Mortar
Introduction
Mortars are used in residential building in the following areas:
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as a render on masonry
as a bedding agent in brickwork
as a bedding agent for ceramic tiles
as a bedding agent for roof tiles
as a grout for ceramic tiles
as a ‘topping’ mortar for concrete.
Learning outcomes
On completion of this unit, you should be able to:
•understand the role of lime and cement in the making of mortars
•define mortar and describe the purpose of mortars in the building
industry.
Lime
Lime for building purposes is obtained by burning (calcining)
carbonate of lime (limestone). The material is burnt in a kiln for two
to three and half days where moisture is driven off leaving rock or
quicklime. There are several types of kiln ranging from a simple
brick structure to an elaborate rotary type.
Lime is used as a component of mortars in brickwork, masonry and
plastering, both in render and setting.
Rotary kiln (hydrated) lime
This is obtained by crushing rock lime in a machine and then spraying it with
the exact amount of water required to slake it to a dry powder. This is then
conveyed to a separator from which the lime powder is blown off into a
storage bin, leaving the impurities behind. It is sold in 25 kg paper bags, with
40 bags per tonne.
Properties of hydrated lime:
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Convenient package size for handling.
Does not deteriorate rapidly when stored.
Ready for immediate use in dry form.
Quantities may be accurately gauged.
It is pure lime.
Hydration is complete, therefore it will not be subject to ‘blows’ in
mortar due to later expansion of lime particles.
Modern additives are now used extensively by ready mix mortar
manufacturers to produce a plastic or workable mix.
Portland cement
The process of manufacturing Portland cement was developed and
patented in 1824 by an English bricklayer named Joseph Aspin,
who named his product Portland cement because it resembled a
yellowish building stone being quarried at Portland, England.
Modern industrial developments have led to a Portland cement
which is no longer yellowish and therefore no longer resembles
Portland stone, at least in colour, although the basic process of
manufacture is still the same.
Process of manufacture
There are two methods used to manufacture Portland cement:
• the dry method
• the wet method.
A description of the two methods follows.
Dry method
• Limestone and clay or shale are finely ground.
• The two ingredients are carefully proportioned and mixed.
• The mixture is fired in a rotating cylindrical kiln. The burning temperature of the kiln is
2600°C– 3000°C. This causes a chemical change and produces a clinker consisting of
vastly different chemical compounds to the raw material. (The term ‘calcining’ does not
apply to Portland cement manufacture.)
• Gypsum is added to the resultant clinker and the mixture is finely ground again.
Wet method
This is similar to the dry method except that the initial grinding and mixing is done wet. Samples are
tested in the laboratory and blending is carried out as required to produce the correct recipe. The mix is
then injected into rotary kilns for burning. After burning the method is similar to the dry process.
Approximately 75 per cent of Portland cement produced in Australia is manufactured by the wet
process.
Approximately 11/2 tonnes of limestone and 11/4 tonnes of clay or shale are necessary to produce 1
tonne of cement.
Uses
There are several types of Portland cement which are used as binding
agents.
Type GP general purpose Portland cement
This cement is used in concrete for buildings or civil engineering structures
such as dams, bridges, roads, tunnels, airport runways, wharves and jetties.
It is also used in precast or prestressed concrete products such as building
components, both structural and architectural, bricks, blocks paving slabs
and garden ornaments.
Type HE high early strength Portland cement
This material has special qualities due to extra fine grinding and/or variation
in chemical composition by special selection and blending of raw materials.
Setting time and ultimate strength are about the same as normal Portland
cement. The cost is slightly increased.
Type LH low heat cement
This material liberates less heat during early setting and hardening than
types 1 or 2. It is used therefore in mass concrete to control temperature
rises in the concrete. It has somewhat better resistance to some forms of
chemical attack than types 1 or 2 because of its chemical composition.
Aluminous cement
Composition and manufacture of this type of cement are
considerably different to Portland cement. It is made from a mixture
of limestone and bauxite (bauxite is the principal ore of aluminium).
It is hydrated alumina.
Aluminous cement can be mixed with Portland cement to accelerate
the hydration process and produce a fast rate of strength
development.
Sand
Types of sand
Pit sand—beach or dune sand
This sand is suitable for use in mortar or concrete provided it is collected
from above the salt water level or washed to remove any salt (eg Sydney
or Botany sands).
Pit sand is generally white or cream. Grey sand is of inferior quality
because it contains dirt. Bush pit sand, yellow or brown in colour, shrinks
because of its 30 per cent or more clay content and is not recommended
for use.
River sand
Usually this is good quality clean sand but it is often made up of particles
that are smoother and/or coarser than good pit sand.
Crusher fines
This material is produced as a by-product in crushing rock. The particles
are rough and splintery in shape (hungry) and therefore require more paste
to produce a workable mix than natural sands.
Grading
A mixture of coarse and fine particles of sand used in mortar for
general purposes should pass through a 5 mm mesh sieve. All
particles passing this size are termed ‘sand’ (and can be used for
mortar) while those retained are termed ‘coarse aggregate’ (and can
be used for concrete). Clean sand available for building usually
complies with this rule.
Examination
Clean sand will not leave a stain on white cloth or on the hands
when rubbed together. Salt may sometimes be detected by tasting
water after a small quantity of the sand has been immersed in it. A
more reliable method is to use clean water to wash some sand in a
small vessel and then add nitrate of silver. Clouding of the solution
denotes the presence of salt.
Treatment of poor quality sand
Poor quality sand may be screened or sieved to remove lumps,
fine roots and stones. Dust, clay, vegetable matter and salt may
be removed by washing the sand under running water in a trough
or shallow tank.
Substitutes for natural sand
Crushed sandstone is suitable for mortar when free from dust and
clay.
Crushed furnace ashes or coke contains corrosive chemicals and is
not suitable for use with steel reinforcement. It is, however, good for
use in mortar exposed to low furnace heat such as in domestic
coppers, incinerators and barbecues.
Mortar
Mortar may be defined as
a mixture of an aggregate or bulk material and a matrix or binding
material.
Sand is the aggregate and lime and cement are the binding
materials. These materials are combined to form different types of
mortar mixtures in accordance with required strength.
Lime mortar
Lime mortar is a mixture of slaked rock lime or hydrated lime,
clean sharp sand and clean water. This is a comparatively soft
type of mortar of low strength.
Proportions are one part lime, 21/2 to 4 parts sand by volume and
sufficient water to bring the mixture to a workable plastic state.
Mixing on the job
Using hydrated lime
Powdered lime may be used directly with measured quantities of sand or it may be
soaked for 24 hours in a large drum to ‘fatten’. The lime, sand and water may be mixed
by hand on a clean hard surface or may be machine mixed.
Premixed lime mortar
This is widely sold by the truck load of 1.25 m3 or in drums for small jobs. It is
generally used for brickwork, when available, because of its convenience and the
reduced costs in relation to mixing on the site.
Cement mortar
Cement mortar is a mixture Portland cement, clean sharp sand, and clean water and a
small proportion of lime. This makes the strongest type of mortar.
Proportions are one part cement, 3 to 4 parts sand by volume 1/10 part lime together
with sufficient water to make a workable plastic mixture.
Mixing is usually done by hand or by machine on the job.
Plasticising agents of many kinds, other than lime, are frequently used to make cement
mortar more workable.
Cement mortar is best when used before the initial set takes place, normally about one
hour after mixing. Mortar re-mixed after the initial set loses some strength and should
not, therefore, be re-mixed for use.
‘Compo’ or lime-cement mortor
This medium strength mortar is a mixture of lime, cement, clean sharp
sand and clean water. It sets harder than lime mortar but not as hard as
cement mortar.
The standard mixture consists of either one part cement, one part rock or
hydrated lime and 51/2 to 6 parts sand, or one part cement, 2 parts rock or
hydrated lime and 8 to 9 parts sand with sufficient water to make a plastic
workable mixture. Quantities of materials should be carefully measured and
either hand mixed or machine mixed.
Mortars of all types may be coloured red, brown, black, cream or green by
adding mineral oxides in dry powder or liquid forms.
Grout, a thin or liquid mortar (usually cement) used for filling up joints. An
excess of water makes the mortar weak. Where strength is required,
additional cement is added to the grout. It is preferable to wet the work and
allow the water to soak in before grouting.
Bush sand
In some areas (such as Sydney) ‘bush’ sand and cement are
mixed to produce a bricklaying mortar, in a ratio of 1:5. Bush
sands contain a clayey loam which produces a very workable mix
but which is susceptible to shrinkage. For low level residential
work this does not pose any real problems.
Additives or admixtures
Proprietary admixtures are available for mortars and usually take
the form of air in training agents and are used to make the mix
more ‘plastic’ and easier to use.
However, caution should be observed with the use of all
admixtures as they are often used contrary to the manufacturers’
recommendations and their effects are often misunderstood by the
users.
Summary
Portland cement and lime are generally used on building projects in bagged
form and mixed on site. Their main use is on residential projects, including:
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mortar for bricklaying
render for masonry walls
bedding mortar for ceramic tiles and roof tiles
as grouting material.
The strength of mortars varies widely according to the ingredients used.
Cement mortars are stronger than lime mortars and are more widely used
today.
Portland cement and hydrated lime are factory produced.
Sands are excavated, washed and graded according to local supplies. Water
for mortars should be clean and free of organic material. Water gives
plasticity to the materials and in the case of cement, it is essential to the
hydration process and resulting strength.
Properties of Metals
Introduction
Metals have been used by humans for over 6000 years. The first metals
were simply picked up off the ground, but in time people learnt to extract
metals from their ores. Nowadays the technology has become quite
complex and not only can many metals be extracted from their ores, but the
properties of metals can be modified by various types of finishing
processes or by mixing with other metals to form alloys. For building
purposes, most metals are alloys.
The major base metals used are iron, copper, lead, zinc and aluminium.
Metals using iron as their base are called ‘ferrous’ metals while the others
are termed ‘nonferrous’. Brass is an important nonferrous metal used in
building, being an alloy of the base metal copper.
Glass today is manufactured from the same materials as it was several
thousand years ago. Egypt is credited with the earliest glass making
technology at least as early as 4000 BC. In Australia commercial glass
making began in 1872 in Melbourne with bottle manufacture. In 1903
factories were established and in the 1920s and 1930s products were
increased to include window glass. Glass is manufactured commercially
from sand (silica), soda and lime. Its characteristics are dependent on the
proportions and treatment.
Learning outcomes
On completion of this unit, you should be able to:
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identify and name the metals commonly used in the residential
building industry
understand the effects of the incompatibility of metals
state the application of the different metals used in building
list the different types of glass available to the building industry
state the uses of glass in residential building.
Properties of metal
Metals are substances that can either be hammered (the quality called
malleability) or drawn out as wire (the quality called ductility) or melted and
formed into shapes in moulds. Most metals can be polished. All metals are,
to greater or lesser degrees, conductors of forms of energy such as heat and
electricity.
Other characteristics possessed by metals may vary considerably from
metal to metal. Some metals (eg stainless steel) have good strength
qualities, whereas others (eg tin) have very little strength. All metals,
however, will lose strength when repeated force is applied to them—a
process known as metal fatigue.
The degree of hardness of a metal will vary according to its natural
characteristics (lead and tin, for example, are soft metals; chromium and
nickel are hard) and according to the degree to which the metal is worked.
When a metal is worked at normal temperatures (by being rolled or forged,
for instance) the result will be an increase in its hardness and strength—this
it called work hardening.
Properties of metal
Most metals are subject to corrosion, which occurs when the
surface of the metal combines with oxygen in the air to form a coat
or crust that is no longer metallic (eg rust on iron or steel). Corrosive
liquids and gases can actually eat away metals. (We can see the
effect of salt air or spray on aluminium.) The process of corrosion is
usually greatly speeded up by the action of heat and moisture.
Some metals have very low corrosion-resistance, while others have
a good degree of corrosion-resistance. Metals with a high degree of
corrosion resistance (eg chromium) are often used either as
coatings or in alloys with other metals to increase their resistance to
corrosive agents.
Forming metals
How metals are formed depends upon the type of metal, the objects being
made, and whether parts made of other metals are also incorporated. The
following are some of the methods used:
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Casting — where molten metal is poured into moulds and
allowed to cool and harden. Rolling hot or cold metal is rolled
between heavy rollers to produce various bars, strips, sheets or
sections of metal.
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Forging — where hot metal is squeezed into shape, often using
mechanical hammers and suitably shaped dies.
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Extrusion — where heated metal is forced through a suitably
shaped hole in a hardened steel die to produce continuous solid
or hollow sections.
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Drawing wire — or tubes are pulled through tapered dies to
reduce the thickness of the metal. Normally the metal is cold and
the process lessens its strength.
Joining metals
Metals can be joined by a variety of methods, including the following.
• Mechanical joints: Bolts, screws or rivets are used to join metal
components together.
• Soldering and brazing: Most metals can be joined using an alloy which
is a mixture of two or more metals that melt at a lower temperature than
the melting point of the metals being joined. Soldering usually refers to
tin-lead and lead-silver alloys which melt below 300°C.
• Brazing: Gives stronger joints than soldering; however, as it is done at
higher temperatures (over 600°C), brazing cannot be used on metals
such as lead which have low melting points.
• Welding: Most welding involves a metal being heated to a temperature
below its melting point, and the soft metal being hammered together.
This traditional blacksmithing method has been replaced by gas welding
(using oxyacetylene or propane) and arc welding (using an electric arc
struck between the work and a welding rod or a carbon electrode).
• Both brazing and welding involve heating the adjacent metal to
extremely high temperatures which allow the metal to flow together and
form one continuous unit.
Ferrous metals
Ferrous metals are those metals that contain a large amount of iron.
The main types of ferrous metal are:
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cast iron
wrought iron
steels.
Manufacture
Iron ore, as mined, is a combination of iron and oxygen and various other
substances. In this country most of the ore is obtained from open-cut
mines.
The first step in processing the ore is to reduce it to metallic iron (often
called ‘pig iron’), a process carried out in a blast furnace using coke as a
fuel and reducing agent. The metallic iron, at this stage, contains a
relatively high proportion of carbon (about 4 per cent).
To make steel, the carbon content of the metallic iron must be lowered to
less than 1 per cent by an oxidation process in the steelmaking furnace. At
the same time, the metal is given whatever special chemical and physical
properties may be required by the addition of other metals. The quantities
and timing of the additions of carbon and various other elements are
carefully controlled to make the wide range of irons and steels that are
available.
Effects of added elements
Carbon is the principal hardening element in steel. In plain carbon steels, it is
used as the controlling element to regulate physical properties. When the
carbon content is increased, hardness and tensile strength are improved but
ductility and weldability are reduced (see Figure 7.1).
Figure 7.1: Influence of carbon on the properties of ferrous metals
Effects of added elements
Manganese increases strength and hardness but to a lesser degree
than carbon. It also improves the toughness and abrasion
resistance of steel.
Chromium increases hardening ability and tensile strength and
improves corrosion and abrasion resistance. It is usually associated
with nickel additions to form ‘stainless steel’.
By-products an recycling
Blast furnace slag
Blast furnace slag is the waste from the smelting process. It is an important
by-product which can be used for concrete aggregate, road metal and slag
wool for insulation.
Steel scrap
This is a major source of metallic iron for steel making. Scrap may either be
residue left from the steelmaking process or purchased from discarded or
obsolete constructions. About half of the crude steel produced annually in
the world will eventually be returned to the steel-making furnaces.
Cast iron
Cast iron is produced by re-melting pig iron with steel and cast iron scrap.
The cast iron has a high carbon content which makes it free-running and,
therefore, very suitable for moulding intricate shapes. Cast iron has been
used in the past for the decorative iron lace on buildings which is often
wrongly called ‘wrought iron’. Cast iron is used for fire grates; for soil waste
pipes and ventilating pipes; for drainage gratings and frames; and for baths
and basins (with a vitreous enamel finish).
By-products an recycling
Wrought iron
This is a low carbon iron which is excellent for forging but cannot be
cast, tempered or welded (by gas or arc). Wrought iron was very
popular for decorative finishes (such as balustrades and balcony
railings) in the 1950s but has since lost popularity.
Steels
Steels are produced by removing impurities from pig iron and then
accurately adjusting the quantities of all the ingredients. Steels are
noted for their high strength compared to their production costs, and
also for their poor performance in building fires. Ordinary steels do
not resist corrosion well, but special steels (eg stainless steel) are
produced today with excellent corrosion resistance.
Structural steel
Structural steel products are
available in hot rolled sections and
cold formed sections.
Hot rolled sections
These are formed while the steel is
at elevated temperatures and
include the following profiles:
Cold formed sections
These are formed while the material is cold as distinct from
materials that are shaped or worked while under the effect of heat.
Unlike hot rolled sections, cold formed sections have constant
thickness.
Cold formed sections may be formed by:
Rolling in a rolling mill (for material up to 20 mm in thickness), the
product being what is known as ‘cold rolled sections’ (see Figure
7.2).
Figure 7.2: Rolling in a rolling mill
Cold formed sections
Pressing by means of a press brake (for material up to 20 mm in
thickness), the product being what is known as ‘pressed steel
sections’ (see Figure 7.3).
Figure 7.3: Pressing with a press brake
Cold formed sections
Pressing by means of a swivel bender (for material up to 30 mm in
thickness)—the product being what is known as ‘pressed steel
sections’ (see Figure 7.4).
Figure 7.4: Pressing with a swivel bender
Use of structural steels
Pressed steel
Pressed steel is used for:
 door and window frames
 metal trims (such as skirtings)
 wall panels.
Note: Pressed steel sections are limited to the size of the break
press; or, with swivel bending, are able to be produced economically
in small quantities.
Alloy steels
Alloy steels contain certain added elements that provide special properties
such as ultra high strength or resistance to corrosion or heat.
Stainless steel (containing chromium and nickel) is one such steel alloy
which, although much more expensive than mild steel, is being increasingly
used in building in a wide variety of applications because of its durability
and low maintenance needs (even under extreme conditions of
atmospheric pollution, as it has excellent resistance to corrosion).
Stainless steel has outstanding structural advantages because its hardness
and toughness allows it to be used in very light sections, thus reducing
greatly the weight of finished articles. Even more importantly, it is less
affected by extreme heat, such as in a fire.
Except for very simple cutting or drilling on site, all shaping and fitting of
stainless steel must be done in suitably equipped factories and workshops.
Stainless steel is also used for sanitary ware (eg sinks and benchtops).
Prevention of corrosion in steel
Upon exposure to the atmosphere ferrous metals combine with
oxygen to form a red oxide (ie rust). Rust corrodes the metal and
eventually wears it away, leaving behind a red powdery residue.
This not only affects the appearance of the metal but substantially
reduces its strength.
One way of making steel rust resistant is by applying one of many
protective coatings available for steel products. These fall roughly
into two groups: metallic coatings and non-metallic coatings. As
most require scrupulously clean conditions and special surface
preparation of the steel for successful application, factory
application of surface coatings is preferable.
Metallic protective coatings
These function by taking advantage of electro-chemical differences
between different metals. In adverse atmospheric conditions it is the
surface coating that is sacrificed rather than the base metal.
A number of methods are used to apply metallic coatings, such as
electroplating, spraying and hot dipping. Metals used to coat the
steel include cadmium, zinc, tin, aluminium and copper.
Zinc aluminium alloy applied by the hot dip process has effectively
replaced galvanised steel in applications such as roofing because of
its greatly increased durability.
Non-metallic coatings
These are available in a wide variety of colours and include:
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paints
baked epoxy finishes
vinyl coatings
bituminous coatings
vitreous enamel coatings.
Baked epoxy finishes are applied to zinc-aluminium coated steel
which is chemically treated to assist bonding. An epoxy primer and
then the final colour coat are baked on separately. This type of finish
is popular for domestic and commercial roofing and wall cladding for
normal conditions.
Non-metallic coatings
In marine and polluted industrial conditions steel can be coated with a tough
vinyl which is laminated to the steel substrate. The vinyl coating locks out
moisture, making an extremely corrosion-resistant finish.
Vitreous enamel coatings comprise a layer of glass fused to a properly
prepared steel base.
Painting should be considered as a complete system that includes surface
preparation, pre-treatment to facilitate adhesion, primer, intermediate coat or
coats and finish coat. Different types of steel require different pre-treatments
and coatings.
Bituminous coatings are based on bituminous resins such as coal tar or
asphalt. The bituminous resins perform well underground and in contact with
water but do not have good weather durability when exposed to sunlight.
Nonferrous metals
Most nonferrous metals are more costly to produce than ferrous
metals. However, they often have much better working properties
and resistance to corrosion. The more common nonferrous metals
are copper, aluminium, zinc, lead, nickel, tin and cadmium.
Copper
Copper has been in use for at least 10 000 years: nearly 5000 years
ago it was being beaten into sheets, pipes, and other building
products.
Copper is a pinkish coloured metal and is easily hammered into
sheets. It is much more expensive than some alternatives but its
extreme resistance to corrosion outweighs this disadvantage in
certain applications. Upon exposure to the atmosphere, copper
forms a protective copper oxide coating which is light green in
colour.
Uses
Its resistance to corrosion has made it popular for use as water
pipes and tanks. It also conducts electricity very well, hence its use
for electrical wiring. Other uses include roofing, roof plumbing,
flashing and damp courses
Brass
Brass is an alloy of copper and zinc, and is an attractive golden
colour.
Uses
Brass is used for plumber’s hardware (eg pipe connectors and
fittings; taps and outlet spouts, often chrome finished). Screws,
nails, grilles, hinges, door locks and latches and chains are often
made from brass.
Aluminium
Aluminium is a light-weight metal (approximately one-third the
weight of iron) and is silver-white in colour.
Aluminium was introduced as a building material after World War
Two in competition with traditional building metals, such as steel
and copper. Probably the major characteristic that has helped
aluminium gain widespread acceptance in the building industry is
its suitability for extrusion production methods. This means that
very complicated shapes can be produced economically.
Uses
Aluminium products are extensively used in the building industry—
for domestic windows, doors and insect screens; for commercial
windows and curtain walls for residential and industrial roofing and
rainwater goods; for balustrades and railings and for reflective
insulation.
Corrosion resistance
One of the most significant properties of aluminium is its excellent
resistance to atmospheric corrosion. On exposure to the
atmosphere, a whitish coating of aluminium oxide forms which then
protects the surface from further corrosion. The structural integrity is
not impaired as a result of this process.
Thus, untreated aluminium can be used for roofing, cladding and so
on, but where long-term appearance is important the aluminium
should be finished.
Compatibility with other building materials
Corrosion of a metal may be accelerated through contact with
another metal of very different electro-chemical properties especially
in the presence of an electrically conductive solution, such as sea
spray or industrially polluted moisture.
Copper, brass and nickel alloys, all have a large potential difference
to aluminium and in a salt solution cause it to rapidly corrode.
Some other building materials are also incompatible with aluminium
and direct physical contact with those materials should be avoided
or barriers should be used. Table 7.1 broadly indicates the types of
barriers suitable for most building construction applications.
Finishes for aluminium
Although aluminium is naturally corrosion resistant, various finishes may be applied for
aesthetic reasons. These include textured finishes ranging from a fine satin finish
(achieved by chemical etching) to a scratch-brushed or hammered finish.
Bright finished aluminium can be achieved mechanically or chemically and results in
highly reflective product. To retain the desired appearance, however, the sections
should be anodised immediately.
Anodising is an electro-chemical process which greatly increases the thickness of the
protective oxide film which would naturally form on the surface, thereby increasing the
resistance of the surface to corrosion and damage and enhancing the appearance of
the finished product. Film thicknesses can be specified for different applications.
The oxide film may be artificially coloured. Depending upon the process, however,
some colours may be subject to ultraviolet deterioration and therefore are only suitable
for interior applications.
Paint may be applied to aluminium but factory application is recommended as the
process must be carried out in a dust-free environment and the aluminium surfaces
must be pre-treated to remove surface contaminations and to provide a key for good
adhesion. Powder coating is now widely used as a finish to aluminium in residential
building.
Methods of joining aluminium sections
Most physical joining of aluminium elements is achieved with the
use of bolts and nuts, screws, nails and rivets. For reasons of
compatibility, fasteners are normally aluminium alloy, stainless steel
or cadmium-plated steel.
Some modern adhesives such as epoxy and epoxy-PVC types are
commonly being used to produce high-strength joints between
aluminium and a great variety of other materials.
Welding is also used to join aluminium. If welded assemblies are
subsequently anodised, some discolouration in the anodised film
occurs across the welded zone.
Zinc
Zinc is a soft, greyish metal which can be hammered or rolled into
sheets: such sheets have been used for roofing rainwater goods.
Today, zinc’s most important function in the building industry is as a
protective coating on steel.
The zinc coating acts first as a barrier to corrosion. However, should
the coating be scratched or damaged, exposing the steel, the zinc
surrounding the damaged part will itself corrode instead of the steel.
Thus by sacrificing the zinc the steel is protected and will not rust
until all available zinc is used.
Zinc-aluminium coating
Research has produced a protective coating for steel which
combines zinc and aluminium in an alloy. It is easily applied, by hot
dipping, and holds to the metal better than zinc galvanising, thus
giving much better protection. It is used on sheet steel and cladding.
Lead
Lead is soft and easily worked, but its great density makes it heavy to
handle, and thin sheets and pipes will not even support their own weight.
Lead has been used for thousands of years: lead water pipes were used by
the Romans, and our word ‘plumber’ comes from the Latin word plumbum
meaning lead.
Due to its toxic properties, however, lead is no longer used for water pipes.
In the past, it was used for roofing and roof plumbing, but today its use is
limited—although in certain roof plumbing situations, its weight and
malleability still make it a useful and preferred material.
Uses
Lead is used:
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for flashing and damp coursing
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for solder (as an alloy with other metals)
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as sheet lead lining for sound proofing.
Nickel
Nickel is a hard, silvery-white, malleable metal. It is resistant to
corrosion.
Nickel is used:
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on steel as a base for chromium plating
as a constituent of stainless steel
as a nickel alloy (known as ‘Monel metal’).
Tin
Tin is a very costly, soft, weak metal with a low melting point
(232°C), but extremely resistant to corrosion.
Uses
Tin is used:
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as a coating on sheet steel (tin plate)
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for solders.
Cadmium
Cadmium is a white, malleable metal that looks like tin.
Uses
Cadmium is used:
• for electroplating steel components (such as screws, latches,
handles, locks)
• as plating on brass plumbing fittings, locks, latches, handles and
other such fittings.
Chromium
Chromium is well known for its high resistance to corrosion as a
plating, and as a constituent of stainless steels and other corrosionresistant alloys. It is extremely hard and scratch resistant.
Stainless steel
Stainless steel is far harder than mild steel and silvery in
appearance. It has wide applications in commercial buildings and
has been used extensively for domestic sinks. More recently it has
been used for bench tops and as a termite barrier where it takes the
form of a very fine mesh which termites cannot penetrate.
Metal frame construction
Domestic and commercial
buildings can both be of
metal frame construction.
This type of construction is
versatile, light, strong,
time and labour saving,
economical, and stable.
Walls, roofs and floors can
all be constructed this
way.
The metal frames made
from steel are prefabricated in the workshop
or before being erected.
They can be joined
together using rivets,
welds, screws or bolts.
Figure 7.6: Metal framing for a brick veneer house
Fasteners
The wide range of metal fasteners used to join or fix building
materials and components includes:
•
•
•
•
nails
screws
bolts, nuts and washers
timber connectors and framing anchors
•
masonry anchors.
Screws
Screws are available in a range of sizes, shapes and coatings for
use with wood or masonry.
The four most common types of wood screw are:




countersunk head
round head
raised head
coach screws (see Figure 7.8).
Bolts, nuts and washers
Bolts, nuts and washers are normally made of plain steel, alloy steel
or a non-ferrous metal, and may have a protective metal coating
(such as zinc or cadmium). The bolt heads are usually either dome
headed with a square shank; dome headed with a slot; hexagonal or
square headed. The nuts may be square or hexagonal and the
washers are flat discs with a cental hole. The two most common
types of bolt are:
•
•
the coach (or cup head) bolt
the hexagonal head bolt (see Figure 7.9).
Timber connectors and framing anchors
These are used for joining various timber-framing members. They
are made from hot-dipped galvanised steel and are strong and quick
to install. Figure 7.10 illustrates some of them, together with their
methods of fixing.
Masonry anchors
Masonry anchors are used in concrete or masonry. A strong fixing is
provided by the casing expanding into the hole as the nut or bolt is
tightened. A masonry anchor may be placed into a mortar joint but is
far more effective if placed in the body of the masonry.
The two most common types are:
•
the ‘Loxin’
•
the ‘Dynabolt’ (see Figure 7.11).
Glass
Manufacture
The art of glass-making is very old and, today, the industry still uses
basically the same raw materials as the ancient glass makers.
These basic ingredients are:
 silica (from sand)
 soda (sodium carbonate)
 lime.
With the addition of varying quantities of:
 dolomite
 feldspar
 soldium sulphate
 cullet (broken glass)
 decolourising or colouring agents.
The major constituent, silica, is the glass-former while the other minerals
act as fluxes and refiners in the melting process. The raw materials are
mixed together and melted at approximately 1500°C and then cooled to a
workable temperature of about 1000°C, finally hardening at about 500°C.
Glass used in building
Different applications require glass of different thicknesses and
properties. The sheet size of the glass area is important: for
instance, larger windows require thicker sheets of glass, both for
self-support and to resist pressure from wind loads.
Glass is specified by its thickness, method of manufacture and
function. Information is readily available from the manufacturers.
Glass used in building
Glass used in building falls into the following categories:
• float glass
• sheet glass
• plate glass
• toughened glass
• heat absorbing glass
• light and heat reflecting glass
• patterned or figured glass
• laminated glass
• wired glass.
Float glass
Floating is the most common modern method for the production of
high quality glass for building. It involves a continuous process in
which the molten mixture passes to a float bath where it is
supported on molten tin. As the ribbon of glass passes through the
float bath it is slowly cooled and fed onto rollers (see Figure 7.12).
Sheet glass
This is an older method which produces transparent glass that is not
perfectly flat. A ribbon of molten glass is drawn between rollers
through a cooling chamber (see Figure 7.13).
Plate glass
This method has been largely superseded by the float glass
method. It produces a greater range of thicknesses than the drawn
sheet method because the process is continuous. The molten glass
is drawn between metal rollers and then between a twin grinder unit
which polishes both surfaces simultaneously.
Toughened glass
This is produced from ordinary glass by thermal treatment of the
finished product. The resultant surface tension across the sheet
causes the glass to fracture into small particles when cut so that
once the glass product is so treated it cannot be further modified or
cut on site. Toughened glass is three to five times stronger than
ordinary glass with regard to sustained loads and impact but the
surface is no harder than ordinary glass. This type of glass is
commonly used for frameless glass assemblies.
Heat absorbing glass
This is produced by the addition of certain minerals during melting. It
significantly reduces solar heat gain and glare in a building by
absorbing between 50 and 90 per cent of the infrared rays and 30
and 75 per cent of the visible light rays. As a result, this glass tends
to expand and contract more than other types of glass and suitable
tolerances must be left in the frame sizes. Heat absorbing glass is
available in a small range of tints.
Light and heat reflecting glass
This is produced by coating the glass surface with metallic films.
With the use of this glass, solar radiation can be reduced by up to
70 per cent. Frequently this glass forms part of a double-glazing
system which protects the coated surface.
Patterned or figured glass
This is produced by passing a ribbon of molten glass between
rollers during the cooling process so that a pattern is pressed into
the glass.
Laminated glass
Glass layers are bonded together by heat with a polyvinyl butyral
interlayer between the glass layers. This technique produces
shatterproof and safety glass such as bullet-proof and cycloneresistant glass, one-way glass and heat and light reflecting glass.
Wired glass
Wired glass incorporates a layer of the fine wire mesh and is an
earlier form of safety glass used for industrial glazing, balustrades,
shower screens and so on. It is also used as a fire-retardant glass in
some situations.
Properties of glass in buildings
Thermal performance
Glass expands and contracts on heating and cooling and, to prevent the
kind of disasters which happened with early glass curtain-walled
skyscrapers, this should be taken into account in the design.
Stresses can be set up in the glass resulting from differences in expansion
rates between frames and glazing, especially where frames are metal.
Thermal insulation
Single glazing offers little thermal resistance but the effect of an air gap
created by double glazing almost halves the heat loss through a single
pane.
The optimum gap is about 20 mm. Heat absorbing and reflecting glasses
make an effective contribution to minimising solar heat gain (see Figure
7.14).
Properties of glass in buildings
Acoustic performance
For any degree of sound insulation, double glazing is essential.
Sound reduction values vary according to the thickness of the glass
and the width of the gap.
Fire resistance
Although non-combustible, ordinary glass breaks and then melts in
fires and double glazing offers no significant advantage over single
glazing. Certain special glasses offer some degree of fire
resistance.
Alternative glass products
Glass fibres
Glass fibres are very strong and flexible for their size. They are used in
electrical elements and insulators. In addition, their transparent or
translucent qualities make them suitable for globes and light shades.
Electrical goods
Because of its high electrical resistance, glass is frequently used in
electrical elements and insulators. In addition, its transparent or
translucent qualities make it suitable for globes and light shades.
Glass bricks
Glass bricks can form a semi-transparent wall which is self supporting but
not structural. This was a popular building material prior to World War Two,
at which time production was interrupted, but it is again becoming popular.
Recycled glass products
Much glass-making involves the recycling of old glass but glass products
have been used in alternative ways as building materials. Glass bottles, for
instance, have been built into walls. When filled with water, such walls can
act as heat storage banks which can be seasonally adjusted.
Summary
Metals
Metals are widely used in the building industry. Some common metals and
their applications are:






steel—framing and cladding materials
lead—flashings
copper—plumbing pipe and fittings and electrical cable
brass—tapware and pipe fittings, door hardware
zinc—protective coatings
aluminium—window and door framing, roof cladding.
Some metals require protective coating to fulfil their service. Steel and
aluminium in particular have to be protected from corrosion by the elements
and generally most metals should not be allowed to come into contact with
each other.
Summary
Glass
Glass is manufactured from silica, soda and lime. Different
applications require glass of different thicknesses and properties. In
particular, larger sheet sizes will require thicker glass to resist
pressure from wind loads. Glass is specified by its thickness,
method of manufacture and function.
The main use of glass in building is for windows but other functions
include lighting and translucent bricks.
Timber
Introduction
On the successful completion of this course, you will
have achieved a Statement of Attainment for units:
• BCGBC4006A Select Procure and Store construction
materials
• BCGBC4007A Plan building or construction work
• BCGBC4008A Construct on site supervision of a
building or construction project
Introduction
Learning outcomes
On the completion of this unit you will be able to:
•
•
•
•
Understand the basic characteristics of wood
Determine the factors that affect the durability and
strength of timber
State the main causes of defects in timber
Classify the main types of timber and manufactured
boards according to their use.
Tree growth
Introduction
A tree trunk is really a very long cone, not a cylinder
(see Figure 2.1 in the guide). The height increase in
the trunk or lengthening of a branch is due to growth at
the extreme tips.
The trunk does not get longer between branches; it
gets thicker to support the weight of the growing tree.
Cells under the bark produce this thickening of the
trunk.
In cool climates there is a definite seasonal pattern in
softwoods and hardwoods, and this is often seen in the
growth rings. Counting growth rings can be used as a
rough guide to the age of a tree, but the accuracy of
this method can be affected by drought, by irregular
growth conditions and by where the sample is taken in
the trunk.
Introduction
Sapwood and Heart wood
Sapwood
Sapwood extends from the growth cells under the bark,
(the cambium layer) into the trunk for a short distance. It is
made of newly formed wood cells which contain food
(including starch) and water.
Heartwood (or truewood) see Figure 2.2.
Heartwood (also often called truewood) extends from the
sapwood through towards the centre of the tree. These
cells do not contain any food or starch. Heartwood is
formed from the gradually dying sapwood. It contains
tannins and other materials, making it usually darker and
more durable than sapwood.
Introduction
Figure 2.2: Section across a tree trunk, showing
its structure
Softwoods and Hardwoods
Introduction
Timbers are divided into two groups:
Softwoods or non-pored timbers
Hardwoods or pored timbers.
Non-pored (softwoods) Oregon, Radiata pine, Canada
pine, Redwood, Western red cedar, Cypress pine,
Queensland pine, Hoop pine, Baltic pine Note: All pines
and firs are softwoods
Pored (hardwoods)
Tallow wood, Brush box, Black butt, Red gum, Spotted
gum, Blue gum, Mountain ash, Stringy bark, Iron bark,
Mixed hardwoods, Silky oak, Silver ash, Queensland
maple, Red cedar, Pacific maple, (Meranti) Black bean,
Blackwood, Ramin,
Note: All eucalypts are hardwoods
Introduction
Soft wood and Hardwood
Study Figure 2.3 and 2.4 detailed illustrations of the
Structure of Softwood and Hardwood contained in
the guide.
The composition of wood
The chemical composition of wood is very complex. The
main constituents are:
Cellulose
Lignin.
Other substances are also present. One such group is
the extractives.
Introduction
Cellulose
Cellulose is a complex carbohydrate that makes up the
cell walls in plant tissue, it is what gives wood its tensile
strength. Cellulose is the main component of pulp and
paper.
Lignin
Lignin binds wood fibres together, giving wood its
structural strength. It is plastic when hot, which is why
heated or steam-treated timber is much easier to bend.
Introduction
Extractives
Extractives are substances in wood that can be
extracted by being dissolved in solvents. They include
sugars and starches in the sap, oils and resins (which
give many woods their characteristic smells) and
tannins.
Resins are present in many pines, in Douglas fir and
Oregon. A high concentration of resins can greatly
increase the durability of some woods in two ways:
less moisture absorbent
Deters invading organisms.
Answer the questions in your guide
Resins
Introduction
Because they flow when heated, resins may exude as
sticky drops through surface coatings of stains, paints and
other treatments.
Kiln drying of such woods reduces this risk.
Similarly, rose mahogany and northern silky oak
sometimes exude gums which have a harmful effect on
finishes, and where it is necessary to apply surface
finishes, these timbers should, if affected, be avoided.
Tannins are present in all woods, although some trees
contain quite a lot more tannin than the average. When
tannin comes into contact with metal, the timber will stain
(for fuller details see the section later in this unit on stains
in wood).
Complete the questions in the guide
Conversion into timber
Introduction
Sawing methods
There are two main sawing methods:
live sawing
Sawing around.
Live sawing
Live sawing is the simplest way of sawing a log and
involves sawing through and through (see Figure 2.5 in
your guide), using large circular saws (band saws).
Live sawing is well suited to fast, large-scale production
from small logs of good form with few defects.
Can result in a large number of seasoning faults (warps,
twists, cupping etc).
Figure 2.5: Cross-section through ‘live sawn’ log
Introduction
Figure 2.5: Cross-section through ‘live sawn’ log
Introduction
Sawing around
Sawing around
Involves turning the log during the sawing process so
that a number of different cutting directions are
obtained. The most common method of sawing around
used in Australia is back sawing (see Figure 2.6), but
quarter sawing is also used.
Back sawing
Back sawing takes longer than live sawing but is more
flexible and enables high grade timber to be produced
from faulty logs.
Figure 2.6: Examples of back sawn and quarter sawn
logs
Introduction
Figure 2.6: Examples of back sawn and quarter sawn logs
Introduction
Quarter sawing
Quarter sawing is the only sawing method that reveals
the decorative features in some figured timbers (eg
Queensland walnut and maple). Some coarse-textured
timbers give a harder wearing board when quarter sawn
as it reduces the effect of detrimental gum veins in some
eucalypts, and quarter sawn timber dries more slowly and
is less likely to develop defects and distortions in
seasoning.
Introduction
Seasoning
Seasoning is a process of drying out the green timber to a
desirable level. This reduces the chance of the timber
shrinking, splitting or deforming when used. Drying makes
the timber lighter, increases its strength and prevents its
deterioration from fungal decay or attack by some insects.
Green, sappy wood will not easily take paints, glues and
stains, and will exude sap and moisture.
Seasoning is carried out by:
stacking the timber and allowing it to dry out naturally in
the air
drying it out more quickly in controlled-heat kilns
a combination of air and kiln seasoning.
The seasoning process has to be controlled to prevent
unacceptable shrinking, splitting or warping and twisting.
Introduction
Stress grading
Timber is stress graded to determine the amount of
bending stress it can safely withstand. This allows
timber to be used safely and efficiently.
There are two methods for stress grading timber:
Mechanical.
Visual grading
Visual grading occurs when experienced graders
inspect timber and grade it by eye.
Introduction
Mechanical grading
Timber is fed into a machine which applies continuous
stress along the length of the timber and then marks it
with spray-on coloured dyes (the colour of the dye
indicating the stress grade). Sometimes one length of
timber will be marked with more than one colour to
indicate changes in its strength. The stress grades and
colours are shown in Table 2.2 (the higher the number,
the greater the stress it can withstand).
Table 2.2: Stress grades and colour codes for timber
Stress grade Colour code, F4red, F5black, F7blue,
F8green, F11purple
Timber sizes
Introduction
Timber is sold as either:
Sawn timber (i.e. as it comes, straight from the saw)
Dressed timber sawn timber that has been machinedressed straight and flat all round.
In most instances standard lengths start at 1800 mm (or 1.8
m) and increase in units of 300 mm up to 6300 mm.
Quantities of timber can, however, be produced to special
lengths to order.
Dressed timber can be specified as the finished size or,
more commonly, as the original sawn size from which it is
dressed. A piece of 100 (75 timber, for example, will measure
several millimetres less on each face when dressed, due to
planing and sanding. The symbol% (or ex) means ‘out of’;
thus % 100 (75 means that the piece is dressed from a sawn
section of 100 (75.
Introduction
Milled (or dressed) timber
Timber that has been machine-finished to a particular
width and thickness or has been machined to a specific
shape is called milled or dressed timber.
Milled timbers include the following:
Square and rectangular sections
Tongue and groove boards
Weatherboards and wall panelling
Mouldings.
Study the sections and mouldings in your guide and
answer the questions
Introduction
Features of wood
Physical characteristics
The appearance of wood is affected by various physical
characteristics:
texture
grain
figure
knots
hardness
wear.
Introduction
Features of wood
Texture
Wood texture is caused by the size and arrangement of the
cells, and by variations in the density of the wood. We
speak of fine, coarse, even or uneven textures.
Grain
Grain refers to the general direction of growth of the wood
tissue, and is shown by the way the fibres separate when
a piece of timber is split. We can have, for example,
straight, spiral, interlock, curly, wavy or cross grain (see
Figure 2.11)
Figure 2.11 Timber showing some types of cross grain
Introduction
Features of wood
Figure
Figure refers to the ornamental patterns seen on the
dressed surface of the timber and is the result of colours
and grain patterns in the wood.
Knots
Knots occur where the branches joined the trunk of the tree.
They are harder and darker in colour than the stem
wood (see Figure 2.12).
Figure 2.12: Timber knots
Introduction
Features of wood
Hardness
Hardness is how well a material resists being dented.
Hardness varies from tree to tree, and also within a tree.
End grain is sometimes harder than side grain, and
sometimes softer.
Figure 2.13 shows a number of timbers, listed in order of
hardness.
Introduction
Features of wood
Iron bark
Grey box
White mahogany
Turpentine
Brush box
Silver top ash
Stringy bark
Karri
Tallow wood
Jarrah
Cypress pine
Radiata pine
Douglas fir (North America)
Red cedar
Hardest
Softest
Introduction
Features of wood
Wear
Some timbers have a greater resistance to wear than others, a
consideration that is particularly relevant to floors.
Generally, hardwoods with a relatively high density, with a
fine, even texture and small pores are most suitable for
industrial or heavy duty floors.
Stains
Some stains occur naturally in wood. Let’s look at some of the
most common types and sources of stains in timber.
Introduction
Features of wood
Surface stains from moulds
Mould stains develop on sawn timber in the early stages of
drying. They do not damage the wood and are removed
when the timber is dressed.
Sap or blue stains
Blue stain fungi may attack the sapwood and heartwood of
both softwoods and hardwoods—plantation pines are
especially susceptible. To stop this, it is important that the
tree is seasoned quickly after felling, especially in the
warmer months. The strength of the timber is not
particularly affected, but the appearance can be streaked
and ugly.
Introduction
Features of wood
Decay discolour
Pockets or streaks of red-brown or whitish wood may indicate
decay. Such wood may be considerably softer than the
surrounding wood. This material is often brittle and will
usually break if you attempt to prise it out with a knife. This
decay is stopped by seasoning and proper maintenance
afterwards.
Stains from metals
When the tannins present in wood come into contact with
metals a chemical reaction takes place, resulting in the
timber becoming stained; for example, the blue-black stain
that occurs from contact with iron and steel.
Introduction
Features of wood
Staining occurs more easily with green (unseasoned) wood, but
if seasoned timber is wet it can still stain. For this reason,
external fittings and fasteners should either be galvanised
or else not made from metals containing iron or steel.
Iron or steel will, however, cause little or no staining on the
following species:
Blackwood, brown alder, brush mahogany, camphorwood, silver
quandong, yellow wood.
Copper nails can cause a slight reddish brown stain on some
timbers. Aluminium, and galvanised iron and steel do not
cause staining, but it is important that the zinc coat on the
head of galvanised nails isn’t damaged.
Introduction
Features of wood
Chemical changes within the wood
As the tree grows it can naturally produce colour variations of its
own which show up as streaks or blotches. These often
increase the decorative value of the timber.
Introduction
Features of wood
Stains due to leaching
Intermittent wetting and drying of an uncoated piece of
timber can result in colours in the timber migrating, resulting
in stains. These can also be carried in the water onto
nearby paintwork, brick or concrete, causing unsightly
marks. They will eventually fade, or they can be removed
with dilute acids such as citric or oxalic acid in a 10%
solution in hot water.
Species susceptible to such staining include Blackbean,
NSW walnut and all eucalypts. Softwoods and most
rainforest species are seldom affected.
Introduction
Features of wood
Defects in timber
Defects in timber can affect both its appearance and
strength. These defects may occur as the wood grows,
when the wood is processed or as a result of weathering.
The degree of loss of strength is taken into account when
the timber is graded.
The appearance is not usually important with structural
timbers, but very relevant with wood used for finished
surfaces and veneers, for example.
Introduction
Features of wood
Defects resulting from the growth process
Generally, defects which result from the growth of the tree are:
sloping grain
knots
gum pockets and veins
reaction wood
pith
cone holes.
Introduction
Features of wood
Sloping grain
Figure 2.14: Sloping grain
Knots
Knots can add to the attractiveness of decorative timbers,
but affect the strength of structural timbers.
Gum pockets and veins
Cavities in the wood become filled with resin (in softwoods)
or gum (in hardwoods). These gum pockets and veins do
not usually affect strength but can often affect appearance.
Reaction wood
Reaction wood is growth that occurs in a tree that is trying
to compensate for a lean or bend for example.
Introduction
Features of wood
Pith
Pith is a soft, furry brown zone, occurring during early tree
growth. It is weak and unattractive, and is found especially
in young softwoods.
Cone holes
These are holes that form from the pine cone remaining
attached to the tree trunk, and the stem of the cone falling
when the wood is sawn.
Introduction
Features of wood
Defects that occur during felling, seasoning or other
conversion processes
Checks
During surface drying, a separation of the layers of wood
extending along the grain may occur. These separations
are called checks.
Figure 2.17: Checks in timber
Splits
Splits are cracks that extend from one surface to another at
the end of a piece of timber.
Introduction
Features of wood
Shakes
Shakes are areas of complete or partial separation between
layers caused by processes other than drying; by felling, for
example.
Figure 2.19: Examples of shakes
Distortion
Growth stresses within the live tree, and stresses during the
sawing, drying or storage of timber can result in distortion,
or warping, as it is often called (see Figure 2.20).
Introduction
Features of wood
Weathering
Weathering results from the combined effects of sunlight
and rain. At first, the dark colours fade and light colours
darken, but in time all weather-exposed timbers turn grey.
This surface grey colour sometimes gets dirty and blotchy
because of fungal organisms, but in dry climates or coastal
areas of salt spray a lovely silver grey often develops, as is
often seen on driftwood.
Weathering also causes the grain to stand out and the
surface to gradually break down. This surface decay can be
quite rapid if dampness is present and rot develops.
Introduction
Timber destroying agents
Wood-inhabiting micro-organisms
These micro-organisms include surface moulds, blue stain
fungi, fungi causing wet and dry rot and bacteria. Some (eg
blue stain) mar the appearance but not the strength,
whereas the fungal rots can completely destroy affected
timbers, reducing them to soft, spongy material with no
strength.
Introduction
Insect attack
Termites
Often misnamed ‘white ants’, termites prefer moist, dark
conditions and are extremely destructive to timber. They eat
out the inside of wood, along the grain, leaving only a thin
shell of wood.
This destruction can be avoided by using termite-resistant
timbers, and by isolating timber from the ground, through
which termites travel. Efficient chemical termite barriers may
also be used to prevent their access. Various poisons are
used either to spray affected soils and timbers, or directly on
the soil as a barrier to potential invasion or to treat wood
before use; however, as many of these chemicals are highly
toxic, extreme care should be taken
Introduction
Insect attack
Powder post beetle (Lyctus)
This wood-boring beetle infests cut timber. It lives off the
starch in the sapwood of pored (hardwood) timbers and,
although confined to sapwood, can cause considerable
damage. In NSW, before being marketed, most susceptible
timbers are required to be treated with a preservative that is
toxic to this beetle.
Furniture beetle (Anobium)
This borer, which also lives off starches in the wood, chiefly
infests the sapwood of seasoned softwoods and can cause
extensive damage in untreated wood. The tunnels that are
bored out form a honeycomb appearance in the timber,
leaving a deposit of fine gritty dust. Affected timber should
be treated or removed and destroyed, to prevent spread.
Introduction
Insect attack
Pinhole beetle (Ambrosia)
These beetles attack almost any tree species but only the
green timber. The beetle is killed off as the timber dries out
with seasoning. Various chemicals are used to prevent or
destroy infestation.
Fire damage
Fire causes serious and spectacular damage to timber
because of timber’s flammability. While the fire hazard of
timber construction is often greatly exaggerated, the fact
remains that timber is the only primary structural material
that will ignite and burn at high fire temperatures.
Attempts are being made to deal with this problem by
developing fire-retarding treatments.
Introduction
Timber preservation
Some timbers are naturally durable. Durability can be
affected by the chemical make-up of the timber itself, its
hardness and the amount of sapwood present in the
sample.
For instance, timber with a high concentration of phenolic
compounds may be extremely durable, whereas timber with
a high carbohydrate content (eg radiata pine) is extremely
susceptible to fungal attack. Termites, on the other hand,
are less affected by phenolic compounds than by the
hardness of the timber. Brush box and turpentine, for
example, have high levels of silica compounds which make
them difficult for the termites to chew.
Introduction
Timber preservation
The amount of sapwood present can reduce the durability
of the timber as a whole. The sapwood of most tree species
is susceptible to decay and insect attacks, whereas the
heartwood of most Australian species is quite durable.
Timbers can be placed into one of four classes for
durability; class 1 being the most durable when in contact
with the ground. Examples of common timbers in each of
the four classes are shown in Table 2.3.
Introduction
Table 2.3: Timber durability classes
Class 1iron barks, grey gum, grey box, cedar, tallow wood,
junipers, turpentine, red wood.
Class 2 black butt, spotted gum, forest red, gum white, stringy
bark
Class 3 brush box, (class 1 or 2 for termites) brown stringy
bark, silvertop ash.
Class 4 yellow carabeen radiata pine white birch douglas firs
sassafras hemlocks tulip oak spruces slash pine beeches
birches
Introduction
Timber preservation
Timber which is not naturally durable may be impregnated
with preservatives to improve its durability. Preventative
treatment of timber before sale and use is most effective.
Commercial or large-scale treatments available in Australia
fall into one of four main categories:
oil-based preservatives
waterborne preservatives
– unfixed salts
– fixed salts
organic solvents or light oil solvent preservatives
(LOSPs).
Introduction
Timber preservation Oil-based preservatives
The most commonly used oil-based preservative is
creosote, a dark brown distillate of coal tar. It is widely used
to protect fence posts, transmission line poles and railway
sleepers, and can be applied commercially by pressure
impregnation or by on-site soaking or brushing. It provides
protection against insect attack and decay but has an
offensive odour, blackens the timber, and timber so treated
cannot be painted or finished. Creosote is also a harmful
substance and should not be inhaled or absorbed through
the skin.
Introduction
Timber preservation
Waterborne preservatives
Unfixed salts
The waterborne preservatives involving unfixed salts
include borax, boric acid and sodium fluoride. These must
be diffused or forced commercially throughout the sapwood
of susceptible timber and plywood. These preservatives are
odourless and non-staining but are not permanent where
timber is exposed to water. This treatment is aimed at
control of Lyctus (powder post borer).
Introduction
Timber preservationFixed salts
The major waterborne preservative involving fixed salts
currently in use in Australia is copper chrome arsenic
(CCA). The timber is usually pressure treated and the active
components deposited within the timber are permanent.
Timber so treated develops a slight green colour and is
protected from borers, termites and decay, even for inground applications. After treatment, it is odourless and can
be easily painted.
Introduction
Timber preservationFixed salts
CCA compounds are heavy duty preservatives which are
not susceptible to leaching. The copper is a fungicide and
the arsenic is an insecticide and also limits fungal growth.
The chrome acts as a fixing agent, making the copper and
arsenic chemicals insoluble.
Introduction
Timber preservationOrganic solvents
The use of organic solvents or light oil solvent
preservatives (LOSPs)
pressure treatment in which active chemicals are dissolved in
clear organic solvents and forced into the timber. A variety of
chemicals may be used, which could include
pentachlorophenol aldrin, dieldrin, tributyltinoxide and water
repellents (waxes) depending on the level of protection
required. Timber so treated can be used in exposed
situations above ground and, as the original colour of the
timber is unchanged, it is suitable for exposed decorative
finishes.
(For more detailed information, refer to Timber Development
Association, TDA Technical Notes TN81/01 ‘Timber
Preservation’.)
Introduction
Manufactured boards
A number of different types of manufactured boards are
produced for a variety of uses with some advantages over
regular timber, and include plywood, particle board,
hardboard, solid core board, composite sheet, laminated
sections and medium density fibreboard.
Introduction
Manufactured boards
Advantages of manufactured boards
Strength is greatly increased and is more uniform. Solid
wood is, on average, 20 times stronger along the grain than
across. Thick plywood (over 10 mm thick), on the other hand,
is almost equally strong in both directions.
Shrinkage is practically eliminated.
Boards are available in much larger sizes than can be
obtained from a tree trunk.
Introduction
Manufactured boards
Advantages of manufactured boards
More economical use can be made of expensive timbers for
finishes, while cheaper timbers can be used for the cores.
Matching uniform panels can be obtained.
Plywood can be formed or bent to make curved surfaces.
Fewer splitting problems occur when nailing or screwing.
In the case of composite boards, much greater strength-toweight ratios are obtained and they also have improved
insulating qualities.
Boards are made to very accurate measurements.
Introduction
Manufactured Plywood
Thick continuous sheets are peeled off rotating logs of
wood and then glued together in layers, under pressure.
Each layer is laid at right angles to the grain direction of the
previous layer (see Figure 2.21), and there is always an
odd number of layers. Plywoods are often named according
to the number of layers (eg three-ply, five-ply and so on).
Decorative timber surfaces on sheets provide attractive
finishes for cabinet making, wall panels or wherever a
timber finish may be required.
Introduction
Manufactured Plywood
Properties
Plywood has very good strength for its weight and is very
resistant to shear stress. Thin sheets can be readily bent to
required curved shapes. Glues and coatings can, when
needed, make plywoods moisture resistant so that they can
survive weather, wet concrete and marine conditions.
Uses
Its wide range of uses includes sheet flooring, external and
internal wall cladding, sheet roofing underneath other
roofing materials, components for structural members,
formwork for concrete, decorative panelling fixtures,
furniture and wall bracing.
Introduction
Manufactured Plywood
Properties
Standard sheet sizes (for residential construction) are:
standard length: 2400, 2100, 1800 mm
standard width: 1200, 900 mm.
Other sizes are manufactured for special uses.
Introduction
Particle board
Also called chipboard, this board is made from wood chips
glued together under pressure to form solid sheets.
Properties
Particle board has good dimensional stability, and is easy to
work with normal carpentry tools, making it ideal for cabinet
work. It does not have the same bending and shear
strengths as most other timbers and prolonged exposure to
moisture will make it swell, causing a reduction in strength
and hardness.
Uses
Introduction
Particle board is used for tongue and grooved sheets for
flooring (both sheets are grooved and a plastic tongue fits
into each groove); plain sheets for internal fittings and
cabinet making; plain sheets surfaced with formica for
tables, bench tops, cupboard sides and doors. Sheets are
also made in widths suitable for shelving and edge-stripped
with timber along one edge to enhance their appearance.
Standard sizes are:
thickness: ranges from 10–43 mm
width: 600–1800 mm
length: 1800–4800 mm
Note: Standard sizes for particle board flooring are:
thickness: 19 mm
width: 600 and 900 mm.
Hardboard (masonite)
Introduction
Wood is pulped and a felt of wood fibres, impregnated with
glues, is compressed and cut into sheets of hardboard, also
commonly called masonite. The sheets are rough on one side
and hard and smooth on the other (unless a decorative texture
is pressed into them).
Types
Hardboards fall into several groups:
natural-colour hardboards
prime-coated hardboards (ie natural colour hardboards which
have been factory primed with pigmented paint sealers)
perforated hardboards (with a regular pattern of holes
punched in them and used for ‘peg’ boards, notice boards and
sound insulation)
pre-finished hardboards (with a variety of finishes and
textures).
Introduction
Uses
Hardboards are extensively used in the building industry. Uses
include: as wall and ceiling linings; as underlay, to provide an
even surface for cork or vinyl titles or sheets; in cabinet making;
as facing panels on doors; for decorative feature walls; for
partitions and wall bracing.
Introduction
Solid core board (coreboard)
This is made up of a number of solid strips of timber glued
together and sandwiched between sheets of cross bonding and
face veneering (see Figure 2.23).
Figure 2.23: Coreboard
Composite sheet
Also known as sandwich ply, this has an inner core of insulating
material, sheathed with plywood (see Figure 2.24).
Introduction
Solid core board (coreboard)
This is made up of a number of solid strips of timber glued
together and sandwiched between sheets of cross bonding and
face veneering (see Figure 2.23).
Figure 2.23: Coreboard
Composite sheet
Also known as sandwich ply, this has an inner core of insulating
material, sheathed with plywood (see Figure 2.24).
Advantages of glued laminated components
Introduction
Strength characteristics can be carefully controlled throughout
the length of the beam and, depending on the types of timber
used, glued laminated beams can be obtained in stress
gradings ranging from F8 to F27.
Large structural members can be made from readily available
commercial sizes of seasoned timber.
The member so formed will be more dimensionally stable and
free of surface checks and so on, than the necessarily
unseasoned single piece of solid timber.
Design and fixings can be based on the properties of seasoned
timber.
Material of lower grade can be positioned in the made-up
member in locations where it will not affect the overall strength
of the member.
Introduction
Structural members with curved, tapered or cambered shapes
can be produced readily. Timbers approximately 25–37 mm
thick are usually selected, dressed smooth and then placed
together with adjacent faces glued and pressed. In this process,
the section can be bent to follow desired forms and the resulting
shaped components have great stability and structural strength.
They have a good degree of fire resistance because the surface
usually chars then resists further burning. They are also useful
in corrosive industrial atmospheres.
They have a pleasing appearance which has been a great asset
in high-quality work, such as public building interiors.
Introduction
Medium density fibreboard
Medium density fibreboard is made of timber chips or fibres
which are compressed with glues to form smooth, even-textured
boards which are easily worked and stable. They are ideal for
cabinet work and their superior finish has made them a viable
alternative to timber for domestic mouldings.
Introduction
Health and safety
A number of timbers contain extractives that can be extremely
irritating to skin and mucous tissue, especially when in fine
sawdust. Timbers known to contain irritant compounds include
crows ash, black bean, silky beech, black wood, western red
cedar, miva mahogany, silky oak, cypress-pine, makore and
guarea (both imports from Africa).
As a general health and safety consideration, prolonged
exposure to dust, both natural and manufactured, is known to
cause disease and every precaution, including dust extraction,
dust masks and personal cleanliness must be observed.
Answer the questions in your guide