip a job will not only be bothersome but will affect your image with the
customer and more importantly cause you loss of money on the job.
Black Stains
The black streaks left behind from dripping rain are often noticed on the surface of gutters. They also appear
on the underside of decks. A caustic like bleach, applied and allowed to dwell for a short time will minimize or
eliminate these.
Melted Wax
Candle wax is a common but difficult problem on decks. Scrape the excess wax. Liquefy the remaining wax
carefully with a heat gun and try to absorb the liquid wax into a soft towel.
Leaf Stains
Leaves that contain tannins (i.e.oaks, etc.) will leave a stain on any wood over time. Brightener is the best
solution for this problem.
Algae & Mildew
Common problems. All caustics will attack algae and mildew effectively.
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SAFETY ISSUES
Before starting any job, familiarize yourself with all OSHA recommendations. Safety is an area that we
often ignore, until we learn an unfortunate lesson. Sometimes we are in a hurry, sometimes we believe
that we are invincible, sometimes we just don’t think. Make safety a habit! In this business, we deal with
several safety issues all the time.
CHEMICALS:
Chemicals are a large part of our daily lives in this business. We use chemicals to do all the work and
save us time, and sometimes it is easy to forget just how dangerous they can be if we get careless. Make
it a habit to always wear skin and eye protection when transferring chemicals from one container to
another and whenever using these products. Always follow the manufacturer’s instructions when mixing,
handling, diluting, or applying chemicals.
Be aware of the health risks of the chemicals you use by
studying the MSDS your supplier will provide to you. MSDS
sheets offer important information on chemicals. These
sheets must be with the chemicals being used and available.
If you have chemicals in the vehicle then the corresponding
MSDS sheets must be in the vehicle. The content of the
sheets include chemical and
safety information. Keep a copy of this MSDS available on the
job for your protection. Always read and follow the directions
listed on the label, too.
Plan what to do in a chemical emergency. If a caustic like
REMOVE got on your hands, for example, you could
immediately stop the corrosive effect by applying some Wood
Brightener to the skin. A plan like this won’t work for eye contact, though, so you should keep eye wash
cups and sterile water handy. Be prepared.
SLIPS AND FALLS:
This is the most common injury on the job for deck guys. Many of the cleaners you will use every day
include detergents. They can make the surface you are standing on very slippery. This is particularly
dangerous when standing high in the air or on stairs. Warn your employees to minimize walking on any
surface until you are satisfied that it is fully rinsed and safe.
Inadequate rinsing, for example, could lead to a residue that would be re-activated at the next minor rain.
This is a great danger to your unsuspecting customer. Inadequate rinsing is a serious danger and will
also cause most sealer applications to fail. Be certain that you rinse completely when you are done
washing, and warn your customer to be careful until you’re done with the job.
HEIGHT:
Many decks are two-story structures. Even though most of these have stairways and handrails, you must
remain aware of your surroundings at all times. Seasoned professionals have, in a moment of lost
concentration, walked off of scaffolds and fallen to the ground. Don’t let this kind of accident happen to
you.
When using a ladder, care must be taken to plant the ladder well and to tie it off at the top. Having a
second person foot the ladder is a wise precaution. NOTE: Sealer can build up on ladder rungs, so take
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time regularly to clean ladders and keep them safe to use.
A damaged ladder should be destroyed instead of being repaired. If you repair a ladder, the manufacturer
is no longer liable for the performance of that ladder.
Always select ladders of adequate length and weight rating. Extend your ladder so that it goes at least 34’ higher than the surface it is resting against.
The proper angle for using any extension ladder is automatic if you follow this simple guide: When the
ladder is positioned, you should be able to stand at the base of the ladder and extend your arm straight
out. If your hand just reaches around the rung that is even with your shoulder, the angle is correct.
ELECTRICITY:
Water and electricity don’t mix well. Avoid spraying liquids around outlets and junction boxes.
When you first look at a job, note any overhead electrical wires. Metal ladders provide an instant path to
ground, and you can be fried to a crisp in seconds.
SPRAYERS:
Never store pump-up or mechanical sprayers under pressure.
RAGS:
Used rags will spontaneously combust in a closed area. Store in an air-tight container. Never leave rags
in a pile in your truck or garage. Consider using paper shop towels and dispose of them to avoid this
danger.
TOWING TRAILERS:
If you use a trailer to carry water, tools, materials, etc. be sure that it is set up properly. A trailer should be
balanced with 10% of the total weight carried on the tongue. If the load shifts, the trailer will be out of
balance and could cause you to lose control of your vehicle.
VAN LOADING:
If you use a van as your work vehicle, be advised that, under heavy acceleration or braking, items will
shift and/or start flying around inside the van. Always secure your materials and tools, and leave nothing
loose that could injure you while driving.
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READING MSDS PAGES
Always have a copy of the MSDS (Material Data Safety Sheet) on the job for every chemical you have
with you, and always follow any warnings and instructions.
MSDS pages are OSHA’s way of protecting you by giving you the key information you need when
handling any chemicals. The first time you use any product, no matter what the source of that product is,
you should always carefully read the MSDS page.
These sheets do not follow a specific format, so you will have to examine each one to find out the
important points.
MSDS pages will identify the chemical involved and describe its properties (i.e. hazard to health,
flammability, etc.). Somewhere on the sheet, you will find an explanation of how the product can affect
you, and what you need to do if you come in contact with the product.
In addition to handling procedures, the MSDS will also address storage procedures.
ALWAYS have a copy of the MSDS with you for every product you are carrying in your vehicle. In the
event of a traffic accident involving any spillage, you must be able to provide the critical information
needed by emergency personnel.
NEVER ignore the safety precautions cited on the MSDS page or on the product label. These warnings
are intended to prevent injury and long-term damage resulting from misuse of the product.
NOTE: Many products we use require few warnings because the products are not deemed hazardous.
NOTE: International Safety Cards are now issued by many manufacturers as a replacement for MSDS
pages. The information contained is similar, and the format of the cards is more uniform.
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CONCLUSION
This concludes our study of cleaning wood exposed to the elements.
There is no substitute for years of field experience, but we have covered every topic in this class that you
need to know to be recognized as a professional wood cleaning specialist. Please retain this manual as a
Reference Guide.
The others taking this class are an important resource for you. Network with these other professionals to
maximize the benefit of taking this class. Your instructor also has an interest in your success, so stay in
contact with him as well.
We wish you success in your business. Business owners are a special breed. They carve their living out
of their own ingenuity and hard work. We salute all of you.
To complete your knowledge about cleaning and sealing decks, you should enroll in our deck sealing
class while all of this information is fresh in your mind. Once that class is completed, you will be fully
prepared for your chosen profession.
Certification is available to you at any time. The material included in the Certification test is fully covered
in the Wood course and in the Manual associated with these courses. This independent Certification sets
you apart from your competitors in a way no manufacturer-sponsored certification can.
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Section II – SEALING
SEALING
Before we can think about sealing any wood, we have to ask ourselves a few basic questions:
IS THE DECK DRY? YOU GOTTA HAVE A MOISTURE METER!!
If you are using a penetrating oil sealer the wood must be properly dry before you can seal it.
If the moisture content of the wood to be sealed is too high, the sealer won’t penetrate as
much as it should. The result will be sealer that dries on or very near the surface of the wood.
Obvious signs of wood that was sealed before it was dry are traffic patterns worn into the
finish over time. Since the product is not designed to be a coating, it will fail when we make it
into a coating.
If the moisture level of the wood is left up to individuals to determine, each of us would have a
different opinion of whether or not the wood is dry enough to seal. Until you develop a real expertise in this
area, we recommend that you invest in a moisture meter.
These instruments can probe the wood and report the percentage of moisture. Most oil sealers recommend
that the moisture level in the wood be 12% or less before sealing. Be sure to probe in several different areas
of the typical deck, because areas exposed to full sun are dry long before areas that are shaded for even a
small time of the day. You don’t have to probe deeply, either. In most cases, the sealer does not penetrate
deeper than a few millimeters so the wood only has to be dry for the first few millimeters.
We recommend not sealing wood early in the morning for the same reason. Morning dew can prevent the
proper absorption of sealer. Decks that are too wet at 8:00 AM may be ready to seal by noon. NOTE: Decks
stay wet longer when they are close to the ground Docks over water can take quite a bit longer to dry as
well.
IS DECK CLEAN?
Make sure there are no traces of mildew or dirt on any surface you intend to seal. Sealing over mildew
doesn’t do the wood any good. If you stripped the deck, be sure to check that the wood passes the splash
test before you apply a new coating of sealer.
We do not recommend that every deck be stripped to bare wood before re-sealing. Often, particularly when
performing maintenance on wood, we need to merely add another coat of sealer.
WHAT FINISH DO WE WANT TO USE?
Which sealer is the best? The choice of sealers can be difficult. This debate is likely to continue for years, as
well it should. As science progresses, so do the sealers.
Sealers come in many forms. Some are oil-based, some are water-based, and some are even made of
acrylic. Some are transparent stains, some are solid stains. Some sealers are made to coat over a surface,
others are made to penetrate the wood.
Sometimes the customer will want to choose the finish. Their decision may be based on their own
experience or a commercial they saw on TV. You are the expert, and should try to stick with the products
you use all the time. Educate your customer on why you use the sealer that you do, and they’ll appreciate
your expertise.
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HOW DO I CHOOSE?
Sealers are made from a number of different bases with a variety of added chemicals. Some adders
make the sealer perform better (application, bonding, flow, penetration, etc). Other ingredients simply add
bulk. Let’s define some of the ingredients and characteristics of today’s wood products.
It should be understood from the beginning that there is no perfect coating. There is a stain, sealer, or
coating that is ideal for each and every situation, however. Most people consider staining wood to
meaning adding a color to it without hiding the grain. Many things can go wrong when staining that
include, but are not limited to, blotchiness, bleeding, improper adhesion, colors and tones that are not the
same as samples, fading, and so on. Unfortunately it does take experience and knowledge along with
much trial-and-error to become a true professional. There is not a one coating that is best for all surfaces.
There are advantages and disadvantages to each.
Part of the selection process has to involve the customer. Be sure that any concerns the customer may
have are addressed during this selection process. For example, are appearances most important? If so,
are they going to keep up with the maintenance of the project down the road or do they expect to be able
to ignore this job for the next ten years? As the professional, it is up to you to recommend the product that
is to be used. The customer should be more involved in color selection than selection of the actual
product.
PENETRATING STAINS AND SEALERS
Penetrating stains may have pigments and contain oils. These stains penetrate into the wood and do not
form a surface. Properly applied these products do not blister or peel. Semi-transparent oils will allow
wood grain to show through. The life expectancy of these products is approximately 2 years on
horizontals and 4 years on verticals. Semi-Transparent Stains will last slightly longer than water repellent
preservatives and sealers.
WATER REPELLENTS AND WATER REPELLENT PRESERVATIVES
Penetrating finishes are separated further into Water Repellents and Water Repellent Preservatives.
Water Repellent Preservatives contain mildewcides or fungicides, which differentiates them from simple
Water Repellants. These finishes contain 10-20% Binder (varnish, linseed oil, drying oil, tung oil), a
solvent (turpentine, mineral spirits, water, etc.), and a substance that repels water.
SEMI-TRANSPARENT STAINS
These coatings are somewhat of a compromise between a sealer and a solid stain. These finishes are
available in both water and oil base. An oil-based semi-transparent stain will penetrate the pores of the
wood and should not form a film on the wood surfaces. A water-based semitransparent stain will not
penetrate the wood surface and will form a film which will peel and flake. “Semi” means half and that is
what a semi-transparent does, it hides about half of the grain and characteristics of the wood. These
coatings tend to last a bit longer than sealers before maintenance coats are needed. There is generally a
much larger selection of colors and tones when moving to a semi-transparent, from a sealer. This is
usually a nice alternative for one who wants a certain color but still wants to see some grain through.
Another favorable application for a semi-transparent is when wood is getting older and has discoloration
and blemishes that are a natural part of the decomposition process. A semi-transparent will help to give
the wood a more uniform appearance.
SOLID LATEX STAINS
These stains are thicker film forming and have a heavier solid content than water repellants. This means
they are more durable and longer lasting. It is recommended to use two coats with the finish being a
primer coat, follow manufacturers recommendations at all times. Latex solids are more flexible than oil
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based solids. The value of latex on the exterior is that it is permeable and allows for water vapor to pass
through. Latex products have reduced solvent content and clean up with water.
PERMEABILITY
Sealers are permeable, which means that they allow the wood to “breathe”. This means that ordinary
humidity can enter and leave the wood during the normal cycle of the day, but droplets like rain cannot
enter the wood. The more pigment the product contains, the less permeable the sealer is. A quality
permeable sealer will allow sap to exit the wood without damaging the sealer as it passes through.
Paints are non-permeable, which is why painted decks crack and peel drastically after a short time.
Ever notice what happens to latex paint on a window sill? The humidity present in the wood tries to
escape when the sun hits the wood and raises the temperature. Since this moisture cannot pass through
paint, the only natural result is that the humidity pushes the paint off of the surface of the wood to escape.
That is why paint cracks and peels. This result happens most frequently on window sills (horizontal
board) rather that on vertical window trim, because the top end of a vertical board is usually not painted
(allowing the humidity to escape). This is why we NEVER paint a wood deck.
VOLATILE ORGANIC COMPOUNDS
For many years, manufacturers threw out terms like “percentage of solids” as a selling point for their
products. In layman’s terms, this refers to the amount of product that remains in the wood after everything
that evaporates is gone. What evaporates are called “volatiles” or “VOCs”. The EPA has been tightening
regulations on VOCs for years because they harm the quality of the air and the ozone layer. Many sealers
have had to reformulate once (or several times) to meet these changing regulations. Every time a
manufacturer reformulates, the product characteristics change.
VOCs are often simple mineral spirits or turpentine.
NOTE: “High solids” does not mean that the product is thick. One brand with the highest solids of any oil
sealer we know of is also one of the thinnest oils you will ever work with. It simply doesn’t contain much
volume of VOCs.
Sometimes sealers contain manufacturing by-products that manufacturers want to dispose of, such as
benzene. A careful examination of the MSDS will reveal a lot to you.
WATER-BASED FINISHES
Water-based finishes are becoming more popular as society’s concern over the environment has
increased. Many states are changing laws that limit the amount of solvent or volatile organic compounds
(VOCs) a finish or paint may contain. A water-based finish usually has acrylicor polyurethane dispersed in
water. After the water evaporates the droplets of the stain interlock, as the solvent evaporates a film is
formed. Water-based products are film-forming finishes. Water based products and acrylics are very
difficult to maintain and to work with.
OIL-BASED FINISHES
Oil-based finishes are penetrating finishes. It is a myth that oils penetrate the wood and protect from the
inside. What oils do is penetrate and fill the wood cells which will prevent shrinkage and swelling from
water-vapor exchange. These finishes do not protect the surface like a film-forming finish. You should use
caution when applying oil-based finishes as improperly applied oils can become a food source for mold
and mildew.
OIL BASED SOLID STAINS
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These are also film forming and have a heavy solid content. They are less flexible than latex based
products and more likely to crack, flake, and peel. It is recommended to use two coats of this type as well,
with one coat being a primer. This is a more permanent decision and will not be easily maintained in the
future.
PAINTS
Paints have the highest content of solids and are also film forming. They prevent weathering and will hide
much of the woods characteristics. Latex paints are the most fl exible. One way to consider the difference
between paint and a solid stain is that the solid stain is a “weathered down version of paint.”
LINSEED OIL
Linseed oil is one of two straight oils most often used. Linseed oil, available raw or boiled, is related to
vegetable oil. In wood restoration we use boiled linseed oil which cures much faster than raw linseed oil.
It is often known as flaxseed oil which comes from the seed of common flax. Linseed oil is a drying oil that
hardens when exposed to air. This is why it is used in many sealers, stains, paints, varnishes, and
coatings. Linseed oil sealers tend to be coatings to some degree, and as such they require weather
cooperation during application. Most of these products carry directions like “Do not apply if you expect
rain within 24 hours” and “Do not apply if the temperature is expected to drop below 54º F within 24 hours
of application”. The coating provided by linseed oil sealers adds appearance and durability, but can
potentially show traffic-pattern wear on the surface over time.
TUNG OIL
Tung oil is the other straight oil used. It is actually taken from the nuts of the tung tree, which was
originally found in China. One of its more favorable characteristics is that it is one of the most waterresistant oils. This is why it is found in many paints and coatings. Used by itself as a protective coating it
is too thin and cures very slowly. This is why it is often an ingredient in coatings and not used as a stand
alone product.
PARAFFINIC OIL
Paraffinic oil is produced from crude petroleum and is related to kerosene. When raw crude oil is left to
dry it separates into a wax and oil. The wax is called paraffin wax and is used in less expensive sealers
and candles. The oil is paraffinic oil and contains no organic nutrients and will not attract or support the
growth of mold and mildew. Paraffinic sealers tend to be penetrants rather than coatings. They require
little or no weather cooperation. Some brands state on the label that there are no weather or temperature
limitations on the application. These sealers are usually not fussy applications because they tend not to
show either lap marks or drips. These products are very fussy when it comes to the moisture content of
the wood, however, because excess moisture prevents proper penetration. Oil and water just don’t mix!
PARAFFIN WAX
These are short life-expectancy finishes that leave a residue that is temporary. These are generally the
less expensive finishes that will be used more than once a year.
NATURAL OILS
Some woods contain a heavy content of natural oils. Teak, rosewood, cocobolo, and others contain
natural oils that can inhibit the drying of oil-based finishes. In these cases it is recommended that the
wood surfaces be wiped with acetone, lacquer thinner, or naphtha. These are fast drying solvents that will
temporarily remove the natural oil to allow the oil- based finish time to bond and cure into the wood.
STAINS
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In most cases we are dealing with pigmented stains. Pigment stains require three important ingredients,
pigment, a binder, and a carrier.
PIGMENT
Pigment is a finely ground, inert, colored powder. In most paints and stains these are iron oxides. Iron
oxides can be natural or synthetic with the natural iron oxides being ideal for wood stains and the
synthetic iron oxides being more opaque. In most sealers, it is the iron oxide pigment which gives it UV
protection. The UV rays of the sun are reflected away from the wood by these minute particles of color.
Over time, the rays of the sun use up the oxide particles, and the wood begins to gray once that has
happened.
BINDER
Binder is basically the “glue” that helps the pigment adhere to the wood surfaces. Pigment will not adhere
on its own and needs a binder. Binders include oils, alkyds, urethanes, acrylics, lacquers, and waterbase.
CARRIER
A mixture of binder and pigments are too thick to apply so a carrier is needed. The carrier is a solvent
which is compatible with the binder. Mineral spirits, acrylics, and urethanes are examples of carriers.
SOLVENT
A solvent dissolves a cured finish by turning a solid into a liquid (melting).
THINNER
A thinner just thins a liquid. One substance can be a solvent for one finish and a thinner for another or
possibly a solvent and thinner for the same finish.
COATING VS. PENETRANT
Oil sealers may contain any of several kinds of oil. Oil sealers may be coatings or penetrants or some
blend of both characteristics. Pure coatings sit on top of the wood. Pure penetrants sit at and below the
surface of the wood. A sealer that leaves any kind of surface coat on the wood is considered a coating,
whether that is minor (i.e. 10% coating, 90% penetrant) or a full (100%) coating.
Generally speaking, coatings hide flaws in the surface. The closer they are to being solid color stains, the
more they are able to hide flaws. They may be subject to visible wear in traffic areas as well. Coatings
should be stripped before applying a new layer because they will not allow new layers to penetrate into
the wood and bond to it. Most coatings require careful application, because flaws like drips and runs will
show in the final job.
Generally speaking, penetrants won’t disguise flaws in the surface such as a poor wash job or stains.
Penetrants do not show any traffic pattern wear. They normally do not have to be stripped to recoat down
the road, either, because the new sealer penetrates through the old coat and bonds directly to the wood.
Applications of full penetrants are fully forgiving, which means that drips or lap marks will not show.
LIFE
Most sealers are designed to last approximately two years on the horizontal surfaces and four years on
the vertical surfaces. Some claim more, some make no claims at all. Customers will usually ask about the
life of the product you are suggesting, and it is important that you know that the answer to that question is
“Depends…” The life depends on the sealer, the location of the deck, the condition of the wood, the local
weather conditions, the use of the deck, etc. Remember that sealers are never guaranteed to ‘look good’
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for any amount of time. They are only guaranteed to repel water for a period of time. Manufacturers are
notorious for not standing behind their products. They simply blame a poor application by the contractor
and leave you holding the bag.
Some manufacturers sell “lifetime” or “25-Year” finishes. These are almost always water-based silicone
products. Silicone is an excellent water repellant, and lasts a long time. It cannot ever be fully removed
from the wood later on, so selecting one of these products is a permanent decision. The drawback to
these products is the UV protection, which often fails within a few years of the initial application. Once the
wood starts to turn gray, the nightmare begins. If you can’t strip the product off, how do you get down to
the wood to clean it and add more UV protection? There is no answer.
SURFACE PREP & pH
Your choice of sealer affects your cleaning method. For example, most oil sealers prefer an acidic surface
to bond to. Washing with an alkaline cleaner and finishing with an acidic brightener will leave a perfect pH
surface. Most water-borne sealers prefer an alkaline surface to bond to. Washing with an alkaline cleaner
will leave a perfect pH surface. If you want to brighten the wood, you can do that the same way we talked
about before as long as you finish with some sort of alkaline rinse.
If the sealing portion of the job is delayed (for any reason, but usually because of a rainy period)
SO, AGAIN, HOW DO I CHOOSE?
The answer to this question is simple: Find a sealer that is fast and easy to apply so that you minimize the
application time and maximize your profit. Make sure that the customer likes the color while you are at it.
Next, make sure that it has the longevity that the market demands, and while you are checking all that
you should also make sure that it can be easily maintained and stripped when necessary later on.
Some words of wisdom: While there is no perfect single product out there, there are products that will
work well for you on most of the jobs you will face. Depending on the types of wood you deal with in your
area, the typical weather factor in your area, and the customer-accepted appearance predominant in your
area – there is a sealer that will handle most of your jobs.
It is an excellent idea to minimize brand-hopping. Each product has its own characteristics, and changing
products can mean changing your cleaning products or techniques, too. The challenge to be perfect on
every job gets to be impossible if you change products on every job. Sticking with one primary brand for
80% of your work is a good decision that will help you become an expert with that product. Keep your
knowledge of all of the other products in your back pocket so you can switch products to meet the
demands of a tough or unusual job, but go right back to the sealer you are most experienced with for the
job after that one.
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THE NEXT BIG DECISION
We will now go over the different ways to apply products. For quality and lasting results it is
recommended to use a brush method. For speed and ease, spraying works best. There are times when
different methods are more beneficial. Let’s discuss all accepted application methods.
BRUSH METHOD
White china bristle brushes are recommended and are the most efficient kind to use. By the way, these
brushes are not actually made in China. They are really hog hair bristles, and the white ones work better
than the black ones. This type of brush is soft and holds a lot of product. It is also easy to “work” this type
of brush. These brushes tend to be more expensive but are a must for the professional wood restorer.
Back brushing is important for most applications to smooth out areas, runs, and drips, these brushes are
ideal for back brushing. “Back brushing” is going back over your work to eliminate inconsistent and
needed areas.
SPRAYER METHOD - AIRLESS
An airless sprayer produces fine droplets. Fine droplets allow quick-dry products like latex paint to dry
faster. For oils, fine droplets may become airborne more easily and cause problems. Sprayers are an
excellent choice for multiple-layer surfaces (board-on-board fence, lattice, etc.) and for labor savings.
Proper care and preparation are very important to prevent incidents caused by overspray. Any overspray
should be cleaned immediately with the proper cleaner. These sprayers can be adjusted to apply a very
light coat. You should monitor how much your coverage is per gallon as to apply the correct amount of
product as per manufacturer recommendations.
SPRAYER METHOD - POWERED DECK SPRAYERS
Powered deck sprayers have pumps that provide air to apply the product. They are used both for
chemical application as well as applying sealers. They produce a medium size droplet and are not
recommended for applying paints and solid stains. The pumps are high volume, low pressure (HVLP). It
is a good idea to have an extra pump for a back up if one fails. If you have a back up you will not lose
time or a days work as these are easy and quick to replace on the job.
SPRAYER METHOD - PUMP UP
This sprayer produces a large droplet and is more recommended for chemical application than applying
coatings. These sprayers produce uneven patterns as well as different volumes as the pressure drops
between pumps. This is the least expensive sprayer to purchase however you will be purchasing quite a
few over time.
ROLLER METHOD
The roller method is more popular among homeowners. As with painting you will need to go back and
forth over an area to ensure proper coating. This method provides a very inconsistent finish and it is
difficult to control lap marks. With thin coatings, the sealer is often “flung” by the roller to surfaces you
never intended.
LAMBS WOOL, PADS, MITTS, ETC.
These are other tools that contractors use to apply product. All of these products have advantages and
disadvantages. Flat stain pads are very convenient for back-brushing, and can be used for secondcoating a water-borne sealer, for example. All of these methods work much better on new or smooth
surfaces. Older, rougher surfaces may be challenging. When using a mitt it is recommended that a
second glove is worn to prevent splinters from attacking you.
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APPLY WITH CARE!
Whether using a water or oil based product it is important to be careful in applying it.
• Watch for lap marks.
• Pay attention to weather forecasts and drying times. Use of moisture meters to determine
moisture content of wood is essential and a must for the wood restoration professional. The
general rule of thumb is that the wood should contain a moisture level no greater than 12% - 15%
before applying a finish.
• Wood surfaces that have been exposed for 2-4 weeks or more should be evaluated for recleaning of surfaces. Unfinished wood exposed longer than 4 weeks, and then coated, may not
hold up properly.
• Make sure the appearance of the surfaces is clear, consistent, and “eye” appealing as stain and
sealer will accentuate inconsistencies and problem areas, not hide them.
There is much ongoing research and development of new products all the time. It is important to stay
abreast of these products. Always follow manufacturer’s recommendations when using a product.
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GOOD! LET’S GET STARTED!
You have selected the right sealer and the right application method. Assuming you have checked the
weather forecast and the moisture content of the wood, it is time to actually get started!
Remove any deck furnishings and set them well away from the work area. The BBQ can be moved
carefully around the deck, so you can work around it without taking it off the deck. Be careful when
moving a BBQ, because water can spill from inside the BBQ on to the wood.
Begin by masking off and tarp any areas that you want protected. Be careful when using plastic around
plants. It can cause a greenhouse effect and brown the leaves or kill the plants. When working over a
patio or protected area it is recommended to use two coverings - a moisture-proof tarp on the bottom and
an absorbent covering on top. This will ensure that nothing seeps through to the surface. It is further
recommended to wet down the surrounding area if possible without getting the wood surfaces wet. If a
stain drips on a wet surface, the moisture will dilute it and keep it from penetrating - making it much easier
to clean up.
If you are going to spray, protect nearby property where over-spray might cause expensive damage (such
as parked cars).
Next, sand the deck as necessary. Remove any leftover fuzzies, and perform any other preparation such
as tightening of boards, “popped” nails, etc. Fuzzies can be removed with a stiff brush, defelting pads,
kitchen scrubbies, etc. A wire brush may be used but, unless it is a brass brush, these are not
recommended. Iron filings could be left in the wood which will rust and stain later on.
Do not leave fuzzies on the deck as the job will appear unprofessional when completed. When sanding a
deck you should use sandpaper with 80-120 grit. Anything over 120 will smooth the surface and close the
pores of the wood. There may be instances to go below 80 grit but will usually need to be gone over
again with 80-120 grit range. Be very careful when sanding large areas. If certain areas are sanded in
detail and not the whole surface you may end up with a “blotchy” look in the finish job. You will have
changed the surface in some areas but not all.
Next, drag your foot across all floor nails to identify which ones are raised. Using a nail set and hammer,
drive the raised nails down. NOTE: Most raised nails are the result of unsealed wood. The wood absorbs
water and swells, pushing the nail out. When the wood dries, the nail is left in the raised position. This is
also the right time to perform any woodwork that the customer has requested (such as routing the
handrails).
At this point the surface is ready for coating. The key here is to avoid lap marks and any difference in
color or tone. You should figure out the total gallons needed and mix them in one container. This
combining and mixing of the product is called boxing. Boxing ensures a consistently uniform color on
tone. You should continue to mix product as you use it to prevent settling of product.
If you are going to spray a deck attached to a house, make it a point to carry a thinner-dampened rag with
you to clean up over-spray immediately (not in your pocket). If the house has vinyl siding and you are
using a penetrating sealer, the sealer can be absorbed into the siding in as little as a half hour of coming
into contact with it. Vinyl siding must be protected or cleaned constantly during the application of a
penetrating sealer.
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CONSISTENT SEALING PROCEDURES
Following orderly procedures and making them a habit will help you save time, save materials, and avoid
mistakes and problems. When sealing a deck, always do the outside of the railings first. Then move to the
inside of the railings. Proceed to the floor, the stairs, and finally any posts under the deck.
This will take advantage of natural overspray patterns, saving time and material.
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THE SEALING PROCESS
Always try to complete similar surfaces the same day (the same side of a house, a deck, etc.) This will
produce the best results. A project completed on different days can show different colors or tones. For
example, a sealer applied on an 80-degree sunny day will penetrate and dry differently than that of a
sealer applied on a 60-degree overcast day.
Be careful of “flash drying” on extremely hot or
humid days. Flash drying is when the product
dries on the surface and never gets “into” the
wood. Flash drying will result in a blotchy look and
areas that remain tacky and never dry. Think in
terms of surface temperatures and not air
temperatures. It may be 85 degrees air
temperature but if the wood surfaces are in direct
sunlight they could be significantly higher causing flash drying.
Another cause of flash drying is humidity. When it
is humid out the wood pores will “sweat” causing
moisture in the wood cells. If there is moisture
present an oil base product will not be able to
penetrate and fill the wood cells causing the
product to dry on the surface or “flash dry”.
When a wet-on-wet coat is recommended it
means that a second coat is applied before the
first coat dries. If the first coat dries it will take on the desired qualities and repel the second coat usually
leaving a sticky surface for days and weeks. For many oil base products this will attract dirt and debris
and become a food source for mold and mildew. The surface will usually turn dark quickly and the second
coat will most likely peel.
Some contractors refer to the second coat as back brushing. This term means to go back over the
previous coated surface with the brush
to fill in missed areas and remove
puddles and drip marks. Many
contractors will combine a first coat
spray application and back brush the
second coat.
When applying stains and sealers to
wood siding you should work from the
bottom up. By working from the bottom
up any drip will be able to be evened
out without showing any marks. If you
work from the top down any drips are
actually the first coat and any coating
over top will continue to show the drip
marks. A professional will leave
minimal or no drip marks when the job
is completed.
When solid stains are used there is
still a recommended two-coat application. The first coat should be a primer coat followed by a finish coat.
Many times two finish coats are needed. If possible, in a tint base system, have the primer tinted to the
desired color.
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While it is important to cover and seal the surfaces be aware that over-applying will often leave sticky
surfaces and problems. At the end of every job, calculate your coverage rate for that job to determine
whether you have either over-applied or under-applied.
Once the surfaces are coated they will need to dry. You should allow 24 hours for drying time. At times
the surface may appear dry however it may not be completely dry and able to withstand traffic. It is also
important to allow for proper drying time. A rain on a freshly coated deck or surface could mean disaster.
It could leave spots and need to be re-stripped.
If you are working with tarps under a raised deck or where stains or sealers may drip you may want to
leave those tarps in place until the following day.
You should now ask the customer to do a walk around inspection with you. Its time to ask for your
payment.
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“COMBO” DECKS WITH AN ACRYLIC SOLID-COLOR
Have you seen decks with stained floors and painted railings? This is called a “combo” deck, and the work
involved is difficult and expensive. This is a “hot” look these days and commands much higher prices than a
standard deck job. If the railings actually were painted, they would crack and peel and look bad within a short
time. Solid color deck stains are an excellent alternative to latex paint. They are not the best choice for deck
floors, however, since they are a sealer that, over time, will show wear patterns. Combo decks have floors
that are sealed with an oil finish and railings sealed with a solid color stain.
Never use a latex paint on deck floors either because,
after several months, the resulting wear patterns and
cracking and peeling will make the deck look awful.
If you are doing a “combo” deck, seal the floor with the
oil sealer before starting the railings. Any drips of solid
color that fall on to a recently sealed floor will be much
easier to clean up.
Begin by mixing an emulsifier with your solid-color
stain. This minimizes “soak-in” and allows you to skip
priming the wood.
Once the stain is thoroughly mixed with the emulsifier,
you can begin the application. This product can be
sprayed with an airless sprayer, similar to the acrylic sealers.
FINAL WORDS
It is wise to limit the colors you offer to your customers to two or three. Any color can be custom-ordered for a
customer, but if you try to limit the choices to a couple of colors you will be able to make 95% of your
customers happy with a minimum of inventory on hand.
If the sealer you have applied is a coating, you cannot return the furnishings back to their original location.
These sealers require 24 hours of drying time. Once the cleanup is done, take the final “after” photo for your
collection.
Variations in color in the finish job, even within a single board, are normal. The wood naturally varies in
density and absorption, which gives a naturally varied final appearance.
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TIME WASTERS / TIME SAVERS
Carry everything you might use on the job every day. If you don’t, you will surely need the one thing you
didn’t bring.
Never make a trip to or from your vehicle without carrying something.
Prepare for clean-up from the first moment on the job.
Pre-purchase 5/4 treated deck boards and dry them at your shop for several weeks. Be sure to avoid
buying “factory-sealed” wood (since these are basically wax treatments that must be stripped before the
board can be sealed). These 5/4 boards can be used for replacing floor boards on decks. Pre-buying
them means that they will have time to dry before you install them.
Establish barriers to minimize clean-up – tarps, mineral spirits, water, backdrops, etc. You can spray
mineral spirits on concrete and house siding to prevent sealer from soaking in. Remember these surfaces
must be kept wet to be effective as barriers.
Call ahead to assure that water and power are on, the gate is unlocked, and the dog is leashed.
Test your tools before setting out in the morning. Bring back-up tools with you. Sometimes your sprayer
won’t work, so having a pump-up sprayer can be a lifesaver.
A fan left on overnight will dry a damp deck and prevent dew from settling on it in the morning.
A tarp laid on a deck for 20 minutes will cool it down before sealing the floor.
An old hair dryer (or heat gun) will dry small spots of water spilled on a deck before you seal it.
Clean up tools and the job before material dries.
Wash in the morning, seal in the afternoon. The wood is always drier in the afternoon.
Establish productivity standards. If a 12x16 deck with a full set of stairs is the “standard” deck, plan to
seal a deck like this in 90 - 120 minutes with two people, or take about 2.5 – 3 hours by yourself.
Use a stainless steel razor knife to remove dried sealer from windows. Stainless steel is less likely to
scratch the window.
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MAINTENANCE
Maintaining decks after you have renewed them can be a big part of your ongoing revenue stream.
If you use a penetrating sealer, you might not have to strip (or open the surface) before re-treating. All you
really need to do is clean the deck with a perbarbonate cleaner and apply a single new coat. Usually this
new coat of sealer is a very thin one, and can easily be applied with a flat stain pad.
To prevent getting the color of the deck turning too dark, you might consider mixing the current color 1:1 with
a clear color of the same product. This will keep the color close to the original look.
The same process can be done with acrylic sealers, too. A simple wash followed by a thin application of the
same product will keep the deck looking “brand new” at a very low cost to you (and a terrific price to your
customer!).
This work requires the same procedure as any deck cleaning and sealing. Drying time is minimal, however,
since the water used in washing will not be absorbed into the wood very far (if at all).
Coatings should be “broken” before applying a maintenance coat.
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SEALING RECAP
As with cleaning, there is a right way to do this project. Once the surface to be sealed has been properly
cleaned and brightened, it is time to proceed with the finishing touches.
Once the deck has dried (at least 48 hours without rainfall during the summer) and the moisture level
meets our specifications, we can seal it and turn it into a showcase. Sealing a deck today is a pretty
straightforward procedure, so let’s get started.
1) Plan to arrive on the job no earlier than about 10:00 AM. This eliminates any problem caused by
morning dew. Call ahead (even the night before) to inform the customer of your plans. Leave
message if necessary.
2) If you are part of a two-person crew, one knocks on the door to notify occupants and the other
starts unloading and carrying tools and material to the work area.
3) Check your work order. If any sanding or nailing or routing is called for, now is the time to do it.
4) Once in the yard, find your golf tee or flag. Taking a picture now is optional.
5) Wet the patio underneath and tarp it. Pre-wet and cover all of the plants and lawn around the
deck with lightweight paper tarps. Do not get water on the deck!
6) Mix all the sealer you plan to use into one bucket; this assures color consistency.
7) Start applying nearest to the house and farthest from the stairway, putting on a light coat.
Continue down the stairway. Wait 30 minutes and repeat.
8) If any puddling occurs, back-brushing with a flat paint pad works well.
9) Some sealers require sufficient drying time before water can touch the sealer.
10) Clean the tools immediately when you are done using them.
11) Uncover plants, patio, and rinse again; return furniture to the deck (if dry).
12) Clean your equipment.
13) Now is the time to take the “after” picture. Find the golf tee or flag and take the picture and save it
for your portfolio.
14) If the time of day is significantly different than the time of the “before” picture, or the deck is too
wet to put the furniture back on, you might decide to come back another day. (Decks look more
inviting with furniture on them)
15) Once the vehicle is loaded, you should invite the homeowner to look at the job – and write you a
check. You should have completed a final walk-around to make sure a) everything was done; b)
the house was cleaned off; and c) nothing is left behind.
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SEALING EQUIPMENT
Over and above the choice of application tools, consider having the following available on the job:
1)
Extension Cord (100ft)
2)
Splatter shield
3)
Tarps (5-10) Plastic, canvas and/or paper with a 4-mil poly backing for vegetation areas
4)
Paint guards, paper shop rags, & stiff brush (for fuzzies)
5)
Empty plastic buckets
6)
Paint brushes (white china bristle)
7)
8’ step ladder, 250# rating & 24’ extension ladder, 250# rating
8)
Thinner, (in clean thinner can)
9)
Thinner, (in bucket for rinsing)
10)
Flat paint pads, extension pole
11)
Safety gear, goggles, respirator, gloves, hat, face shield, etc.
12)
Sodium hydroxide stripper (diluted for cleaning tools and spills)
13)
Broom or blower
14)
Sealer
15)
Digital Camera (or 35mm)
(1 gal & 5 gal)
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TROUBLESHOOTING
As more inexperienced homeowners and weekend warriors decide to do deck sealing, the tougher the
problems we face will become. I remember when every deck I was asked to service had never been
sealed before. Those decks were all gray and cracking and just total eyesores. It was easy for me to ride
in on my white horse and save the day.
Now the large home fix-it stores are selling every kind of DIY washing and sealing chemical known. It’s no
wonder that half the sealed decks look terrible in as little as 6 months.
This in itself is not a problem. It means we get more work. After the homeowner has done his deck once,
believe me, he seldom does it again.
The problem comes when we get a call to save a deck that’s been ruined and we discover that the
homeowner has used some horrible varnish-like sealer or some latex sealer that the home store sold him.
Don’t blame the homeowner. He was told it would go on easy, look beautiful and last forever.
This is where troubleshooting really gets interesting. There are finishes being sold every day that will
drive you out of business if you try to remove them. You may even find yourself using a super-stripper at
full-strength just to break the surface of some finishes.
We recommend that you walk away from jobs that don’t pass your test patch. When you do perform test
patches, be sure to look for multiple finishes. Sometimes the top layer strips off, but layers of other
products will not. Once you take a job, even if it is a bad one, you will have a hard time getting out of
finishing the job unless you are willing to damage your own reputation.
If you find yourself facing one of “those” jobs, you may end up using one of the new paste strippers along
with hot water and a scraper to remove these products. Always carry a spritzer with caustic stripper in it to
test surfaces (in case you don’t know what sealer has been used). If the surface doesn’t melt right away
with that test, why not let some other contractor deal with the problem?
Following is a list of other areas we can spend some time discussing:
 Poorly washed decks, fences.
 Customer-washed decks
 Uneven or poorly-applied previous sealers
 Non-wood (Trex, etc.)
 Cracked, splintered, warped wood
 Painted wood
Knots in the wood can act like straws, drawing the sealer away from the surface and out the other side. If
you use a sealer that fully penetrates, knot areas may appear to have less sealer on them because the
sealer traveled through the knot away from the surface. This sort of problem can be prevented by
brushing or spritzing mineral spirits on the knots before sealing with an oil sealer. This effort suspends the
sealer closer to the surface, which will keep the color more uniform with the rest of the wood.
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CONCLUSION
This concludes our study of sealing wood exposed to the elements.
There is no substitute for years of field experience, but we have covered every topic in this class that you
need to know to be recognized as a professional wood sealing specialist. Please retain this manual as a
Reference Guide.
The others taking this class are an important resource for you. Network with these other professionals to
maximize the benefit of taking this class. Your instructor also has an interest in your success, so stay in
contact with him as well.
We wish you success in your business. Business owners are a special breed. They carve their living out
of their own ingenuity and hard work. We salute all of you.
To complete your knowledge about cleaning and sealing decks, you should enroll in our deck cleaning
class while all of this information is fresh in your mind. Once that class is completed, you will be fully
prepared for your chosen profession.
Certification is available to you at any time. The material included in the Certification test is fully covered
in the two Wood courses and in the Manuals associated with these courses. This independent
Certification sets you apart from your competitors in a way no manufacturer-sponsored certification can.
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ADDITIONAL REFERENCE MATERIALS
The following are reprints of two USDA Forest Products Laboratory publications dealing with sealing wood.
In minor ways the information contained in this report could vary from what has been discussed so far. What
we teach is our “real-world” experience and what is found in these reports is the science and technology of
what we do.
Selection and Application
Of Exterior Stains for Wood
R. Sam Williams, Supervisory Research Chemist
William C. Feist, Supervisory Research Chemist (retired)
Forest Products Laboratory, Madison, Wisconsin
Introduction
Many homeowners prefer a wood finish that preserves the natural color of wood, such as the penetrating
finishes, as opposed to the nonpenetrating film-forming finishes. Examples of these film-forming finishes
are paints and other opaque finishes and latex semitransparent stains. For interior wood, clear filmforming finishes, such as polyurethane and spar varnish, provide a natural look. Wood finished with such
products is also easy to keep clean. For exterior wood, however, clear film-forming finishes do not last
long because of exposure to direct sunlight. Even if the sealer is resistant to sunlight, the clear film
permits the sunlight to degrade the wood at the sealer–wood interface causing loss of sealer adhesion.
Under such conditions, clear finishes crack and peel from the wood surface after 1 or 2 years, and the
wood requires extensive surface preparation before it can be refinished. Penetrating finishes provide a
way to protect the surface of exterior wood while allowing the characteristics of the wood to show through
the finish.
Penetrating finishes, which include stains, water repellents, and water-repellent preservatives, can be
used outdoors. They do not require extensive preparation of the wood surface because they do not crack
and peel from the surface. Penetrating finishes can be clear or pigmented. Clear penetrating finishes can
both protect the wood surface from weathering and allow the wood’s characteristics to show through the
finish. However, such unpigmented finishes have a shorter surface life than do pigmented finishes.
Nonpenetrating finishes, such as latex semitransparent stains and latex and oil-based opaque stains, are
often useful for situations where penetrating stains are inappropriate.
This publication describes the properties and use of stains on wood exposed outdoors. The discussion
includes background information on wood properties and treatment of wood with preservatives. Both oilbased and latex formulations of semitransparent and opaque (solid-color) stains are described.
Wood Properties
Factors affecting stain performance are growth ring orientation; the amount of heartwood, sapwood, and
juvenile wood; the durability of the wood; weathering; and moisture.
Growth Rings
Growth rings are most easily seen in a cross-sectional view of a log (Fig. 1). The portion of the growth
ring formed during the spring (earlywood or springwood) is less dense than the portion formed during the
summer (latewood or summerwood). The most drastic density change occurs at the junction of the
latewood of one growing season and the earlywood of the next. The width of the growth layer, the
thickness of individual cell walls, and the properties of these cells depend on the species, the weather
during the growing season, the site where the tree is growing, and the age of the tree.
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Heartwood and Sapwood
In addition to growth rings, another feature seen in the cross section of a log is the apparent difference in
color of the central heartwood portion compared with the outer sapwood portion (Fig. 1). Although both
heartwood and sapwood provide structural support, they serve different functions with regard to the life
processes of the tree. Water and nutrient transport, the life support system of the tree, takes place within
the inner bark and sapwood. The heartwood is not involved in moisture transport. It
serves only as structural support and a storage area for many of the organic chemicals produced by the
living tree. The species-specific chemicals stored in the heartwood are called extractives. In addition to
the anatomical differences in wood, these chemicals give each wood species its other characteristic
properties, such as color and natural decay resistance.
Although a few species, such as redwood and western red cedar, have a reputation for natural decay
resistance, only the heartwood of these species provides durability because of the high concentration of
certain extractives.
Juvenile Wood
The wood formed during the first few years of a tree’s
growth (8–10 years for most species) is called juvenile
wood. This wood has abnormal properties that may
cause large dimensional changes (generally in the
longitudinal direction). These dimensional changes can
cause severe warping of lumber. While mature wood
changes only slightly in longitudinal dimension
between its green and dry state (0.05% change),
juvenile wood can change 3% to 5%. With dimensional
change of this magnitude, fasteners may pull out and
the wood may split, bow, twist, cup, or crook.
The pith or center of the tree can most easily be seen
on the end grain of a log (Fig. 1). If a particular board
contains the pith, it is certain to contain juvenile wood.
Wood that contains juvenile wood can warp
considerably as it dries because of uneven longitudinal
dimensional changes. Warp can be minimized by
selecting lumber without the pith.
Durability
Some woods have natural durability (resistance to decay or rot). Others can be made durable through
treatment with preservatives. Durable species such as redwood and cedar are commonly used for wood
exposed outdoors, such as siding, shakes and shingles, decks, furniture, and fences. Durability is
imparted by natural chemicals, which are contained in extractives in the heartwood of these species.
Since only the heartwood contains extractives, lumber that contains a high proportion of sapwood does
not have the natural durability of lumber that contains a high proportion of heartwood.
Non-durable wood species may be factory-treated with preservative for long-term durability for use in
ground contact.
These treatments are done in large cylinders, and the preservative chemicals are forced deep into the
wood using high pressure. Preservative treatments of wood are done under carefully controlled factory
conditions, and the wood usually has a manufacturer’s guarantee. Lumber treated with preservatives may
also have a quality stamp by an independent inspection agency.
Moisture Effects
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Water is one of wood’s worst enemies. Whether in the form of vapor or liquid, water can cause shrinking
and swelling, which can lead to dimensional changes of the wood and degradation of the finish. Water
causes decay or rot of the wood and early failure of the finish, and it accelerates the weathering of wood
exposed outdoors.
Shrinking and Swelling
In general, wood shrinks as it loses moisture and swells as it gains moisture. More precisely, wood
changes dimension only between an absolutely dry state (completely free of moisture) and its fiber
saturation point (the point at which the wood fibers are completely saturated with moisture). For most
species, this fiber saturation point typically occurs at about 30% moisture content. At this point, all the
water in the wood is bound within the cell wall. At moisture content changes above fiber saturation, the
cell cavities take on or lose unbound water but the wood cell walls do not change dimensionally. Below
the fiber saturation point, however, the wood changes dimension with changing moisture content. The
magnitude of this change is dependent on species and is always different for the three axes (radial,
tangential, and longitudinal). A large percentage of wood finish degradation (for example, paint defects,
peeling, and cracking) results from moisture changes in the wood and subsequent dimensional instability.
Water Vapor and Water Effects
Shrinking and swelling of wood occur whether the water is in the form of vapor or liquid. For example,
wood swells during periods of high humidity and shrinks during periods of low humidity; it also swells and
shrinks as it gets wet from liquid water and then dries. If wood is exposed to water vapor, which occurs
indoors, the moisture content can reach only the fiber saturation point. This requires exposure to 100%
relative humidity for an extended period. Since wood is seldom exposed to this level of relative humidity
for long periods, it seldom reaches fiber saturation because of high humidity. However, if the wood gets
wet from liquid water, it can quickly reach or even go beyond fiber saturation. Problems with poor
performance of wood occur when the moisture content of wood reaches or goes beyond fiber saturation,
which is almost always caused by liquid water.
Categories of Wood Finishes
True penetrating wood finishes fall into two general categories: (a) water repellents (WRs) and waterrepellent preservatives (WRPs) (Williams and Feist 1999) and (b) solventborne oil-based semitransparent
stains. The advantage of a penetrating finish compared with a finish that forms a film is that the
penetrating finish allows the wood to breathe and the finish does not peel. Water repellents, WRPs, and
some stains are formulated so that the solvent carries the binder, preservative (mildewcide), and WR into
the wood. Another category of wood finishes is the nonpenetrating stain finishes, which do not penetrate
the wood but can be used like paint.
Water Repellents and Water-Repellent Preservatives
Water repellents and WRPs are relatively simple wood treatments that slow the uptake of water and help
keep wood dry. The only difference between these finishes is that WRPs include a fungicide or
mildewcide. Otherwise, the composition of WRs and WRPs is similar: both contain 10% to 20% binder
such as varnish resin or drying oil (linseed or tung oil), a solvent, and a substance that repels water (wax
or wax-like chemical). The oil or varnish resin penetrates the wood surface and cures to partially seal the
wood surface. The oil or varnish also helps to bind the fungicide–mildewcide and WR to the wood
surface. Solvents include organic liquids such as turpentine, naphtha, and mineral spirits or water. The
amount of WR varies among brands. Some WRs and WRPs are formulated with a low concentration of
WR so that they can be used as a pretreatment for other finishes (about 1% by volume). Others are
formulated with a high concentration of WR (about 3% by volume) and are meant to be used as standalone finishes.
Water repellents and WRPs are effective when used on wood exposed outdoors above ground. In areas
where decay is a serious problem or where wood will be in contact with the ground (wood foundations or
fence posts, for example), wood will need far more protection than that afforded by surface treatment with
a WR or WRP. In such cases, wood properly protected by treatment with a commercial preservative is
recommended. Such pressure-treated wood is normally available at lumber yards and should conform to
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recognized standards for maximum service life.
Penetrating Stains
If pigments are added to WRP solutions or to similar transparent wood finishes, the mixture is classified
as a semitransparent stain. The pigment provides color and greatly increases the durability of the finish
by protecting the wood surface from sunlight. Since semitransparent stains penetrate the wood without
forming a continuous layer, they do not blister or peel even if excessive moisture enters the wood.
Semitransparent stains permit much of the wood grain to show through; no film is formed unless too
many coats are used.
The durability of a stain system is a function of the
formulation (amount and type of pigment, resin,
preservative, and WR), the surface characteristics of
the wood species, the quantity of material applied to
the wood surface, and the amount of sunlight to which
the finished surface is exposed.
Changes in Stain Formulations
In the 1950s, the USDA Forest Service, Forest
Products Laboratory (FPL) developed a natural finish
aimed at overcoming the susceptibility of oil-based
film-forming finishes to failure through cracking and
peeling (Black and others 1979). Research showed
that the first application of the FPL natural finish to
smoothly planed surfaces that had been fully exposed
lasted 2 to 3 years. When the wood was refinished
after weathering, the finish lasted much longer. Two
coats of the finish on roughsawn or weathered
surfaces could last 10 or more years. Semitransparent
stains similar to the original FPL natural finish are now
being marketed nationwide by hundreds of
manufacturers. These formulations are usually based
on linseed oil or a modified oil. The oil penetrates the
wood extremely well when the finish is formulated with
a solvent such as mineral spirits or turpentine (Fig. 2).
Until about 1980, all penetrating stains were oil-based
solventborne formulations. These formulations readily
penetrate the wood surface and do not form a sealer (Fig. 3); therefore, they do not blister and peel, even
in excessive moisture conditions. Because stains do not form a sealer, the wood does not need to be
scraped before refinishing. Thus, the stain is easily maintained on a variety of wood surfaces.
About 1980, manufacturers started to change semitransparent stain formulations because of concerns
about solvent evaporating from these finishes. Many solvents react with pollutants in the atmosphere to
form ozone, a component of smog. These solvents are collectively known as volatile organic compounds
(VOCs). More stringent regulations that will affect paint and stain formulations are currently being
developed under the provisions of the New Clean Air Act (1991). Formulations of finishes will continue to
change to meet these regulations.
Changes in stain formulations include decreasing the amount of solvent, resulting in a formulation with a
high solids content (high-solids formulations), substituting solvents that do not cause smog, and using
waterborne formulations. The penetrating characteristics of low-VOC formulations vary considerably.
Many of these reformulated finishes penetrate the wood similar to traditional solventborne formulations,
but others tend to form a film.
For high-solids formulations that contain large amounts of natural or synthetic oils, the proper absorption
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of the finish can be hampered by the sheer volume of oil on the surface of the wood. If the oil is a drying
oil, it may dry before absorbing into dense areas, such as wide latewood bands on flatsawn lumber. The
resulting film will appear as shiny areas on the surface. High-solids formulations are still being intensely
developed, and improvement in the performance of these products is likely.
There are currently efforts by many stain companies to develop waterborne stains that penetrate wood.
These waterborne formulations have been only moderately successful at duplicating the properties of
traditional oil-based solventborne stains.
Preparation of Stains
Although directions for making semitransparent stains were published by Black and others (1979), this
formulation was possible only because of the availability of pentachlorophenol (penta). This pesticide is
no longer available to the consumer. In addition, the mildewcides listed by Black and others (1979) are
only available in formulated finishes. Therefore, it is not possible for the consumer to formulate a mildewresistant semitransparent stain. A wide variety of commercial finishes are available and many of these
contain effective mildewcides.
Nonpenetrating Stains
As originally formulated, a stain was synonymous with a penetrating finish. Now, a number of
nonpenetrating finishes are marketed as stains. These finishes include latex semitransparent stains and
latex and oil-based opaque (solidcolor) stains. Because these stains do not penetrate wood as do the
solventborne oil-based semitransparent stains, they must be used and applied like paint and other filmforming finishes.
Latex Semitransparent Stains
The appearance of latex semitransparent stains is similar to that of oil-based semitransparent stains, but
the latex polymer does not penetrate the wood as does oil. The semitransparent look is achieved by the
formation of a thin film. This film is not thick enough to provide durability, and it tends to degrade by
flaking from the wood surface.
Latex Opaque Stains
Latex opaque or full-bodied (solid-color) stains are similar to latex semitransparent stains but contain a
higher amount of solids (that is, they form a thicker film when applied to the same area per amount of
stain). Latex opaque stains do not have the hiding power of a true paint. By the same token, a second
application of stain will not hide the original stain. For example, if an opaque stain is applied over wood
that is partially unstained and partially stained or painted, these differences may show through the new
sealer. A second coat of opaque stain will usually eliminate this difference. Latex stains can also show lap
marks (but not to the same extent as do solventborne oil-based semitransparent stains) and extractive
bleed (particularly with lighter colors). Latex opaque stains have good color retention, are flexible, and are
less prone to mildew than are oil-based stains.
Oil-Based Opaque Stains
Oil-based opaque (solid-color) stains are less flexible than latex stains and more prone to crack and flake,
particularly if applied as a single coat over flat-grained wood. These stains provide good service life if
applied in multiple coats, which build up the film, but they will not give the same appearance as a
penetrating stain.
Preservatives
The preservatives used in stains deserve special mention. They should not be confused with the
preservatives used for pressure treating wood, such as chromated copper arsenate (CCA). The chemical
treatments described here are contained in the finish and are formulated for brush application. They are
not available except as formulated in a finish. These chemical treatments can be formulated in WRs,
WRPs, or semitransparent stains. Some commonly available preservatives are described in the following
list. Some European commercial formulations available in the United States may contain preservatives
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other than those listed here.
-Iodo-2-propynyl butyl carbamate (commonly called Polyphase) is currently used in several
commercial WRP formulations and pigmented stains. It is available in both solvent- and waterborne
systems at approximately 0.5% composition by weight..
2-(thiocyanomethylthio) benzothiazole (TCMTB) is used alone or in combination with methylene bis
(thiocyanate) (MTC or MTB). This preservative can also be effective as a fungicide for WRP and stain
formulations. It is available in both solvent- and waterborne systems at ~0.5% concentration by weight.
w stains, in
both solvent- and waterborne formulations. Approximately 2% concentration by weight of zinc metal is
recommended.
-8-quinolinolate is available in commercial WRPs and may be available in stains. This
preservative imparts a green–brown color to the wood. Effective concentrations range from 0.25% to
0.675%.
-trichloromethylthio phthalimide (the latter also commonly
called Folpet) is in a number of commercial stain formulations at 0.5% to 1.0% composition by weight.
longer readily available to the consumer in the ready-to-use (5% penta) or the concentrated (40% penta)
formulation because of its high toxicity and status as a carcinogen. The use of pentachlorophenol is
controlled and restricted to registered pesticide applicators.
Two FPL publications on wood finishes regarding the purchase and use of pentachlorophenol are
outdated (Black and others 1979, Feist and Mraz 1978). This preservative has been classified by the
Environmental Protection Agency as a restricted-use pesticide and is no longer readily available as a
preservative for the formulas described in these publications unless the user is licensed to apply
pesticides. In addition, pentachlorophenol has been removed from all commercial stain and WRP
formulations. All concentrations of pentachlorophenol have been restricted for sale, including the 40%
concentrate described in the FPL publications cited here.
Many wood preservatives are being used as substitutes for pentachlorophenol in commercial stain and
WRP formulations. However, most of these may be difficult to obtain for mixing into a formulation. These
products need to be purchased directly from the manufacturer or from a chemical supply house. Some
may be sold only to commercial operators. Registrations of preservatives are under constant review by
the Environmental Protection Agency and the U.S. Department of Agriculture. Only preservatives that
bear a Federal registration number and carry directions for home and garden use should be used.
Because the registration of preservatives is under constant review by State and Federal authorities, a
responsible State agency should be consulted as to the current status of the preservative.
Manufacturers’ safety and Data Sheets (MSDSs) should be available from paint dealers for WRP
solutions and semitransparent stains. These MSDSs should contain information on mildewcides or
fungicides contained in these formulations.
Application of Stains
Stains can be applied by brush, pad, roller, or spray equipment. Brushing improves penetration and
uniformity of appearance. Be sure to follow the manufacturerr’s directions for temperature limitations
because stains do not cure properly if the temperature is too low. When staining a house, following the
sun around the house and working only in the shade will help to decrease the tendency for lap marks to
form. Working on the entire wall while it is in the shade will also prevent uneven penetration caused by
variation in surface temperature. The stain may not absorb properly under the eaves or on the north side
of buildings (northern hemisphere) where the finish is protected from the weather. Take care to feather
the new stain into the old stain under eaves. The north side of the house probably will not need to be
stained as often as the other sides.
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Oil-Based Semitransparent Stains
The most important difference between solventborne oilbased semitransparent stains and other stains
and paints is the ability of the oil-based semitransparent stains to penetrate wood. These stains can be
used on new or weathered wood without extensive surface preparation. They can also be used on wood
previously finished with other penetrating finishes (WRs and WRPs) after the finished wood has
weathered. They cannot be used on wood that was previously finished with a film-forming finish unless
that finish is completely removed.
Solventborne oil-based semitransparent stains are the finish of choice for wood that is fully exposed to
the weather (Fig. 4). The finish repels liquid water but allows the wood to breathe (that is, it allows the
wood to dry faster after wet or humid weather). Since the stain does not form a film, it cannot peel. It can
be used on both smooth and roughsawn wood, but it performs much better on roughsawn wood.
New Wood
On smoothly planed wood surfaces, a single
application of semitransparent stain at the rate of 400
to 500 ft2/gallon (10 to 12 m2/L) is recommended. A
second coat may not penetrate uniformly on smooth
surfaces, resulting in glossy and flat areas (Fig. 5).
The first coat on a smooth surface may last only 2 to 3
years. However, if the wood is refinished after
weathering, the finish may last 8 to 10 years.
When finishing smooth surfaces of high-density
species like Douglas Fir and Southern Pine, the
surface may be treated with a WRP and allowed to
weather for a year before staining. The first coat of
stain will then penetrate uniformly and be more
durable because weathering makes the surface more
absorptive. On surfaces that have been made
absorptive by weathering or rough sawing, a gallon of
finish should cover 150 to 200 ft2 (3.5 to 4.5 m2/L). An
effective method is to use wet coats, applying the
second coat not more than 1 hr. after the first. Both
coats can then penetrate. If excess stain remains on
the surface after an hour, a second coat should not be
used. To prevent formation of glossy spots, excess
stain remaining on the surface 1 h after application
can be removed using rags or brushed to more
absorptive adjacent areas. See section on Safety
Concerns for caution on handling stain-covered
materials like oil-soaked rags. Such materials are a
fire hazard.
Refinishing
When refinishing semitransparent stains, the finish
should penetrate well into the previously finished
surface. If the stain penetrates properly, it will appear
flat. If the stain does not penetrate well, it will dry slowly with many glossy areas and probably will not be
as durable as it is on new wood. Old varnish and paint films should be completely removed before
applying stain. Again, stain that has not penetrated after 1 h should be removed from the surface. For
refinishing wood after a previous application of stain has worn away, the stain may penetrate better if
stain). Follow the manufacturer’s directions.
Specific Considerations
Some oil-based semitransparent stains dry rather slowly; a day of good drying weather is generally
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required for thorough drying. Lap marks can occur with stains because of their semitransparent nature
(Fig. 6). Lap marks are caused by applying the stain over a dry or partially dry area adjacent to the area
being finished, resulting in two coats at the juncture of the two areas. To avoid lap marks, the finish
should be applied by brushing with the grain of the wood for the full length of the board or course of siding
without stopping. The stain should also be stirred frequently during application to maintain uniform
suspension of the pigment.
Pollution Prevention
As mentioned previously, many organic solvents
interact with other pollutants to form ozone. This is a
serious problem in many metropolitan areas. Ozone
concentrations peak during the late afternoon of warm
and sunny summer days; sunlight catalyzes the
reaction. When using finishes that contain these
solvents, pollution can be minimized by using the
following guidelines:

ainting on days with an ozone alert.

afternoon so that the solvents can dissipate before the
next day.

Advantages
Oil-based semitransparent stains have good color retention and durability on a variety of smooth and
rough wood surfaces. They can be applied to all exterior wood. Stains formulated for outdoor use differ
from those formulated for indoor use. Stains for outdoor use contain toxic preservatives or mildewcides.
Read the label on the original container carefully to determine if the material is allowed and
recommended for indoor use. When in doubt, consult the manufacturer to determine which mildewcide
was used in the finish and whether it is appropriate for your proposed use.
Latex Semitransparent Stains
Latex semitransparent stains can be used much like solventborne oil-based semitransparent stains, but
they do not penetrate the wood surface. As with oil-based stains, more finish can be applied to
roughsawn wood, and therefore longer service life is obtained on these surfaces. As with oilbased
semitransparent stains, use care to avoid lap marks. Latex stains differ from oil-based stains in their
refinishing characteristics; they must be applied to a sound surface.
Refinishing wood that has been finished with a latex semitransparent stain requires substantial surface
preparation. If the previous finish has begun to flake or peel or if the wood surface has been degraded
through weathering, the surface must be sanded or power washed. If the wood is refinished before the
finish begins to flake, a second application of stain will increase the thickness of the film and improve its
durability. However, the thicker film will further obscure the original wood. It is better to use a full-bodied
opaque stain to provide a film.
Use of latex semitransparent stains should be limited to places relatively protected from the weather,
such as siding. It is best if the siding is protected with wide overhangs and if the building does not have
high exposed gable-ends.
Latex and Oil-Based Opaque Stains
Nonpenetrating stains can provide excellent service life to wood and wood-based products such as
hardboard. However, the wood surface must be carefully prepared if these stains are to be used on
weathered wood or over wood previously finished with semitransparent stain. The weathered surface
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must be removed prior to finishing. Remove by sanding (50–80 grit sandpaper), wet sandblasting, or
powerwashing. For best performance, the stain should be applied in multiple coats. Like latex
semitransparent stains, both latex and oil-based opaque (solid-color) stains should not be used on
structures fully exposed to the weather. Unfinished wood exposed to direct sunlight for longer than 4
weeks may not hold a film-forming finish properly. Opaque stains can be used successfully on smooth
and roughsawn siding and composites but should not be used on structures such as
decks and fences.
New Wood
As with other film-forming finishes, the coverage of the first coat of opaque stain on smooth wood should
be about 400 ft2 per gallon (10 m2/L). On roughsawn wood, the coverage should be about 250 ft 2 per
gallon (6 m2/L). Slightly more coverage should be obtained with the second coat. As with other filmforming finishes, the service life of opaque stain depends on the film thickness. Since the thickness on
rough wood is considerably greater (less coverage) than that on smooth wood, the service life can be
expected to be better. On rough wood, two coats may last 8 to 10 years. On smooth wood, two coats may
last only 4 to 5 years. A single coat on smooth wood may last only 2 to 3 years.
If latex stains are used like paint (that is, application of
multiple coats to build up a film of 4–6 mil (0.1–0.15
mm)), they provide excellent service life. If multiple coats
are used, the first coat can serve as the primer or a highquality latex primer compatible with the stain can be
used for the first coat. As with any latex paint, it is
important to follow the manufacturer’s recommendations
concerning application, particularly the temperature
restrictions. Latex sealers generally require at least
properly
coalesce
recommendations).
(consult
manufacturer’s
Since oil-based opaque stains are often formulated with
linseed oil, the first coat can absorb into the wood to
some extent, particularly if the stain is thinned slightly
with mineral spirits. Priming the wood with an oil-based
primer will also enhance the performance of the stain. An
oil-based primer can be used with either oil-based or
latex opaque stains, particularly with light colors where
extractive bleed could be a problem. A latex primer can
be used only with latex opaque stains. Priming will help
eliminate lap marks and decrease extractive bleed. This
is especially important with lighter colors of stain. Oil-
Proper Disposal of
Stain-Covered Materials
and Lead-Based Paint
Caution: Solventborne stains usually contain
drying oils. As the oils dry, they produce heat,
which is sufficient to ignite flammable items like
oily rags. This ignition can often occur quickly —
even while the rags are left unattended during a
lunch break. Dispose of stain-covered materials
properly; they are a fire hazard.
Refinishing that requires disturbing, removing, or
demolishing portions of a structure that are coated
with lead-based paint poses serious problems. The
homeowner or contractor should seek information,
advice, and perhaps professional assistance for
addressing these problems. Contact the Department
of Housing and Urban Development (HUD) for the
latest information on the removal of lead-based
paints. Debris coated with lead-based paint is
considered hazardous waste and must be disposed
of as such.
lower.
Refinishing
Wood finished with an opaque stain can be refinished in the same way as painted wood. The surface
must be sound. All loose or flaking stain must be removed, and the surface must be free of dirt. Any areas
that have peeled should be sanded and primed; the stain can be used to prime these bare spots.
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After sanding bare spots, feather the edges of the
finish surrounding the peeled area. However, many
older finishes contain lead pigments. Sanding wood
painted with these finishes without proper protective
equipment is a serious health risk. In addition, the
residue must be handled as hazardous waste. Contact
local authorities concerning regulations for removal
and disposal of lead-based paint and for more explicit
information on health and safety concerns related to
lead-based paint.
Specific Considerations
Like semitransparent stains, opaque stains can show
lap marks. To avoid lap marks, use the same
techniques used for semitransparent stains. Follow the
manufacturer’s recommendations on temperature and
length of time between coats.
Advantages
Opaque stains can be used in situations where the
appearance of a stain is desired but penetrating stains
cannot be used. For example, if a previously applied
semitransparent stain has weathered unevenly, it is
often difficult to feather the semitransparent stain from
the bare (unstained) wood to the stained wood.
Opaque stains can be used to cover both areas. As
mentioned previously, a second coat is necessary to
mask the differences between the stained and unstained areas, or the bare areas need to be primed first.
Again, be sure to sand all bare areas to assure good adhesion of the finish.
Removal of Mold and Mildew
Mildew should be removed from wood before it is
stained (Fig. 7). Pretreat mildewed wood with a
commercial cleaner or a chlorine bleach–water
solution prior to refinishing. Allow the wood to dry 1 or
2 days before refinishing.
Safety Concerns
Use care when applying stains. The solventborne
formulations are volatile, flammable mixtures. Do not
breathe their vapors or expose the solutions to flame
or sparks. It is wise to wear protective clothing on the
hands and arms and to take care that the solution is
not splashed in the eyes or on the face. Be especially
careful using WRPs because these solutions contain
mildewcides, which are toxic.
Removal of Mildew
Commercially available wood cleaners work quite
effectively to remove mildew and other stains on
wood.
A mildew cleaner can also be made by dissolving
1 part liquid household bleach and some powdered
detergent in 2 to 4 parts water.
Suggested formula:
1/3 cup household detergent
1 qt (5%) sodium hypochlorite (liquid household
bleach)
3 qt warm water
(1 cup = 0.2 L; 1 qt = 0.9 L)
Caution: Do not use a detergent that contains
ammonia; ammonia reacts with chlorine-containing
Store finishes in original containers in a locked space,
bleach to form a poisonous gas. Many liquid
out of reach of children and pets, and away from
detergents may contain other additives that react with
foodstuff. Use all finishes selectively and carefully.
bleach.
Follow recommended practices for the disposal of
surplus preservatives and preservative containers.
Immerse finish-contaminated materials in water, then
seal in plastic or an empty can until they can be disposed of properly.
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Conclusion
Wood is the material of choice for many structures. As with any building material, how wood is used
depends on its properties, such as strength and stiffness, as well as finishing characteristics and
maintenance requirements. Problems such as poor finish performance, mildew, checking and splitting,
and wood decay can be controlled with proper care and maintenance.
Such problems can be avoided or attenuated through knowledge about the factors that affect wood,
particularly wood exposed outdoors. If wood structures are given proper care initially and are maintained
periodically, they can be functional and structurally sound, as well as aesthetically pleasing, for decades.
Natural finishes such as WRPs and semitransparent oil-based stains can greatly improve the durability
and appearance of wood exposed outdoors.
References
Black, J.M.; Laughnan, D.F.; Mraz, E.A. 1979. Forest
Products Laboratory natural finish. Res. Note FPL–046
(Rev.) Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.
Feist, W.C.; Mraz, E.A. 1978. Wood finishing: Water
repellents and water-repellent preservatives. Res. Note FPL–0124 (Rev.) Madison, WI: U.S. Department
of Agriculture, Forest Service, Forest Products Laboratory.
Williams, R.S.; Feist, W.C. 1999. Water repellents and
water-repellent preservatives for wood. Gen. Tech. Rep.
FPL–GTR–109. Madison, WI: U.S. Department of
Agriculture, Forest Service, Forest Products Laboratory.
© 1999 - 2010, Contractors Foundation
65
Water Repellents and Water-Repellent
Preservatives for Wood
R. Sam Williams, Supervisory Research Chemist
William C. Feist, Supervisory Research Chemist (retired) Forest Products Laboratory, Madison, Wisconsin
Introduction
Some woods have natural durability against decay (rot). Others can be made durable through treatment
with preservatives. Durable species such as redwood and cedar are commonly used for wood exposed
outdoors, such as siding, shakes and shingles, decks, furniture, and fences (Table 1). Durability is
imparted by natural chemicals, which are contained in extractives in the heartwood of these species.
Heartwood is the center part of the wood; the outer part is sapwood (Fig. 1). Since only the heartwood
contains extractives, lumber that contains a high proportion of sapwood does not have the natural
durability of lumber that contains a high proportion of heartwood.
Non-durable wood species may be factory-treated
with preservative for long-term durability for use in
ground contact. These treatments are done in large
cylinders, and the preservative chemicals are forced
deep into the wood using high pressure.
Preservative
chemicals
include
creosote,
pentachlorophenol,
ammoniacal
copper
zinc
arsenate (ACZA), ammoniacal copper quaternary
compound (ACQ), and chromated copper arsenate
(CCA). Wood treated with CCA is one of the most
common types of preservative-treated lumber.
Several other preservatives are currently used and
still others are being developed. Preservative
treatments of wood are done under carefully
controlled factory conditions, and the wood usually
has a manufacturer’s guarantee. A number of wood
preservers certify their treatment with a tag on each
piece of lumber.
Water repellents (WRs) and water-repellent
preservatives (WRPs) are penetrating wood finishes
that increase the durability of wood by enabling the
wood to repel liquid water (Fig. 2). This ability to
repel water is imparted by a wax, an oil, or a similar
water-repelling substance. By repelling water, WRs and WRPs enable wood to resist decay and
discoloration by wood-decay fungi, which need moisture to live. The addition of a fungicide to the water
repellent, which converts the WR to a WRP, further enhances the effectiveness of the finish by inhibiting
the growth of mildew and decay fungi. Water repellents and WRPs also decrease the swelling and
shrinking that lead to cracking and warping. They protect painted wood from blistering, cracking, and
peeling. In wood species that contain colored water-soluble extractives, such as redwood and cedar,
WRs and WRPs help reduce the discoloration caused by extractive bleed.
Wood is the material of choice for many structures. As with any building material, how wood is used
depends on its properties, such as strength and stiffness, as well as its finishing characteristics and
maintenance requirements. Problems such as poor finish performance, mildew, checking and splitting,
and wood decay can be controlled with proper care and maintenance. Such problems can be avoided or
attenuated through knowledge about the factors that affect wood, particularly wood exposed outdoors. If
wood structures are given proper care initially and are maintained periodically, they can be functional and
structurally sound, as well as aesthetically pleasing, for decades.
This report includes a discussion of the effects of outdoor exposure on wood, characteristics of WR and
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66
WRP formulations, and methods for applying WRs and WRPs.
Effects of Outdoor Exposure
Properly seasoned wood that stays dry is not subject to decay, premature failure of paints and finishes,
and problems associated with weathering, such as excessive splitting and checking, raised grain,
extractive bleed, and discoloration.
Moisture Effects
Water is one of wood’s worst enemies. Whether in the form of vapor or liquid, water can cause shrinking
and swelling, which can lead to dimensional changes of the wood and degradation of the finish. Water
causes decay or rot of the wood and early failure of paint, and it accelerates the weathering of wood
exposed outdoors.
Table 1—Domestic wood species according to approximate relative decay resistance of heartwood
Resistant or very resistant
Moderately resistant
Slightly resistant or nonresistant
Baldcypress (old growth)
Catalpa
Cedar
Cherry, black
Chestnut
Cypress, Arizona
Juniper
Locust, black*
Mesquite
Mulberry, red*
Oak
Bur
Chestnut
Gambel
Oregon white
Post
White
Osage orange*
Redwood
Sassafras
Walnut, black
Yew, Pacific*
Baldcypress (young growth)
Douglas-fir
Honeylocust
Larch, western
Oak, swamp chestnut
Pine, eastern white
Southern Pine, longleaf, slash
Tamarack
Alder
Ash
Aspen
Basswood
Beech
Birch
Buckeye
Butternut
Cottonwood
Elm
Hackberry
Hemlock
Hickory
Magnolia
Maple
Oak, red, black
Pine**
Poplar
Spruce
Sweetgum
True fir, western, eastern
Willow
Yellow-poplar
* These
** Other
woods have exceptionally high decay resistance.
than longleaf, slash, and eastern white pine.
Shrinking and Swelling
In general, wood shrinks as it loses moisture and swells as it gains moisture. More precisely, wood only
changes dimension between an absolutely dry state (completely free of moisture) and its fiber saturation
point (the point at which the wood fibers are completely saturated with moisture). This fiber saturation
point typically occurs at about 30% moisture content for most species. At this point, all the water in the
wood is bound within the cell wall. At moisture content changes above fiber saturation, the cell cavities
take on or lose unbound water but the wood cell walls do not change dimensionally. Below the fiber
saturation point, however, the wood changes dimension with changing moisture content. The magnitude
of this change is dependent on species and is always different for the three axes: radial, tangential, and
longitudinal (Fig. 3). A large percentage of wood finish degradation (e.g., paint defects, peeling, and
cracking) results from moisture changes in the wood and subsequent dimensional instability.
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Water Vapor and Water Effects
Shrinking and swelling of wood occur whether the water
is in the form of vapor or liquid. For example, wood
swells during periods of high humidity and shrinks during
periods of low humidity; it also swells and shrinks as it
gets wet from liquid water and then dries. As discussed,
wood can swell until it reaches fiber saturation. If wood is
exposed to water vapor, such as occurs indoors, the
moisture content can only reach the fiber saturation
point. This requires exposure to 100% relative humidity
for an extended period. Since wood is seldom exposed
to this level of relative humidity for long periods, it
seldom reaches fiber saturation because of high
humidity. However, if the wood gets wet from liquid
water, it can quickly reach, or even go beyond, fiber
saturation. Problems with poor performance of wood
occur when the moisture content of wood reaches or
goes beyond fiber saturation — this is almost always
caused by liquid water. Throughout the remainder of this
report, the term water refers only to liquid water, the term
water vapor to humidity, and the term moisture to both
water and water vapor.
Weathering
Regardless of the care taken in building a structure,
wood ages when exposed outdoors. This aging
process is called weathering. Weathering is a
degradation of the wood’s surface caused by the
combined effects of the ultraviolet (UV) radiation in
sunlight, water, and abrasion by wind-blown sand or
other particulates. This degradation should not be
confused with decay. Weathering is first manifested by
a change in the color of the wood. The color of most
preservative-treated lumber is either light green (from
copper and chromium salts in the preservative) or
brown (from added dye). Cedar and redwood have the
freshly sawn natural color of these species. With
weathering, dark wood, such as redwood and cedar,
tends to get lighter, whereas light wood, such as pine
and fir, tends to get darker. In some climates, such as
along the seashore, wood tends to weather to a
silvery gray. This color is a combination of mildew
growth and cellulose enrichment of the surface. The
weathering process removes the colored extractives
and lignin, leaving cellulose. If protected from
excessive moisture, redwood and cedar are prone to
weather to silver–gray. Wood that has been pressuretreated with CCA but not treated with a WRP will
initially turn to dull gray. Eventually, this wood will also
become silver–gray. The change in color is followed
by a loosening of wood fibers and gradual erosion of
the wood surface (Fig. 4). Rain washes the degraded wood materials from the surface. Rain and changes
in humidity also cause dimensional changes in the wood that accelerate this erosion process. Erosion is
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more rapid in the less dense earlywood than in the latewood, which leads to an uneven surface (Fig. 4).
Surface
erosion,
however,
proceeds slowly. The erosion
rate for solid softwoods in
temperate zones is on the order
of ¼ to 1/2 in. (6 to 12 mm) per
century and depends mainly on
the intensity of UV radiation and
on the wood species (Fig. 5).
For hardwoods, the erosion rate
is 1/8 to 1/4 in. (3 to 6 mm) per
century. The erosion rate
depends on the
exposure of the wood to sun and
rain and the care the wood
receives. Control of water
absorption by the wood retards
weathering and decay.
Extractive Bleed
A
common
cause
of
discoloration is extractive bleed.
All species contain extractives,
but extractive bleed is most
prevalent on highly colored
woods. The discoloration often
occurs around fasteners (Fig. 6)
because the hole in the wood
caused by the fastener cuts
many wood cells. These cut cells increase water absorption. Water dissolves the extractives, and when
the wood dries, the extractives accumulate at the surface and sunlight causes them to polymerize.
Although extractive bleed can be a problem on wood siding, it is seldom a problem on horizontal wood
surfaces such as decks because the extractives are usually washed from the deck by rain before they
polymerize. If extractive bleed is a problem, the extractives can be removed by scrubbing the wood with
soap and water. Do not use a wire brush because the brush will contaminate the surface with iron, which
will cause iron stain. Finishing wood with a WRP greatly minimizes extractive bleed.
Iron Stain
A common form of staining on wood surfaces results from contamination with iron. A portion of the
extractives in wood includes a group of chemicals collectively called tannins. The amount of tannins
depends on species; oak, redwood, and cedar are rich in tannins. Tannins react with iron to form a blue–
black stain on wood. Iron stain and extractive bleed are compared in Figure 6. Note the darker color of
the iron stain. Common causes of iron stain include use of ungalvanized or poorly galvanized fasteners,
cleaning with steel wool or a wire brush, and contact of the wood with any iron or steel. Finishing wood
with a WR or WRP greatly minimizes iron stain.
Removal of Iron Stain
Iron stain can be removed by scrubbing the stained area with a aqueous solution of oxalic acid in water.
Oxalic acid is usually sold at drugstores and hardware stores.
Dissolve 1 to 4 oz of oxalic acid in 1 qt of hot water.
Scrub stained area using a stiff-bristle brush. Thoroughly rinse with water after treatment.
[Note: 1 qt = 0.9 liter; 1 oz = 28 g]
Caution: Oxalic acid is toxic. Wear rubber gloves and avoid contact with skin. Work in a well-ventilated
area. Avoid splashing the solution on plants because it can damage the foliage. Wash hands before
eating or using tobacco products. Store in a locked space out of reach of children.
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Raised Grain
The wetting and drying cycle of wood exposed outdoors
can raise the grain of the wood, resulting in a rough
surface. On flat-grained lumber, the raised grain may
appear as thin knifelike feathers along the earlywood–
latewood interface (Fig. 7). This degradation leads to a
splintered wood surface and eventually to checking and
cracking. Checking may increase the uptake of water,
thus accelerating the degradation process.
Decay
Whereas weathering is degradation of the wood
surface, decay (also called rot) affects the full volume of
wood. Decay is degradation caused by a variety of
decay fungi that are capable of breaking down the
structural components of wood for food. The fungi
tunnel throughout the full volume of the wood,
degrading the polymers that form the wood cells
through a complicated biochemical process. Since
these polymers give wood its strength, considerable
loss of strength occurs long before visible damage is
apparent. Wood decay fungi must have adequate
moisture to grow. Although the amount necessary for
growth varies depending on the species of fungi, in
general, the wood must be near fiber saturation for
fungal growth.
Mildew
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Mildew is caused by a type of stain fungi, which differ
from decay fungi. Mildew is not capable of degrading the
structural components of wood; therefore, it does not
cause a decrease in wood strength. Unlike decay fungi,
mildew fungi do not tunnel through the wood but live only
on the surface. Like decay fungi, mildew fungi often
flourish when excessive water is present. Moisture also
encourages the growth of lichens and other
microorganisms that discolor the wood surface (Fig. 8).
Wood can develop mildew growth rapidly, particularly if
treated with linseed oil or other natural oils, which form a
food source for the fungi. Because the conditions that
favor the growth of mildew fungi also favor the growth of
wood-degrading fungi, be suspicious if wood has mildew
or other discoloration. Mildew can affect all species of
wood, including naturally decay resistant species and
wood treated with CCA. Some extractives are food for
mildew. Thus, species with high extractives content are
slightly more susceptible to discoloration by mildew.
Mildew fungi are objectionable because they discolor the
wood. The most common discoloration is an overall
gray. Mildew can also appear as black blotchy stains
(Fig. 9). Mildew can be removed with a liquid household
bleach– water solution (Fig. 10). (Liquid household
bleach is a 5% aqueous solution of sodium hypochlorite.
See section on removal of mold and mildew.) Better yet,
periodic treatment of the wood with a WRP can prevent
mildew.
Advantages of Water-Repellent Preservatives
 Retard decay in aboveground applications
 Decrease raised grain, checking, warping, and
splitting
 Inhibit mildew growth on both painted and
unpainted wood
 Stop extractive bleed
 Retard iron stain
 Improve paint adhesion
Formulations
Water repellents and WRPs are relatively simple wood
treatments that slow the uptake of water and help keep
wood dry. The only difference between WRs and WRPs
is that WRPs include a fungicide or mildewcide.
Otherwise, the composition of WRs and WRPs is similar:
both contain 10% to 20% binder such as varnish resin or
drying oil (linseed or tung oil), a solvent, and a substance
that repels water (usually a wax). The oil or varnish resin
penetrates the wood surface and cures to partially seal
the wood surface. The oil or varnish also helps to bind
the fungicide–mildewcide and water repellent to the
wood surface. Solvents include organic liquids such as
turpentine, naphtha, and mineral spirits or water. The
amount of water repellent varies among brands. Some
WRs and WRPs are formulated with a low concentration
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of water repellent so that they can be used as a pretreatment for other finishes (about 1% by volume).
Others are formulated with a high concentration of water repellent (about 3% by volume) and are meant
to be used as stand-alone finishes.
Preservatives
The chemical preservatives used in WRPs deserve special mention. They should not be confused with
the preservatives used for pressure treating wood, such as CCA. The term preservative is used because
the WRP chemical is a registered pesticide. These preservatives are moderately effective fungicides–
mildewcides and give some decay resistance to wood in aboveground exposure. The chemical
treatments described here are contained in the finish and are formulated for brush application. They are
not available except as formulated in a finish. These formulations may contain one of the following
preservations:
 3-Iodo-2-propynyl butyl carbamate (commonly called Polyphase) is currently used in several
commercial WRP formulations and pigmented stains. It is available in both solvent- and
waterborne systems at ~0.5% composition by weight.
 2-(thiocyanomethylthio) benzothiazole (TCMTB) is used alone or in combination with methylene
bis (thiocyanate) (MTC or MTB). This preservative can also be effective as a fungicide for WRP
and stain formulations. It is available in both solvent- and waterborne systems at ~0.5%
composition by weight.

stains, in both solvent- and waterborne formulations. Approximately 2% concentration by weight
of zinc metal is recommended.
 Copper naphthenate is available commercially in WRPs. Solutions and treated wood are bright
green; treated wood weathers to pale green–brown in full sunlight. This preservative is available
in solvent- and waterborne formulations at ~2% concentration by weight of copper metal. It is one
of the few fungicides used to pressure-treat wood for belowground decay resistance. It is very
effective for use on cut ends of posts before being placed in the ground.
 Copper-8-quinolinolate is available in commercial WRPs and may be available in stains. This
preservative imparts a green–brown color to the wood. Effective concentrations range from
0.25% to 0.675%.

-trichloromethylthio phthalimide (the latter also
commonly called Folpet) is in a number of commercial stain formulations at 0.5% to 1.0%
composition by weight.
 Pentachlorophenol (penta) was used quite extensively in WRP formulations until about 1980. It is
no longer readily available to the consumer in the ready-to-use (5% penta) or the concentrated
(40% penta) formulation because of its high toxicity and status as a carcinogen. The use of
pentachlorophenol is controlled and restricted to registered pesticide applicators.
Some European commercial formulations available in the United States may contain preservatives other
than those listed here. Treatments containing borates are also being marketed as preservatives for wood
products.
Terminology
The word preservative is a general term that includes many different chemicals used on wood to make it
less susceptible to attack from a variety of organisms. These organisms include insects, marine borers,
and various types of fungi such as stain and decay. Some of these chemicals are effective against a
range of organisms. Others are very specific and protect wood from only one type of organism. No single
chemical will protect wood from all degrading organisms. Terms often used interchangeably with
preservative include pesticide, fungicide, insecticide, and mildewcide. These chemicals are all
preservatives, but they protect wood from specific organisms. Fungicides protect wood from wooddegrading fungi. Many fungicides will also protect wood against mildew. In turn, mildewcides can
sometimes provide protection against decay fungi, but they are most effective against mildew and similar
staining fungi. The chemicals used to formulate WRPs are generally fungicides and impart resistance to
both mildew and decay fungi.
Changes in Formulations
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Penetrating finishes were traditionally formulated
using organic solvents as carriers for the binder
and water repellent. The organic solvents
facilitated the absorption of these components,
thus giving a penetrating finish. The formulations
were relatively simple solutions of binder, wax,
and fungicide. About 1980, WRP formulations
started to change because of concerns about
solvent evaporation from these finishes in urban
areas with smog. A number of waterborne
formulations were introduced. In addition,
several manufacturers began marketing low
volatile organic compound (VOC) formulations
for use in some areas. (VOC is a general term
for volatile solvents and co-solvents used in both
solvent- and waterborne finishes.)
Under provisions of the New Clean Air Act (1991), more stringent regulations that affect paint
formulations were developed. On September 11, 1998, the Environmental Protection Agency published a
rule in the Federal Register for the limitations of solvents used in architectural sealers. The regulation
takes effect in September 1999 for sealers that do not contain preservatives. For those sealers containing
preservatives, the rule takes effect in September 2000. This legislation will have the greatest effect on the
formulation of penetrating finishes such as WRs, WRPs, and semitransparent stains. Other formulations
will also continue to change to meet these regulations. The restriction of solvents has caused
manufacturers to reformulate penetrating finishes by either removing solvents to give high solid finishes
or by relying on waterborne systems.
Penetrating Characteristics of Water-Repellent Preservative Formulations
There is considerable variation in the penetrating characteristics of waterborne formulations. Many
waterborne formulations absorb into the wood in the same way as solvent-borne formulations, but others
tend to form thin surface films. The manufacturer’s product literature may indicate the absorption
characteristics of the finish.
In high solid formulations containing large amounts of natural or synthetic oils, the proper absorption of
the finish can be hampered by the sheer volume of oil on the surface. If the oil is a drying oil, it may dry
before absorbing into dense areas, such as wide latewood bands on flat-sawn lumber. The resulting film
will appear as shiny areas on the surface (Fig. 11). Some WRPs are formulated with nondrying oils that
act as solvents (such as paraffin oil). These oils penetrate the wood but do not dry. They protect the wood
from degradation and mildew attack as do other types of WRPs. Since the oils do not dry, the wood
surface may remain oily until the finish absorbs. Absorption usually takes several days, depending on the
application rate and porosity of the wood. Since the oil does not dry, there is the possibility of tracking it
indoors if this finish is used on decks. These products are easy to apply to decks and have about the
same durability as other penetrating clear finishes.
Preparation of Water-Repellent Preservatives
Although directions for mixing a WRP were published in 1978, this formulation was possible only because
of the availability of pentachlorophenol (penta).1 This pesticide is no longer available to the consumer. In
addition, the fungicides listed in Feist and Mraz (1978) are usually unavailable. Therefore, it is not
possible for the consumer to formulate a WRP. A wide variety of commercial finishes are available, and
many of these contain effective mildewcides.
Resistance to Decay and Mildew
Water repellents and WRPs are effective when used on wood exposed outdoors above ground. In areas
where decay is a serious problem or where wood will be in contact with the ground (wood foundations or
fence posts, for example), wood will need far more protection than that afforded by surface treatment with
a WR or WRP. In such cases, wood properly protected by treatment with a commercial preservative is
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recommended. Such pressure-treated wood is normally available at lumber yards and should conform to
recognized standards for maximum service life.
For naturally decay resistant wood species, WRPs provide mildew resistance for both the heartwood and
sapwood; if the lumber contains portions of sapwood, treatment with a WRP is essential to provide
aboveground decay resistance.
Treatment with CCA provides resistance to decay only, not mildew (Fig. 9). Treatment of the preservativetreated wood with a WRP provides resistance to mildew. The WRPs also provide aboveground decay
resistance for sections of the wood that did not take the preservative treatment (heartwood) and the
interior of large cross sections exposed by cutting or drilling.
A number of commercial wood treaters are using a combined WR–CCA treatment for 5/4 by 6 in. (32 by
152 mm) radius edge decking. This lumber is marketed under trade names such as Ultrawood, Wolman
Extra, MELCO, and Weathershield. This dual treatment gives the wood more resistance to weathering.
Since the process is quite new, the durability of the WR treatment is not yet well established. Although the
WR is supposed to thoroughly saturate the wood, the wood may nevertheless require periodic
maintenance with a WRP. In addition, the commercial preservative treatments do not contain a
mildewcide, so added treatment with a WRP is necessary to prevent mildew growth. These treatments
should improve the wood characteristics and extend the product service life, particularly with regard to
weathering (i.e., surface checking, cracking, splitting, and erosion).
Safety
Care should always be exercised in applying a WR or WRP. The solvent-borne formulations are volatile,
flammable mixtures. Do not breathe their vapors or expose the solutions to flame or sparks. It is wise to
wear protective clothing on the hands and arms and to take care that the solution is not splashed in the
eyes or on the face. Be especially careful using a WRP because these solutions contain fungicides, some
of which are toxic. If rags, paper towels, and uncleaned brushes and rollers containing finishes are not
disposed of properly, they can spontaneously ignite. Store finishes in original containers in a locked
___________________________________________________________________________________ 1
(Feist, W.C., and Mraz, E.A. 1978. Wood finishing: Water repellents and water-repellent preservatives.
Research Note FPL-0124 (revised). Madison, WI: USDA Forest Service, Forest Products Laboratory)
Caution: Wood preservatives can be injurious to people, animals, and plants. Therefore, for safe and
effective usage, it is essential to follow the directions and heed all precautions on container labels. The
application of preservatives using any spray method can be especially hazardous and extra precautions
must be taken. Avoid spraying whenever possible. Do not use any preservatives indoors unless they
have been specifically approved and recommended for such use.
space, out of reach of children and pets, and away from foodstuff. Use all finishes selectively and
carefully. Follow recommended practices for the disposal of surplus preservatives and preservative
containers. Immerse finish-contaminated materials in water, then seal in plastic or an empty paint can
until they can be disposed of by proper incineration or burying.
Finish Application
A WR or WRP can be applied to all exterior wood that is normally painted. It can usually be used as a
pretreatment for paint or as a stand-alone finish. The stand-alone finishes generally have a higher wax
content. If you use a WR or WRP as a pretreatment for paint, be sure to read the manufacturer's
recommendations. Not all WRs and WRPs can be used as pretreatments for paints. Water-repellent
preservatives are usually intended for exterior use because the preservatives or fungicides in them are
toxic to humans, animals, and plants. Solvents and other additives may also be harmful. It is important to
read the label on the original container carefully to determine if the material is allowed and recommended
for indoor use. When in doubt, consult the manufacturer to determine which fungicide was used in the
WRP and whether it is appropriate for your proposed use. Be sure to follow the manufacture's directions
for temperature limitations because finishes do not cure properly if the temperature is too low.
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Procedures for Unpainted Wood
Water repellents and WRPs can be applied to wood by brush, roller, or spray, or the wood can be dipped
into the finish. A WRP can be used as a natural finish on many wood species to help maintain their
natural appearance. For example, finishing western red cedar with a WRP brings out the golden-tan color
of the wood. This finish is not recommended for exterior or brushed plywood. Treatment with a WR or
WRP will be more durable on weathered or rough-sawn surfaces because such surfaces absorb a greater
quantity of the finish than does a smooth surface. During the first few years of exposure, the natural color
of the wood can be partially restored by scrubbing the surface with a wood brightener–water mixture,
such as aqueous solutions of household bleach or oxalic acid or a commercial wood cleaner. Scrub the
wood with a stiff bristle brush and rinse thoroughly with water. Allow the wood to dry for several days
before refinishing. However, if the wood has been exposed for several years without a finish, it may not
be possible to restore the wood to its original color. Using a wood brightener may return some original
color and remove the mildew. The amount of color that returns depends on how much the surface has
weathered.
Regardless of whether the wood is unfinished or finished, particular care should be taken to apply a
liberal amount of the WR or WRP to the ends of boards, at joints between boards, and to all newly
exposed wood such as drill holes. Capillary flow will cause water to climb the back of bevel siding from
the lap joints. This flow of water can be prevented by applying WR or WRP to the lap joints. In addition,
the finish should be applied to the butt ends of horizontal siding; edges and top and bottom ends of
vertical siding; and edges and corner joints in window sashes, sills, window frames, doors, and door
frames. Bottoms of doors and window sashes are often overlooked. These are areas where water can
penetrate deeply and cause extensive damage if the wood is not treated. Treatment with a WR or WRP
will eliminate many such problems.
New Wood
Applying WR or WRP solution to the surface of unfinished wood by brushing or dipping is an effective
treatment for siding and exterior millwork (doors, window sashes, door and window frames, sills,
moldings, and fascia), wood fencing, and lawn furniture. Millwork is often dipped in a WRP during
manufacture to improve its durability. If treated millwork has been purchased, only freshly cut surfaces
need to be brush- or dip-treated. Dipping is more effective. Care should be taken to treat ends of boards
and joints between boards.
Refinishing
The weathering of wood finished with WRs and WRPs is similar to that of unfinished wood. The surface of
the wood degrades but at a slower rate than that of unfinished wood. Timely refinishing is essential to
avoid excessive wood degradation. Smoothly planed wood surfaces often require cleaning and
retreatment after the first year of exposure. After this maintenance, refinishing is required only when the
surface starts to show uneven discoloration or small black spots, which indicate mildew.
Specific Applications
Decks
A WRP is an effective finish for a fully exposed deck. Although the deck will need to be refinished
frequently, there is no need for laborious surface preparation, as is required by film-forming finishes.
Annual refinishing can be done quickly using a brush, roller, or pad. Brush application works the finish
into the wood better than do other methods. The finish should be applied liberally to decay-prone areas
around fasteners and end grain.
Treated Wood
Wood that has been pressure treated with waterborne chemicals such as CAA can easily be finished with
a WRP if the wood is clean and reasonably dry. If the wood is still waterlogged from the preservative
treatment, it should be allowed to dry for several days once the structure is built. During summer weather
conditions, this is usually enough time for the wood to dry sufficiently to accept a WRP.
Marine Uses
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Docks and similar structures in marine environments are particularly susceptible to rapid weathering and
decay. Treatment with a WRP helps preserve wood in this environment.
Fences
Like decks, fences are fully exposed to the weather. Many fences are left to weather naturally. If a finish
is desirable, a penetrating finish such as a WRP or semitransparent stain that contains a mildewcide
should be used. Periodic treatment with a WRP can slow weathering and decay, thus prolonging the life
of the fence. In addition, a WRP will preserve the natural weathered appearance of the wood.
Roofs
Although wood shingles and shakes on standard buildings have been superseded to a great extent by
composition and asphalt-based shingles, they are still used in certain areas of the country and on
expensive homes. Wood shakes and shingles are often left to weather naturally if they are made from
durable species such as western redcedar. Depending on exposure and climate conditions, the wood
generally turns silver, dark gray, or dark brown. However, in warm, humid climates common to the
southern United States and on heavily shaded roofs, mildew, moss, and lichens can occur.
These conditions are also conducive to decay. A WRP protects the wood while preserving the natural
appearance. It is best to dip-treat the shakes or shingles before they are installed so that the backs and
butt ends absorb the finish.
The finish may be applied by dipping the shingles to at least two-thirds their length and then letting them
stand vertically until the finish has dried.
Pretreatments for Painted Wood
New Wood
Water repellent and WRP formulations to be used as
pretreatments for paint have less wax or other WRs
compared with those formulated for use without
paint. When used as a pretreatment before painting,
a WRP can be applied in the same way as when
used as a natural finish. Freshly treated wood must
be allowed to dry. If the treatment is applied with a
brush, allow 2 days of drying in warm weather before
painting. If the wood is dipped for 10 or more
seconds, 1 week of drying is necessary before
painting. If enough time is not allowed for most of the
solvent to dry from the wood and for the wax to
absorb, the paint applied over the treated wood may
not cure or bond properly. Open joints, such as in
siding, millwork, and fascia, should be caulked after
treating
with a WR or WRP but before priming.
Refinishing
When applying a WR or WRP to previously painted
wood, loose paint must be removed; the WR or WRP
should be brushed into the joints and unpainted
areas. Remove excess WRP from the painted
surfaces with a rag. Allow 3 days of drying in warm
weather before repainting.
Removal of Mold and Mildew
If mildew is present, pretreat the wood with a
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commercial cleaner or a chlorine bleach–water solution. Allow the wood to dry for 1 or 2 days before
refinishing.
Removal of Mildew
Commercially available wood cleaners work quite effectively to remove mildew and other stains on wood.
A mildew cleaner can also be made by dissolving 1 part liquid household bleach and some powdered
detergent in 2 to 4 parts water.
Suggested formula:
1/3 cup household detergent
1 quart (5%) sodium hypochlorite (liquid household bleach)
3 quarts warm water (1 cup = 0.2 L; 1 quart = 0.9 L)
Caution: Do not use a detergent that contains ammonia; ammonia reacts with chlorine-containing bleach
to form a poisonous gas. Many liquid detergents may contain other additives that react with bleach.
Service Life
The service life of WRs and WRPs is about 1 year on exposed wood surfaces. However, WRPs are
extremely easy to reapply to some structures, such as decks. Water repellents and WRPs absorb readily
into the end grain of lumber and can stop water absorption for many years. The effectiveness of
pretreatment of millwork with a WR or WRP has been confirmed in outdoor exposure studies. The
differences between WRP-treated and untreated window sashes and frames are significant after
exposure for 5 years (Fig. 12). The window sash had been dipped in a WRP for 3 min. This treatment is
similar to those used by most millwork manufacturers. The window units shown in Figure 13 are still being
tested after 30 years of exposure.
Window units treated with only a WR were in reasonable condition. Window units treated with a WRP that
had extra high water repellency had the best durability. The combined effect of a preservative and a good
water repellent was the crucial factor for long-term durability. Untreated window units decayed severely
and actually fell from the test fence after only 6 years of exposure (Fig. 14).
Concluding Remarks
Wood is the material of choice for many structures. As with any building material, how wood is used
depends on its properties, such as strength and stiffness, as well as its finishing characteristics and
maintenance requirements. Problems such as poor finish performance, mildew, checking and splitting,
and wood decay can be controlled with proper care and maintenance. Such problems can be avoided or
attenuated through knowledge about the factors that affect wood, particularly wood exposed outdoors. If
wood structures are given proper care initially and are maintained periodically, they can be functional and
structurally sound, as well as aesthetically pleasing, for decades. Water-repellent preservatives can be
used as natural finishes and can greatly improve the durability and appearance of wood exposed
outdoors. They can also be used as pretreatments prior to the initial painting of wood. The water repellent
improves the dimensional stability of the wood, and the preservative improves the mildew resistance of
the paint. These properties work in concert to extend the service life of the paint.
NOTES:
This manual is part of a series of manuals and classes that make up the Contractors Foundation services. Reproduction or distribution
of this manual (or any part thereof) without the prior written consent of Contractors Foundation is forbidden under penalty of law.
This manual is intended as a guide to help contractors avoid many common technical mistakes in the process of cleaning and sealing
wood. It is not intended to replace the instructions written by the manufacturer of your choice of any equipment, supplies, or materials.
This manual is not a Chemistry textbook. It is solely intended to give a contractors-eye view of the products that many of us
come into contact with each day. Contractors Foundation is not liable for your interpretation or use of any of the information
in this manual.
© 1999 - 2010, Contractors Foundation
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Note: We have decades of experience helping pressure washing companies like yourself and the entire
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Optimization, and some other special offers for you, just for purchasing this manual. All you have to do to
get access is to visit a special area on our web site at: http://contractorsfoundation.com/members/. The
information you learn through this free course alone will help you bring in more clients, and to outperform
your competition. For other benefits that you can take advantage of from the Contractors Foundation,
visit our website at: http://contractorsfoundation.com
© 1999 - 2010, Contractors Foundation
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