Over Five Decades of Service to the Plywood Industry
The CertiWoodTM Technical Centre (formerly named the Canadian Plywood Association or CANPLY) is a non-profit,
industry-funded association representing manufacturers of engineered wood products in Canada. Since the association’s
name change in 2005 from CANPLY to CertiWoodTM, plywood producing companies have retained the CANPLY trademark and
continue to stamp their production with the well-known mark. The CANPLY stamp continues to serve as an assurance to
buyers that the plywood is produced under CertiWood’s exacting 3rd party quality auditing process and that it will perform in
a satisfactory and predictable manner.
CANPLY plywood is manufactured by 6 companies belonging to CertiWoodTM (member companies) operating in British
Columbia and Alberta. Together, these companies operate 9 mills and produce over 90% of all structural, construction and
industrial plywood manufactured in Canada. Member company plywood production is about 1.7 billion square feet (3/8" basis)
annually. Approximately 90% is shipped to markets across Canada. The balance is exported to some 28 countries, among
these: the United States, Japan, the United kingdom and Germany.
Originally founded in 1950, CertiWood™ has a long history of service to its member companies and their customers. Today,
CertiWood’s purpose is, “To provide cost-effective certification, quality auditing and testing services to Canadian engineered
wood products manufacturers”.
CERTIFICATION MARkS
The registered certification marks shown below appear on CANPLY EXTERIOR Douglas Fir plywood (DFP),
CANPLY EXTERIOR Canadian Softwood plywood (CSP) and CANPLY EXTERIOR Poplar Plywood manufactured by our
members to meet the requirements of CSA O121, CSA O151 or CSA O153. CertiWood™ also certifies its Members’ products
to meet US and other international standards (see below).
Face Stamp on CANPLY EXTERIOR Plywood (Unsanded grades)
www.canply.org
Licensed mill number of the CertiWood™ member
Indicates that this product is manufactured under CertiWood’s
Quality Certification Program.
Indicates that the plywood has been manufactured by a member of CertiWood™
Indicates a completely waterproof glue bond
Indicates species designation: DFP (Douglas Fir plywood),
CSP (Canadian Softwood plywood), Aspen or Poplar plywood
Indicates the CSA standard governing manufacture
Edge Stamp on CANPLY EXTERIOR Plywood (Sanded and Unsanded grades)
Indicates that the plywood has been manufactured by a CertiWood™ member and is
quality certified
Indicates a completely waterproof glue bond
PLYCO CANADA BC xxx CANPLY EXTERIOR CSP GRADE
Panel grade
Indicates species designation: DFP (Douglas Fir plywood),
CSP (Canadian Softwood plywood), Aspen or Poplar plywood
Licensed mill number of CertiWood™member (BC xxx, AB xxx).
This symbol identifies the patented tongue and groove profiles of CANPLY T&G
products formerly known as COFI FLOOR & COFI ROOF.
Face stamp on COFI FORM Douglas Fir plywood for concrete formwork.
INTERNATIONAL CERTIFICATION MARkS:
Japan
uSa
certiWood™ Canply plywood Handbook
2
EuropEan union
Panel Construction
Plywood
Handbook
CANPLY EXTERIOR plywood is an
engineered panel built up from sheets of
veneer glued together with a waterproof
resin adhesive.
The thickness and
orientation of the plies determine the
performance of the panel. The veneers are
united under high temperature and pressure
with a resin glue that is completely
waterproof, making the plywood suitable for
use under conditions of extreme exposure to
moisture.
Species
Plywood marked CANPLY EXTERIOR may be
designated as Douglas Fir (DFP), Canadian
Softwood (CSP), Aspen or Poplar plywood.
CANPLY EXTERIOR PLYWOOD
Information in this brochure pertains to
CANPLY EXTERIOR Douglas Fir plywood,
CANPLY EXTERIOR Canadian Softwood
plywood and CANPLY EXTERIOR Poplar
plywood. These products are manufactured
in accordance with Canadian Standards
Association Specifications CSA O121
Douglas Fir Plywood, CSA O151
Canadian
Softwood
Plywood
or
CSA O153 Poplar Plywood by companies
who are members of CertiWood™. CANPLY
certification stamps, shown opposite, are on
all Canadian Plywood products meeting
CertiWood™’s Quality Certification Program.
Contents
page
CANPLY EXTERIOR Plywood ....................3
Plywood Grades and Products .................6
Sizes and Thicknesses .............................6
Working with Plywood ...............................8
Fasteners ...................................................8
Glues and Gluing ...................................10
Floor Sheathing .......................................11
Wall Sheathing ........................................14
Roof Sheathing .......................................18
Permanent Wood Foundations ...............19
Concrete Forms .......................................19
Plywood in Farm Structures ....................23
Plywood Structural Assemblies ..............23
Finishing ..................................................23
Preservative Treatments ..........................26
Fire Retardant Treatments .......................26
Specifying Plywood .................................27
CANPLY EXTERIOR Douglas Fir plywood is
manufactured with faces of Douglas Fir
veneers. The inner plies and some backs
may be of veneers of the selected
coniferous species shown in Table 1. The
permissible species for CANPLY EXTERIOR
Canadian Softwood plywood are also
shown in Table 1. For a complete list of
allowable species in CANPLY Poplar
plywood, please refer to the standard CSA
O153.
Manufacture
The manufacturing process begins by
conveying selected logs to a barker where
they are rotated against a steel claw to strip
the bark and debris from the log surface.
The logs are then cut into peeler blocks. In
conformance with today’s standards of
sustainable forestry, the logs we harvest are
from secondary growth forests and average
25cm (10") in diameter.
After conditioning, peeler blocks are moved
to a lathe where they are set in the chucks by
an automatic charger. Using laser sensors,
the block is imaged and automatically
aligned in the lathe to maximize veneer
recovery. As the block is rotated, the honed
steel blade of the lathe is brought in contact
with it, peeling a continuous sheet of veneer.
As veneer is produced it is directed to
semiautomatic clippers that scan the veneer,
remove oversize defects and cut it to width
for sorting and stacking. Standard widths
are stacked automatically and random
widths manually. Veneer is passed through
moisture sensors and segregated by
moisture content. Segregation is necessary
as veneer with different moisture contents
requires different drying cycles.
Veneer is dried in steam or gas-heated
ovens at temperatures ranging from 160 to
200 °C. The speed at which the veneer
moves through the dryer depends on the
thickness of the veneer and its moisture
content.
3
After passing through the dryer, electronic
moisture detectors mark all veneer in excess
of the moisture content allowed for gluing.
The veneer is stacked separately and later
re-dried.
After dying, the veneer is optically scanned,
imaged on a computer and further sorted
according to grade. Narrow widths may be
directed through a composer where edges
are cleaned, squared and “welded” into
continuous sheets and clipped into standard
widths.
Substandard
veneer
with
oversize
imperfections is either discarded or
channeled to patching machines where the
imperfections are neatly replaced with
sound wooden patches.
Sound veneer then moves to the glue
spreader or automatic lay up line where the
veneers are uniformly coated with resin glue
and laid at right angles to the adjacent
veneers. This cross-lamination accounts for
plywood’s exceptional two-way strength and
dimensional stability.
After lay up, the veneer sandwiches go to
the hot press, the key operation in the
manufacturing process. Here, depending
upon the thickness of the plywood panel,
one or more sandwiches are loaded into
each press opening. The press is then
hydraulically closed and the panels
subjected to a temperature of 150 °C and a
pressure of 1.38 MPa which cures the glue.
The resin glue, when cured in the hot press,
produces an inert water-proof bond.
After removal from the hot press, trim saws
cut the plywood panels to the required
dimensions, usually 1220 mm by 2440 mm
(4' x 8'). Panel edges and panel ends are
trimmed in consecutive operations.
Panels are then graded as sheathing or
selected for further finishing. Panels to be
produced as sanded grades pass to a
sander where face and back are
simultaneously sanded smooth.
Any minor imperfections remaining in the
face and back veneers may be repaired with
wood inlays or synthetic filler before the
panels are finally graded by skilled
inspectors.
All grades of plywood produced by
CertiWood™ members are then stamped
with the registered certification mark
CANPLY EXTERIOR before leaving the mill.
Most wood waste during manufacture is
collected and burned in high efficiency
burners to be converted into heat or
electricity, offsetting most of the mill's energy
needs.
certiWood™ Canply plywood Handbook
Table 1. Species permitted in Canply Exterior plywood
* Permitted on the backs of 6, 8, 11 and 14 mm Good One Side DFP
** Not permitted in sheathing grades
Steps in the manufacture of plywood
1. The log emerges from the barker after having
been stripped.
2. Logs are conditioned using steam or hot water
to improve peel quality
3. At the lathe, a sharp blade peels the log, now
called a block, into a continuous sheet of veneer.
certiWood™ Canply plywood Handbook
4
4. Green veneer is dried in steam or gas
heated ovens.
5. Veneers are coated with waterproof glue
and laid up into sandwiches.
6. The veneer sandwiches are subjected to
heat and pressure in the hot press until
the glue is cured.
7. After pressing, the panels are trimmed,
squared, and selected for grade.
8. Finished panels are carefully inspected
and graded.
9. CertiwoodTM quality control inspectors
check finished panels in inventory.
11. Other samples are subjected to the boiling
test specified by the CSA.
12. Some samples are subjected to vacuumpressure tests.
10. Plywood samples, selected at random,
are tested at the CertiWood™ Technical
Centre.
14. Panels that meet our stringent
requirements are identified with the CertiWood™
Certification Mark.
13. Samples are shear tested to determine the strength of the glue bond.
5
certiWood™ Canply plywood Handbook
PLYWOOD GRADES AND PRODUCTS
Tongue and Groove Plywood
CertiWood™ members produce a wide
range of CANPLY EXTERIOR plywood
grades and products. Grade names in
general are based on the quality of the
veneers used for the face and back of the
panel. CANPLY EXTERIOR plywood grades
are shown in Table 3. A list of proprietary
CANPLY Exterior Plywood products is given
in Table 4.
T&G plywood has a factory-machined
tongue along one of the long edges and a
groove along the other. T&G panels
interlock to ensure the effective transmission
of loads across joints, eliminating differential
deflection between adjoining panel edges
and making the use of blocking or H-clips at
longitudinal joints unnecessary.
Overlaid Plywood
Plywood is also manufactured with overlays
which improve the appearance and
durability of the panel. The overlays are
bonded to the face veneers of the plywood
by heat and pressure. This process seals
the overlay to the wood to form an
inseparable bond stronger than the wood
itself. The resin content of the overlay
determines whether the final product is
called Medium or High Density Overlaid
plywood.
panels designed specifically for use as
concrete formwork. These panels are
significantly
stiffer
than
standard
construction of DFP in wet service
conditions because of stricter limits on
species and ply thicknesses during
manufacture. COFI FORM PLUS is the
stiffest Douglas Fir panel manufactured by
CertiWood™ members (Table 4).
SIZES AND THICKNESSES
CertiWood™ members manufacture two
patented T&G panels, under one name –
EASY T&G. These panels have T&G edges
specifically designed for roof and floor
sheathing. Panel installation is fast and easy
with these patented edge profiles, exclusive
to CertiWood™ members
CANPLY EXTERIOR plywood is manufactured
in a size of 1220 mm by 2440 mm, the metric
equivalent of the familiar 4 ft by 8 ft panel. It
is also available in a metric size of 1200 mm
by 2400 mm (Table 2). Net face widths for
EASY T&G are given in Table 2.
Concrete Form Panels
CANPLY EXTERIOR plywood is manufactured
in a range of thicknesses from 6 mm to over
30 mm as shown in Table 2.
All plywood bearing the registered
certification mark CANPLY EXTERIOR is
suitable for concrete formwork because it is
manufactured with waterproof glue.
NOTE: CANPLY EXTERIOR plywood panels
are available in additional sizes and
thicknesses on special order.
CANPLY EXTERIOR DFP is
Medium Density
available in sanded and
The
resin
unsanded grades and in special
impregnated
high strength constructions.
face presents a
CANPLY EXTERIOR CSP is
smooth uniform
available in unsanded grades
surface intended
only. Sanded grades produce a
for high quality
smooth, wood grain finish valued
paint
finishes.
by many architects. Unsanded
Some evidence
grades are suitable for formwork
of the underlying
EaSy T&G - Floor profile
where the appearance of the
grain
may
concrete is less important such as in subappear. Overlay is produced in a natural
surface foundations.
buff colour and certain other colours.
Popular uses for Medium Density Overlaid
plywood are flat, lap and bevel sidings; and
sundecks, soffits and accent panels in
residential construction. Other applications
include boats, highway signs and many
other commercial uses.
High Density
The resin impregnated face is hard, smooth,
and chemically resistant. No further finishing
with paint or varnish is necessary. The
overlay is usually produced in a whitish
semi-opaque colour but other colours may
be used by manufacturers for identification.
Major uses for High Density Overlaid
plywood include fine finish concrete
formwork, storage bins, liquid tanks and
signs.
Mill Specialties
Mill specialties are variations of the plywood
grades and products shown in Tables 3 and
4. These panels are manufactured by a
number of member companies and
marketed under their own brand names. Mill
specialities include patterned, overlaid,
textured, brushed, embossed, striated,
grooved and pre-finished panels for
decorative use.
certiWood™ Canply plywood Handbook
CANPLY EXTERIOR plywood is also
available edge sealed, treated with chemical
release agents, and with resin impregnated
cellulose fibre overlays. Overlays produce
the highest quality concrete finish. They also
help protect the plywood from oil and water,
simplify form stripping and extend the
service life of concrete forms.
COFI FORM PLUS and COFI FORM are
special high-strength constructions of DFP
EaSy T&G - Roof profile
Table 2. Sizes and Thicknesses of Canply EXTERIOR plywood
Thickness
Sheathing and
Select Grades
Sanded Grades
6 mm
8 mm
11 mm
14 mm
17 mm†
19
21
24
27
30
Size
mm†
mm†
mm†
mm†
mm†
7.5 mm
9.5 mm
11 mm†
12.5 mm†
15.5 mm†
18.5 mm†
20.5
22.5
25.5
28.5
31.5
mm†
mm†
mm†
mm†
mm†
All thicknesses are metric, but some approximate
imperial dimensions, e.g. 6 mm (1/4 in.)
† Available as square edge or with
EASy T&G edge.
6
Lengths
Available up to 2500 mm
W i dt h s
Available from 600 mm to 1250 mm
For EASy T&G panels, deduct 15
mm from the nominal width for net
face coverage.
Table 3. CANPLY EXTERIOR Plywood Grades
Veneer Grades**
Grade*
Product**
Good Two Sides
DFP
(G2S)
Characteristics
Inner
Plies
Back
A
C
A
Sanded. Best appearance both faces.
May contain neat wood patches, inlays
or synthetic patching material.
Furniture, cabinet doors, partitions,
shelving, concrete forms and opaque
paint finishes
Sanded. Best appearance one side
only. May contain neat wood patches,
inlays or synthetic patching material.
Where appearance or smooth sanded
surface of one face is important.
Cabinets, shelving, concrete forms.
Sanded
Poplar
Good One Side
(G1S)
DFP
A
C
C
Select Tight Face
(SEL TF)
DFP
B***
C
C
Select
(SEL)
DFP
Aspen
Poplar
CSP
Sheathing
(SHG)
DFP
Aspen
Poplar
CSP
High Density
Overlaid (HDO)
DFP
Aspen
Poplar
CSP
Medium Density
Overlaid (MDO)
MDO 1 Side
MDO 2 Sides
DFP
Aspen
Poplar
CSP
DFP
Aspen
Poplar
Typical Applications
Face
Surface openings shall be filled and
may be lightly sanded.
Underlayment and combined subfloor
and underlayment. Hoarding.
Construction use where sanded
material is not required.
B
C
C
Surface openings may be filled and
may be lightly sanded.
C
C
C
Unsanded. Face may contain limited
size knots, knotholes and other minor
defects.
Roof, wall and floor sheathing.
Hoarding. Packaging. Construction
use where sanded material is not
required.
B***
C
B***
Smooth, resin-fibre overlaid surface.
Further finishing not required
Bins, tanks, boats, furniture, signs,
displays, forms for architectural
concrete.
C***
C
C
Smooth, resin-fibre overlaid surface.
Best paint base.
C***
C
Siding, soffits, paneling, built-in
fitments, signs, any use requiring a
superior paint surface.
C***
CSP
Table 4. CANPLY Exterior Plywood Proprietary Products
Product*
Product
Standard**
EASY T&G
ROOF
DFP
CSP
EASY T&G
FLOOR
DFP
CSP
Aspen
Poplar
COFI FORM
PLUS
and
COFI FORM
DFP
(limits on
thickness
and
species of
face and
inner plies)
Grades**
Characteristics
SHG
or
SEL
Milled with patented edge profile for easy
installation and edge support without H-clips
Roof sheathing and decking for
residential, commercial and industrial
construction.
Milled with a patented edge profile for fast,
easy installation.
Floor and heavy roof sheathing for
residential, commercial and industrial
construction.
SHG
SEL
SEL TF
SEL
G1S
G2S
SPECIALTY
HDO
MDO
Special construction Douglas Fir panels
with greater stiffness and strength providing
improved properties particularly in wet
service conditions. Available in regular
sanded and unsanded grades and speciality
grades with resin-fibre overlays. Also
available with factory-applied release agent.
Typical Applications
Concrete forms and other uses where
wet service conditions or superior
strength requirements are encountered.
* All grades and products including overlays bonded with waterproof resin glue.
** For complete veneer and panel grade descriptions see CSA O121 (DFP), CSA O151 (CSP) and CSA O153 (Poplar).
*** Indicates all openings are filled.
7
certiWood™ Canply plywood Handbook
WORKING WITH PLYWOOD
Storing and Handling
Plywood, like any other panel product,
requires proper handling and storage.
Despite its sturdy cross-laminated
construction, face veneers, panel edges and
panel corners are vulnerable to damage
and should always be protected.
Plywood is manufactured at a low moisture
content and while small changes in moisture
content will not appreciably affect its
dimensions, large changes should be
avoided since they may encourage
checking of the face veneer with consequent
impairment of its qualities as a paint base. It
is good practice to store plywood which is to
be used for interior finish under conditions
that approximate those it will experience in
service.
Points to watch when handling plywood are:
1. Store plywood panels flat and level.
2. keep finish faces inward and cover
stacks to protect from bumping and
abrasion.
3. Protect panel edges and corners.
This is especially important with
tongue and groove plywood.
4. Carry panels on edge (always being
careful not to damage faces, edges
and corners).
5. When plywood is used as a finishing
material, deliver to job-site at the last
possible moment.
6. Protect panels from sunlight, water or
excessive humidity.
Sawing
Hand sawing
For handsaw work, panels should be sawn
face (good side) up with the angle between
saw teeth and panel surface as flat as
possible.
This prevents face veneer
splintering. Generally, an 8 or 10 point
cross-cut saw or a 10 point panel saw gives
the best results.
Hand Power sawing
A sharp carbide tip combination blade set to
protrude no more than 12.5 mm through the
panel and firm panel support will give
excellent results with a hand power saw.
Panels should be sawn face down.
Table Power sawing
Panels kept face up on a table power saw
are cut cleaner. A combination blade filed
with less than normal hook is best for most
work. The blade should be set to protrude
no more than 12.5 mm. In general, a blade
of 250 mm diameter or more works best. A
table extension will help in handling full sized
panels. When using a radial arm saw, the
orientation of the plywood panel will depend
on the type of cuts being made. The
certiWood™ Canply plywood Handbook
instruction manual accompanying the radial
arm saw should be consulted.
Planes used on plywood edges are working
on grain that goes in both directions
because of cross lamination of the plies. For
this reason a sharp plane with shallow set is
recommended. A light jack plane will work
well on most jobs and planing in from the
ends towards the centre helps prevent the
ends from splintering.
Drilling
Hand brace and bit, power drill or drill press
all work easily with plywood. Holes of large
diameter are best cut with a brace and
expansion bit rather than with a high-speed
drill. For power drilling, spur bits give good
results. Reversing the panel as soon as the
bit point is through and completing the cut
from the other side will ensure a clean cut
without splintering.
Power tools will help get a smooth edge. A
power saw with a carbide tip blade can
produce a smooth edge if the first cut is
made more generous than is necessary and
the edge is then cut to size with a hollowground blade. With a jointer it is best to feed
the wood into the jointer head slowly. With a
disc sander, feed the panel slowly against
the sander at a slight angle so that the area
of edge contact is on the downward side of
the rotating disc.
Small holes are readily cut with either hand
or power drills. As a general rule, the larger
the hole the slower the drill speed.
Clean cuts can be obtained with all methods
of drilling, if the panel has firm support and
is backed with scrap wood to prevent
splintering.
Sanding
Routing
When finish-sanding the panel face, work
with the grain using even pressure and
regular strokes. Use fine sandpaper for final
easing and smoothing the edges and for
rubbing down between coats of paint.
Routers can be used to V-groove, shiplap or
rebate edges of panels. Special bits are
available for moulding and chamfering. Use
sharp bits and work carefully across panel.
Deep cuts in panel edges should be made
in two stages. For specific instructions, see
router manufacturer’s literature.
Fasteners
Plywood can be fastened to framing
materials and other materials can be
fastened to plywood with a number of
devices such as nails, staples, screws, bolts,
clips, and glue. Of these, nails, staples, and
glue are the most commonly used.
Bending
Plywood panels can easily be bent when dry
into mild simple curves. Table 5 gives dry
cold bend radii for the most common
plywood thicknesses. As shown in the table,
plywood can be bent more sharply when the
bend is perpendicular to the direction of the
face grain. These radii are based on panels
selected at random with no regard to
defects such as knots, patches and short
grain. Without selection, a small percentage
of panels bent to these radii may be
expected to break. To obtain smaller radii,
i.e. sharper curves, the panels must be
soaked or steamed.
Nails
Nails are available in a variety of lengths,
diameters, heads points, shank styles and
coatings. In Canada, nails are specified by
length and the diameter of the wire used in
their manufacture.
For most construction uses, common nails
will be satisfactory.
Where greater
withdrawal resistance is required, such as in
subflooring and underlayment nailing, ring
thread, spiral or annular grooved nails
should be used. Coated nails are not
generally used with plywood; galvanized
nails usually hold better and are less likely to
cause staining if the plywood is exposed to
the weather.
The length of nail for a specific purpose is
determined by the thickness of plywood
Saw-kerfing the back of the panel to make it
bend more easily is not recommended if the
plywood is to be used structurally.
Compound curves are virtually unobtainable
with a single plywood panel and should not
be attempted.
Edge Finishing
Table 5. Cold Bend Radii
Plywood
Thickness (mm)
Bending Axis Parallel
to Face Grain (m)
Bending Axis Perpendicular
to Face Grain (m)
6, 7.5
8, 9.5
11, 12.5
14, 15.5
18.5, 19
20.5
0.7
1.0
2.4
3.6
4.8
5.8
1.5
2.4
3.6
4.8
6.0
7.0
These radii are theoretical values only and have not been verified experimentally.
8
through which it must be driven. Table 6
gives recommended nail lengths for the
thickness of sanded plywood used in finish
carpentry work and Table 7 gives nail lengths
for use with unsanded plywood. Nail lengths
for the thicknesses of plywood used in
sheathing applications are found in the
sheathing tables.
Staples
Staples are similar in nature to nails and are
often used interchangeably. Staple sizes
conforming to the requirements of the
National Building Code of Canada for
plywood sheathing and subfloor attachment
are given in Table 7.
Screws
Screws are primarily employed to fasten
plywood used in finish carpentry work,
cabinetry, displays and boat building. Screw
sizes for the most commonly used
thicknesses of plywood together with the
diameters of the screw shank clearance and
pilot holes are given in Table 8.
Screws may be counter-sunk but care
should be taken to avoid breaking the
surface grain of the plywood panel.
In general, sheet metal or drywall screws
hold better. Flathead screws set flush have
more holding power than round-head
screws of the same size. Under round head
screws, a washer will give extra strength.
construction. Bolt holes should be 2 mm
larger than the bolts. A tight fit requiring
forcible driving of the bolts is not
recommended. With common bolts, a
washer or metal plate or strap should be
inserted between the plywood and the bolt
head and between the plywood and the nut.
Nuts should be tightened snugly but not so
as to crush the wood under the washer, plate
or strap.
1. Plow bolts have flush heads with fins to
prevent turning.
2. Carriage bolts normally are more useful
with plywood than common bolts.
3. The speed nut system is a bolt with a
self locking sheet metal nut.
One at midpoint for supports up to 600 mm
on centre.
Two at 1/3 points for supports 601 to 1000
mm on centre.
Three at 1/4 points for supports more than
1000 mm on centre.
Using EASY T&G panels eliminates the need
for H-clips, and prevents differential
deflection between adjoining panel edges.
H-Clips
1
2
3
H-clips are panel edge supports in lieu of
H-Clip
Table 6. nails for Sanded plywood used in Finish Carpentry
Nail
Type
Nail Length
(mm)
(in.)
Plywood
Thickness (mm)
6, 8, 11
38
1½
Casing or Finishing
14
38
51
1½
2
Casing
Finishing
17, 19
51
2
Counter sink
Casing or Finishing
Table 7. nails and Staples for Unsanded plywood
Shank clearance
Plywood
Thickness
(mm)
Pilot hole
Grommets and Inserts
Metal grommets and inserts are employed
when plywood is used for removable panels.
Several types are manufactured for this
purpose.
1
blocking.
They are used to reduce
differential deflection between adjoining
panel edges. H-clips should be spaced as
follows:
2
Nail Length
Common
Ring Thread
(mm)
(in.) (mm)
(in.)
Staple Length
(mm)
(in.)
7.5 and 9.5
51
2
45
1¾
38
1½
12.5 to 18.5
51
2
45
1¾
51
2
20.5 to 25.5
57
2¼
51
2
NA
NA
Maximum
Spacing
150 mm on centre along
edges and 300 mm along
intermediate support
1. Staples shall not be less than 1.6 mm in diameter or thickness with not less than 9.5 mm
crown driven with crown parallel to framing.
2. All nails should be long enough that no less than half their length penetrates into the
second member.
Table 8. Screws for plywood
1. Grommet is fitted with countersunk hold
and crimped to form socket for
removable wood screw.
Plywood
Thickness
(mm)
(mm)
(in.)
(No.)
2. Grommet designed for round head
screw has slotted hole for panel
adjustment.
Bolts
Bolts have only limited use in plywood
6
7.5 to 9.5
11 and 12.5
14 and 15.5
17 to 20.5
19
25
32
38
38
¾
1
1¼
1½
1½
6
6
6
8
Shank Clearance
Screw Size
9
10 or 12
(mm)
(in.)
9/64
3.6
9/64
3.6
9/64
3.6
11/64
4.4
4.8 or 5.6 3/16 or 7/32
Pilot Hole
(mm)
(in.)
1.6
1/16
1.6
1/16
1.6
1/16
2.0
5/64
2.4 or 2.8 3/32 or 7/64
certiWood™ Canply plywood Handbook
GLUES AND GLUING
Glues
Glue is playing an increasingly important
role in plywood construction, both in
nonstructural applications such as flush
panel doors, furniture, cabinets and built-ins
and in structural uses such as web beams,
stressed skin panels and similar plywood
structural components.
Because of the many developments in
recent years in the field of wood adhesives,
and the varied conditions of service under
which glued wood products are expected to
perform satisfactorily, the selection of a
proper adhesive is important and is
sometimes a complex problem.
The
following notes on the most common types
of glues in general use today should help
make the selection of a suitable glue for a
specific job somewhat easier. It is important
to note that plywood treated with wood
preservatives or fire-retardants is difficult to
glue. Also, if the wood is to be treated after
gluing, the choice of adhesives is severely
limited.
Casein glue is one of the older woodworking
glues and is still readily available in powder
form. When mixed with water it forms a glue
of moderately high dry strength and
moderate resistance to water, damp
atmospheres
and
intermediate
temperatures. Casein is generally applied
and pressed at room temperature. It is not
recommended for exterior exposure and is
used primarily for laminating structural
timbers for interior use.
Contact and rubber-based glues - other than
those elastomeric construction adhesives
developed specifically for field-glued
plywood subfloors (see page 13) and
affixing plywood wall paneling to studs and
strapping - are not suitable for structural
uses. One of the main disadvantages of
these types of glue is that their dry strengths
are generally lower than those of
conventional wood working glues and the
joint tends to creep under prolonged
loading, losing its original configuration.
This joint deformation remains even after the
load is removed.
Contact adhesives are developed for
bonding two surfaces together without the
use of clamps. Unlike many conventional
wet bonding glues, contact adhesives are
applied to each surface to be bonded,
allowed to dry, then joined together with
pressure. The two dried adhesive coatings
fuse together to form a uniform bond of
immediate strength. Generally speaking,
the higher the pressure, the more uniform
the bond will be.
themselves or other non-porous materials
and include gluing hard or textured surfaced
materials such as metal, high density plastic
laminates, vinyl and other fabrics to plywood
surfaces.
Polyvinyl acetate glues, often called ‘white
glues’, are valuable for non-structural interior
uses such as assembling flush panel doors,
cabinets and furniture. They are not
recommended for exterior exposure
because they are inherently elastic and have
low resistance to heat and moisture. The
glue joint also tends to creep under external
loads and with dimensional changes in the
wood caused by changes in moisture
content.
Synthetic resin adhesives now surpass most
of the older glues in importance for bonding
plywood.
Urea resin adhesives, available in dry
powder or liquid forms, are used extensively
for furniture, cabinet and door construction,
and similar general assembly work. They
are also used in some areas of marine
construction where the joint is not subject to
excessively high temperatures and high
humidity conditions. In general, urea resins
are high in both wet and dry strength,
moderately durable under damp conditions,
and have moderate to low resistance to
temperatures above 50 °C.
Resorcinol, phenol-resorcinol and phenolformaldehyde resin adhesives, similar to the
type of thermo-setting glue used to make
plywood, are required for gluing plywood
and lumber into products that must
withstand stress and exposure to the
elements. Such uses include marine work
and plywood structural components such as
beams and stressed skin panels. For such
high strength uses a glue must develop
shearing stresses between the two surfaces
being joined and therefore should be
stronger than the wood itself in shear. These
three types of adhesives are high in both wet
and dry strength, very resistant to moisture
and damp conditions, and more resistant
than wood itself to high temperatures.
Of invaluable assistance to the glue user is
the technical assistance provided by
adhesive manufacturers. Many reputable
glue manufacturers maintain staffs of
technically trained personnel willing to assist
the glue user in the selection and use of the
type of adhesive best suited to job
requirements.
NOTE: To achieve the optimum glue bond
between members it is imperative that the
glue manufacturer’s recommendations in
regard to wood moisture content, shelf life,
pot life, working life, mixing, spreading,
assembly time, time under pressure, and
ambient temperature be followed.
Gluing
Gluing pressure can be applied to
secondary gluelines (i.e. gluelines other than
the primary gluelines used in the
manufacture of the plywood itself) by many
methods, including weights, presses,
clamps and nails. Whatever the method, it
should be capable of exerting a pressure on
the glueline of 0.7 to 1 MPa.
Weights, presses and clamps are often
impractical for many gluing operations,
particularly in the fabrication of large
plywood structural assemblies. In such
cases, glueline pressure may be developed
by nails - a technique known as nail-gluing.
Nail sizes and spacings for various
thicknesses of plywood are given in Table 9
and are suggested as a guide to nail-gluing.
Nail spacings recommended for nail-gluing
techniques are closer than those
recommended for field glued sub-floors
because in the former the nails are used to
develop uniform pressure along the glueline
Table 9. Guide to nail Gluing
Plywood
Thickness (mm)
Nail Length
(mm)
(in.)
Nail Type
6 to 9.5
38
1½
Common
11 to 20.5
51
2
Common
Common uses for contact adhesives involve
the bonding of non-porous materials to
certiWood™ Canply plywood Handbook
Epoxy resins are used for more specialized
applications such as bonding metals,
plastics and some masonry materials to
themselves and to plywood. Their use in
wood-to-wood bonding is limited since their
permanence has not been adequately
established. Epoxy resins are marketed in
two parts, resin and curing agent, for mixing
at the point of use.
10
Nail Spacing
Nails spacing shall not exceed 75 mm oc
along each row for plywood up to 7.5 mm
thick or 100 mm oc for plywood 12.5 mm
and thicker. One row of nails shall be
used for each 50 mm width or part
thereof of contact area to be glued.Rows
shall be spaced such that the distance to
the edge of the contact area is
approximately half the distance between
rows. Nails in adjacent rows shall be
staggered to provide even glueline
pressure and to reduce the danger of
splitting the lumber.
so that the adhesive can perform as a
structural fastener whereas in the latter, the
elastomeric glue serves primarily to stiffen
the subfloor and prevent movement that
may cause floor squeaks.
SHEATHING, SIDING AND PANELING
Floor Sheathing
General
CertiWood™ EXTERIOR plywood provides
an ideal floor beneath resilient flooring and
carpeting. Plywood goes down flat and
stays flat for a smooth, uniform surface.
When exposed to moisture during
construction, some swelling may occur, but
it is substantially less than panels made with
particles, strands or wafers. Also, when it
dries it returns to its original thickness, thus
eliminating the need to sand the joints
before applying the next layer. EASY T&G
plywood panels may be used to further
reduce labour and material costs by
eliminating the need for costly blocking at
panel edges.
Plywood panels for subflooring and single
layer subflooring should be applied with face
grain perpendicular to supports and with joints
parallel to joists staggered. A 2 mm gap
should be left between all square edges of
adjacent panels. EASY T&G Floor is designed
to butt at the tip of the tongue leaving a 1 mm
gap on the face and underside.
To ensure the best possible performance,
plywood floors should be protected from
rain and snow shortly after installation to
prevent excessive moisture pickup.
Where water permeable finished flooring is
used in bathrooms, kitchens, public
entrance halls and laundry areas, such
flooring shall be installed over a membrane
with a water permeability not exceeding
18 ng/Pa•s•m2
Subflooring
For subflooring that does not come into
direct contact with floor finishing material
and is used under plywood underlayment,
hardwood flooring or concrete, Sheathing
grade plywood is suitable (see table 10).
Table 10. Minimum Thickness of Canply EXTERIOR plywood and
nailing Schedule for Subflooring
Recommendations suitable for residential floors where the National Building Code stipulates the design live
load does not exceed 2.4 kPa. Reduced support spacing and/or greater thicknesses may be necessary for
non-residential construction.
End Use¹
Plywood
Designation
DFP,
CSP,
Aspen
or
Poplar
DFP,
CSP,
Aspen
or
Poplar
Subflooring with panel edges not
supported:
a) Under matched softwood flooring
not less than 19 mm thick laid at right
angles to the joists
b) Under matched hardwood flooring
not less than 7.9 mm thick laid at right
angles to the joists
c) Under separate panel-type underlay
not less than 6 mm thick or with concrete
topping applied to subfloor 4
Single layer subflooring with panel edges
supported by blocking or tongues and
grooves:
a) Under carpeting
b) Under resilient floor finishes3
Plywood
Thickness (mm)
12.5, 15.5, 18.5
20.5
Spacing of Supports (mm)
300 400 480 600 800
Plywood Thickness (mm)
12.5 12.5 12.5 12.5 NR2
12.5 15.5 15.5 18.5 NR
12.5 12.5 NR
NR
NR
12.5 15.5 15.5 18.5 20.5
18.5 18.5 NR NR NR
Nailing Schedule for Subflooring
Size and Type
51 mm (2 in.) Common or
45 mm (1¾ in.) Annular grooved
57 mm (2¼ in.) Common or
51 mm (2 in.) Annular grooved
Maximum Nail Spacing
150 mm around perimeter and
300 mm along intermediate
supports
Single Layer Subflooring
EASY T&G plywood or square-edge
plywood with edges supported by blocking
can be applied to floor joists forming a single
layer subfloor.
Minimum plywood
thicknesses for various support spacings
and finish floorings are given in Table 10.
Select grade plywood is recommended for
single layer subfloors intended for use under
most carpeting.
Single layer subfloors for use under resilient
floor finishes such as linoleum, rubber, and
synthetic sheets or tiles, and some types of
glued-on carpets which normally require the
use of underlayment, are usually referred to
as combined subfloor and underlayment.
This type of subfloor is recommended only
for prefabricated structures or for
applications where panels are fully protected
against damage and moisture before and
after installation and is not permitted for use
under ceramic tiles applied with adhesive.
18.5 mm Select or Select Tight Face cleaned
& sized plywood is recommended for
support spacings up to 407 mm.
For best performance, elastomeric glue
should be applied between plywood and
supports and into T&G profiles before
nailing with annular grooved nails. Final
nailing should be left until the finished
flooring is to be laid, at which time the
plywood should have dried to the
approximate conditions that will exist in the
structure during occupancy. The surface
should be prepared as recommended by
the floor covering manufacturer.
Underlayment
Select or Select-Tight Face grades of
7.5 mm or 9.5 mm plywood, or special
underlayment panels made by several
CertiWood™ members, are recommended
for use as underlayment under resilient floor
finishes such as linoleum, rubber and
synthetic sheets or tiles, ceramic tiles and
those types of glued-on carpets for which
the manufacturer recommends the use of
underlayment. For ceramic tiles applied with
adhesive, 11 mm thick underlayment is
required where supports are spaced wider
than 300 mm on centre.
Underlayment panels should not be installed
until wood subfloors, concrete, plaster and
lumber framing have dried to the
approximate conditions that will exist in the
structure during occupancy.
Also,
underlayment panels should be allowed to
acclimatize in room conditions. To achieve
this, it is recommended that the panels be
placed separately on edge around the room
for a minimum of 48 hours prior to
installation of the finished floor.
1. Plywood shall be applied with face grain perpendicular to supports. 2. NR - Not recommended. 3. When resilient flooring is applied directly to plywood subfloors, the
subfloors shall be fastened to supports using annularly grooved nails and elastomeric glue should be applied between plywood and supports and into T&G profiles.
4.Not applicable where flooring consists of ceramic tiles applied with adhesive.
11
certiWood™ Canply plywood Handbook
Underlayment panels should be laid at right
angles to subflooring panels with joints in
underlayment staggered and offset at least
200 mm from joints in subflooring, and with
ends and edges butted to light contact.
Unless specified otherwise by the
manufacturer, underlayment panels shall be
nailed or stapled every 100 mm around the
perimeter (10 mm to 15 mm from edge), and
every 150 mm throughout the rest of the
panel. Use 25 mm ring grooved underlay
flooring nails, or 28 mm long staples with 5
mm crowns and not less than 1.2 mm shank
diameter. Avoid nailing underlayment to
joists supporting the subfloor. Nailing or
stapling should begin at one corner of the
underlayment panel and should progress
diagonally across the panel.
Preparation of underlayment prior to
applying floor covering should be done as
recommended by the floor covering
manufacturer. Such a recommendation
should include sanding uneven surfaces
and panel joints to level, filling surface voids
according
to
the
floor
covering
manufacturer’s procedure and, when
required by the manufacturer, a procedure
for filling joint seams. It should also include
specification for a suitable filler.
Field-Glued Subfloors
This technique provides stiffer, better quality
floors. With the new adhesives and gluing
techniques available, field-glued combined
subfloor and underlayment plywood floors
save money while providing premium quality
construction. Material and labour costs are
reduced with the single floor system, which
combines the functions of both structural
subflooring and smooth underlayment in a
single layer of plywood. Floor stiffness is
also increased from 20% to 70% (depending
upon the size and spacing of the joists and
thickness of plywood) compared to
conventional floor construction because the
glued plywood floor and joists act together
as a composite, stiff T-beam unit.
apply according
instructions.
to
manufacturer’s
The Canadian General Standards Board
Specification CAN/CGSB - 71.26 - M 88
establishes minimum performance and test
requirements for elastomeric construction
adhesives for bonding plywood to lumber
framing.
Gluing Conditions
Glues are formulated to provide adequate
bonds and unseasoned lumber, which
makes their use practical under normal site
Hardwood
flooring
Resilient flooring
CANPLY Select
grade plywood
underlayment
Underlayment used
to compensate for
difference in thickness between resilient
and wood flooring
Wall to wall
Carpet
certiWood™ Canply plywood Handbook
CANPLY
Sheathing grade
plywood subflooring
Edge blocking
(not necessary
with EASY T&G
plywood)
Resilient flooring
CANPLY Select
grade underlayment
Underlayment used
to compensate for
difference in thickness between carpet and
resilient flooring
Builders who have adopted this floor system
have experienced an added benefit minimum call backs to repair floor squeaks.
With field-glued plywood subfloors, the glue
firmly bonds the plywood and joists together
to help prevent the differential movement
between the joists and the subfloor which
causes squeaks.
Glues
Several brands of elastomeric glue suitable
for field use are available from building
supply dealers. Most are conveniently
packaged in spouted, ready-to-use
cartridges for caulking guns. Some brands
are available in bulk for use with portable
pneumatic systems.
These special
construction adhesives are not be confused
with ordinary drywall glues. Use only glues
specified for construction purposes and
conditions. With several of the adhesives
available, gluing can be done in below
freezing weather provided the temperature
rises above freezing reasonably soon after
the floor is applied. However, for best results
the ambient temperature should be above
freezing. Gluing should never be done when
temperatures are continually below freezing
because none of the adhesives currently
available can develop adequate shear
strength under such conditions.
The
adhesive should be kept as warm as
possible during cold weather to ensure ease
of application.
EASY T&G
Sheathing grade
subfloor
Resilient flooring
EASY T&G
Select grade
Cleaned and Sized
single layer subfloor
Combined subfloor
and underlayment
Plywood Subfloor and Underlayment
12
Application of EASY T&G Plywood for Regular
and Field-Glued Plywood Subfloors
It is advisable to plan placement of EASY
T&G panels to minimize cutting, waste and
labour. Panels should be placed with the
face grain at right angles to the supports.
End joints, which must occur over supports,
should be staggered. When placing the
tongued edge of a panel into the groove of a
previously placed panel, care should be
taken to ensure that tongues and grooves
are not damaged. Note that each T&G
panel is stamped “THIS SIDE DOWN” to
ensure
correct
placement.
The
recommended application sequence for
EASY T&G plywood is as follows:
1. It is important that the first row of panels
be aligned straight and true. To ensure this,
measure a panel width in from the ends of
the two outside joists and snap a chalk line
between these points. This line will also act
as a boundary when applying glue for the
first row of panels of a field-glued plywood
subfloor.
panels at a time (unless the glue
manufacturer’s instructions permit covering
a larger area in advance of laying the
panels). See Table 11 for glue coverage.
Nail panels securely in position taking care
not to nail within 150 mm of the grooved
edge until the tongues of the following row
are in position.
3. Place a second row of EASY T&G panels
along the other side of the chalk line with the
tongues fitting into the grooves of the panels
in the first row and having the end joints
between plywood panels staggered relative
to the first row.
Do not attempt to force a tight joint between
panel faces as the EASY T&G Floor is
designed to butt at the tip of the tongue
leaving a 1 mm gap on the face and
underside. A 2 mm gap should also be left
between panel ends to allow for expansion
of the plywood and shrinkage in the joist
thickness.
Table 11. approximate Glue Coverage vs Bead Size
Bead Diameter
(mm)
Litres
per 100 metres
Metres
per Litre
3
5
6
8
10
0.7
2.0
2.8
5.0
7.9
142
51
35
20
13
Note: 1 U.S. gallon equals 3.78 litres; 1 Imperial gallon equals 4.54 litres
If EASY T&G plywood is used, no
blocking is necessary
2. For a regular subfloor, lay the first row of
EASY T&G panels with the grooved edge
along the chalk line and tack in position with
four to six nails per panel. Do not nail within
150 mm of the grooved edge in any row until
the tongues of the following row are in
position.
For a field-glued plywood subfloor, lay a
3 mm to 6 mm diameter bead of glue along
the joists or beams apply glue in a
serpentine pattern. Where panel ends will
butt on the joists, lay two beads of glue to
ensure that each panel end will be glued.
Apply only enough glue to lay one or two
1
Edge blocking for
square edge
plywood
CANPLY plywood
splice plates
Where joists are
continuous over bearing
points, they may be
end-butted, not lapped, to
provide continuous nailing
Beam
Joist
Spliced Floor Joists
MAINTAIN PROPER GAPS
DO NOT FORCE PANELS
TIGHTLY TOGETHER!
• Leave “built-in” 1 mm
expansion gap
between tongue and
grooved edges.
• Leave a 2 mm gap
between panel ends.
2
Lay panels with face grain
across the joist
Face
Gr
Direc ain
tion
3 Fasteners spaced 150 mm (6") around the perimeter of the panel
and 300 mm (12") on intermediate supports. For plywood thicknesses up
to 18.5 mm, Code approved fasteners include 51 mm common or spiral nails,
51 mm staples and 45 mm ring thread nails or screws.
NOTE: Adding a bead of
elastomeric glue between
joist and panel helps
eliminate squeaks and
nail popping, and
increases floor stiffness
resulting in potentially
longer spans.
EASY T&G Floor Installation
13
certiWood™ Canply plywood Handbook
4. Sheathe the remaining floor area. For a
field-glued subfloor apply glue in advance of
each panel and nail each panel securely in
place within the glue manufacturer’s
specified assembly time. For extra stiffness,
a bead of glue, either continuous or
intermittent, may be squeezed into the
grooves before mating the panels. If
applying a regular subfloor, the panels can
be nailed securely to the joists at this stage.
If the plywood is being used as combined
subfloor and underlayment as a base for
resilient flooring, panel nailing should be left
until the finish flooring is to be laid, at which
time nailing should be completed and the
nail heads set.
5. Protect floor from excessive moisture.
Hints to Reduce Nail Popping in Floors
Nail popping is the term used to describe
the tendency of some nails to rise above the
plywood surface after driving. It becomes a
problem in subfloor and underlayment
applications only if nails are driven into
unseasoned lumber joists. As the lumber
shrinks, the whole depth of the joist is
reduced, including the depth of the nail hole.
With the nail hole reduced in depth the nail
head is raised above the surface of the
plywood because the nail itself cannot
increase the depth of the hole. This causes
humps or blisters on the surface of resilient
flooring. The tendency for nails to pop can
be reduced by:
1. Selecting lumber joists so that members
with similar crowns will be placed side
by side.
2. Using dry products, such as k.D. lumber
or engineered I-Joists, whenever possible. If
unseasoned lumber is used do not fasten
plywood permanently until the joists have
attained equilibrium moisture content.
wall and provide a flush surface for the
exterior siding material. A small gap should
be left between panels to allow for
expansion.
3. Using the shortest possible annularly
grooved nails consistent with the
recommendations given in Table 10. Drive
nails at a slight angle and set all nail heads
prior to laying resilient flooring.
Siding and Paneling
Wall Sheathing
CANPLY EXTERIOR plywood used as wall
sheathing stabilizes the building framework
and makes diagonal and corner bracing
unnecessary. Damage to finish materials in
the structure due to uneven settling of the
frame is minimized when plywood sheathing
is used because plywood adds rigidity to the
building. This rigidity is especially important
when walls are prefabricated on the floor
and then tilted into position, or where walls
are to contain large areas of glass. Plywood
sheathing also contributes to the overall
thermal performance of the wall because the
large panels mean fewer joints through
which air can leak and heat can escape.
Minimum plywood thicknesses for wall
sheathing are given in Table 12. For
maximum performance of the plywood,
panels should be applied with the face grain
perpendicular to the studs. Plywood panels
should not be applied to form a tie between
the bottom plate and the floor joists or
header or sill, since shrinkage of the lumber
may cause the plywood sheathing to buckle.
A strip of plywood along the joist header, as
shown in the illustration below, will extend
sheathing to the required lower limit of the
Top plate
Open Joint
Studs
Stagger panels
for maximum
strength
Leave 2 mm gap
between panel
edges. In wet
service conditions,
increase gap to
3 mm
EASY T&G
plywood Subfloor
Joists
CANPLY plywood strip
Sill plate
Foundation
Header
Plywood Wall Sheathing
certiWood™ Canply plywood Handbook
14
Combined Sheathing and Cladding
This siding system, sometimes called a
single skin finish, is a sound and economical
method of wall construction in which
plywood is applied directly to the studs to
perform the dual role of structural sheathing
and finish siding.
Available in a range of patterns and textures,
plywood siding panels combine the natural
characteristics of wood - warmth, beauty
and durability - with the superior strength
and stiffness imparted by cross-laminated
construction. This form of construction is
one of the least expensive ways to enclose
space and is suitable for most types of
buildings.
Minimum thickness requirements, support
spacing and nailing schedules for plywood
siding are given in Table 13.
Plywood Siding
Plywood can be used in panel form or cut
and applied as lap or level siding. Sheathing
grades of plywood make an economical
cladding with a pleasing rustic appearance.
These grades are especially attractive when
the plywood is stained with a heavy bodied
stain and the joints are covered with battens
or moulding. When the plywood is to be
painted, Medium Density Overlaid plywood
should be used. This type of plywood has a
smooth, durable, resin impregnated surface
ideal for a long lasting paint finish. Textured,
grooved, factory-primed and pre-finished
siding panels are also available. Hot-dipped
galvanized nails should be used with
plywood siding to avoid rust streaks. It may
be desirable to use colour-matched nails for
some pre-finished panels. If battens are
applied over pre-finished siding, the battens
should be nailed separately so that they can
be removed for refinishing without
damaging the siding.
Wood, Metal and Vinyl Siding
Siding should be nailed directly to the studs
through the sheathing. All vertical joints
should occur over studs. Nails should be
corrosion-resistant.
Red Cedar Shingles and Shakes
Plywood applied perpendicular to the studs
provides a stiff nailing base for shingles and
shakes. They should be nailed directly to
the sheathing with hot-dipped galvanized
nails driven flush but not so that the head
crushes the wood.
Stucco
If self-furring metal lathe is used, it may be
nailed directly over the plywood sheathing
after applying building paper. Nails should
be hot-dipped galvanized, have large heads
and be driven through the plywood into the
studs. If wire mesh is used, it should be
attached with furring nails.
Brick or Masonry Veneer
Plywood sheathing should be covered with
asphalt-impregnated paper lapped 100 mm
at the edges. Brick or masonry should be
set at least 25 mm from face of sheathing.
Metal ties may be secured by nailing
through the sheathing to the studs.
Table 12. Minimum Thickness of Canply EXTERIOR plywood and
nailing Schedule for Wall Sheathing
(Recommendations suitable for Housing and Small Buildings governed under
Part 9 of the National Building Code of Canada)
Spacing of
Supports (mm)
Plywood
Thickness (mm)
300, 400
6
480, 600
7.5
Nailing Schedule for Wall Sheathing
Size and Type
51 mm (2 in.) Common
or
45 mm (1¾ in.)
Annular grooved
Maximum Nail Spacing
150 mm around the
perimeter and 300 mm
along intermediate
supports
1. Plywood may be applied with face grain parallel or perpendicular to supports.
2. A 2 mm gap shall be left between panel edges. Gap shall be increased to
3 mm in wet service conditions.
3. If asbestos cement shingles are to be attached to the sheathing only, plywood
shall be not less than 9.5 mm thick.
4. If vertical lumber siding or stucco lath or reinforcing are to be attached to the
sheathing only, plywood shall be not less than 12.5 mm thick.
5. If vertically applied metal siding or wood shingles and shakes are to be
attached to the sheathing only, plywood shall not be less than 7.5 mm thick.
Table 13. Minimum net Effective Thickness of plywood Siding and nailing Schedule
Spacing of Supports (mm)
300
Condition of Use
Without sheathing or over furring:
Face grain parallel to supports
Face perpendicular to supports
With sheathing:
Face grain parallel to supports
Face grain perpendicular to supports
400
480
600
Minimum Net Effective Plywood
Thickness (mm)
8
6
6
6
11
8
8
6
6
6
6
6
11
8
6
6
Nailing Schedule for Plywood Siding
(see note 6 for lap or bevel siding)
Size and Type
52 mm (2 in.)
corrosion-resistant
common nails
compatible with siding
for plywood thicker
than 7 mm and 38 mm
(1½ in.) nails for
plywood up to 7 mm
thick
Maximum
Nail Spacing
150 mm on centre
along edges and
300 mm along
intermediate supports
1. Net effective thickness: For brushed, grooved, striated and saw textured plywood, the net effective thickness is the thickness between the bottom
of the scores or grooves and the back face of the plywood.
2. The edges of plywood siding shall be treated with a suitable paint or sealer.
3. Plywood applied in panels must have all edges supported. No less than a 2 mm gap shall be provided between the panels. Gap shall be
increased to not less than 3 mm in wet service conditions. Vertical joints in such siding shall be protected with batten strips or caulking when the
plywood joints are not matched. Horizontal joints shall be lapped not less than 25 mm or shall be suitably flashed.
4. Plywood applied in horizontal lapped strips shall have no less than a 2 mm gap (3 mm in wet service conditions) provided at the butted ends,
which shall be caulked. The horizontal joints shall not be lapped any less than 25mm. Wedges shall be inserted under all vertical butt joints
and at all corners when horizontal lapped plywood is applied without sheathing.
5. Building paper is not required with panel-type siding provided all joints are caulked and either covered with battens or suitably factory-detailed to
exclude moisture.
6. Nails for lap or bevel siding shall be 51 mm corrosion-resistant and compatible with the siding. Nails shall be spaced 100 mm oc at vertical
joints and one nail per stud along bottom edge of siding.
7. Clearance of no less than 200 mm shall be provided between the finished ground level and plywood siding and no less than 50 mm between
roof surface and plywood siding.
15
certiWood™ Canply plywood Handbook
Joints - no caulking required for factorydetailed joints or where the joints are
covered with battens or backed with
building paper.
Joints - no caulking required for factorydetailed joints or where the joints are
covered with battens or backed with
building paper.
Leave 2 mm gap between panels edges.
In wet service conditions, increase gap
to 3 mm.
Leave 2 mm gap between panels edges.
In wet service conditions, increase gap
to 3 mm.
No diagonal wall
bracing required with
single skin construction
No diagonal wall
bracing required with
single skin construction
Insulation as required
Insulation as required
Batten (nails
through batten
should penetrate
stud at least 25 mm
CANPLY plywood panel siding
CANPLY plywood panel siding
Uniform Panel - Board and Batten
Grooved Panel - Vertical
Joints - no caulking required for factory-detailed vertical joints or
where the joints are covered with battens or backed with building
paper. Leave 2 mm gap between panels edges.
In wet service conditions, increase gap to 3 mm.
No diagonal wall
bracing required with
single skin construction
Lap or
lash
horizontal
joints.
Insulation as required
Insulation as required
Blocking at
horizontal joints
Building paper
Battens to
conceal butt
joints at panel ends
Shingle wedge
under vertical joints
(lap siding only).
Stagger butt joints
over studs
CANPLY plywood panel
siding installed horizontally, nail as
required for vertical application
CANPLY plywood lap siding
Grooved Panel - Horizontal
Lap Siding
Typical Wall Construction Details:
Note: Not all construction details are shown in above diagrams. Wall assemblies should be designed according to local building code requirements and conditions.
certiWood™ Canply plywood Handbook
16
Table 14. Minimum Thickness of Canply EXTERIOR plywood and
nailing Schedule for Roof Sheathing
Recommendations suitable for designs governed by Part 9 of the National Building Code of Canada and/or
where the design live load does not exceed 2.4 kPa
Plywood
Designation
Method of Edge Support
Corner Boards
Flat Panel
Corner Boards
Lap or Bevel
Panel edges supported by
EASY T&G roof edge profile
DFP EASY T&G
CSP EASY T&G
Panel edges not supported
DFP,
CSP, Aspen or
Poplar
7.5, 9.5, 11, 12.5
15.5, 18.5
20.5
7.5
7.5
7.5
7.5
Spacing of Supports (mm)
400 480 610 800 1200
Plywood Thickness (mm)
7.5
7.5
9.5
9.5
9.5
9.5
9.5
9.5
12.5 18.5
15.5 20.5
11
11
11
11
12.5
12.5 12.5 15.5 NR
12.5 12.5 15.5 NR
Nailing Schedule for Roof Sheathing
Plywood
Thickness (mm)
Butted
DFP
CSP, Aspen or
Poplar
Panel edges supported by
blocking or H-clips
300
Size and Type
Maximum Nail Spacing
51 mm (2 in.) Common or
45 mm (1¾ in.) Annular grooved
150 mm around the perimeter
and 300 mm on centre along
intermediate supports except
that when primary supports are
spaced greater than 800 mm on
centre, nails shall be spaced at
150 mm intervals along all
supports.
57 mm (2¼ in.) Common or
51 mm (2 in.) Annular grooved
Butted
Square Corner
Flat Panel
Notes:
1. EASy T&G panels are available in thicknesses of 11 and 12.5 mm, and are recommended for
superior performance as roof sheathing. For details, see pages 18 and 19.
Corner Stop
2. Recommendations suitable for flat, flat-pitched or pitched roofs. Because of point loads, which
may be imposed during construction, the tabulated thicknesses should not be reduced nor the
tabulated spans increased. For thickness of roof sheathing on a flat roof used as a walking
deck, follow the recommendations for flooring in Table 10.
3. Plywood shall be applied with the face grain perpendicular to supports.
Butted
Square Corner
Lap or Bevel
4. Plywood shall be applied so that joints parallel to rafters are staggered and all adjacent
edges are separated by no less than a 2mm gap. In wet service conditions, the gap should be
increased for all panels except EASy T&G to no less than 3mm.
5. DFP - Douglas Fir Plywood meeting CSA O121.
6. CSP or Aspen - Canadian Softwood Plywood meeting CSA O151.
7. Poplar Plywood meeting CSA O153.
8. NR - Not recommended.
Corner
Moulding
Paint
Open Joint
Typical Exterior Wall Corner Details
17
certiWood™ Canply plywood Handbook
Soffits
Plywood cut to correct size and nailed
directly to roof joists, rafters or outriggers
can act as soffits. Use 6 mm for supports up
to 400 mm on centre and 7.5 mm for
600 mm spacings. Cut-to-size and vented
soffits are available from many building
supply dealers. It is a good idea to stain or
prime the soffit panels before installation.
This will save much work later. MDO
provides a superior paint surface.
The illustrations opposite show two methods
of placing vents in plywood soffits.
Sloped Soffit
Rafter
CANPLY plywood
roof sheathing
Top Plate
Wall studs
Fascia
CANPLY plywood
wall sheathing
Roof Sheathing
Plywood roof sheathing offers time and
money saving advantages while contributing
to the overall strength and rigidity of the
structure. In some cases it may be possible
to reduce roof construction costs by using
fewer rafters spanned by a thicker than usual
sheathing panel. The high-strength, low
weight, skid-resistant deck provided by
plywood sheathing is ideal for all type of
roofing materials, from red cedar shingles
and shakes to built-up roofing.
Table 14 gives minimum requirements for
the application of CANPLY EXTERIOR
plywood roof sheathing. Panels should be
applied with the face grain at right angles to
supports to obtain maximum strength. A
small gap should be left between panels to
allow for expansion.
CANPLY plywood soffit
Horizontal Soffit
Intermittent screened
soffit vents
Rafter
Top plate
CANPLY plywood
roof sheathing
Stud
Fascia
Continuous nailer
Outrigger
CANPLY plywood
wall sheathing
CANPLY
plywood soffit
Screen vent runs
length of soffit
Vented Soffits
During construction, the rafter header
should be applied first. The first row of
plywood panels should then be nailed flush
with the outside edge of the header to give a
true roof edge. The fascia board is then
applied to cover the rafter header and the
edge of the plywood sheathing. This
method of construction will also help stop
leakage into the soffit if water should back
up the eave.
For maximum strength, place
plywood panels across rafters
and stagger joints
No H-Clips required with EASY T&G
H-clips are an alternative to solid blocking in
conjunction with 9.5 mm plywood roof
sheathing spanning rafters placed 600 mm
apart, subject to the following conditions:
1. One H-clip shall be placed midway in the
joint of abutting sheets between each pair of
rafters or joists. Rafter or joist spacing shall
not exceed 600 mm.
2. H-clips should fit snugly.
Grain
Face ion
t
e
ir
D c
Roof rafter
Top plate
Fascia
See Table 14 for
nail spacing
Rafter header
3. Abutting plywood sheets shall be fitted
as closely as clips permit, providing the
separation required by the National Building
Code is maintained. Occasional misfit of
abutting sheets may be tolerated providing
resulting gaps at maximum opening do not
exceed 6 mm.
EASY T&G Roof Sheathing
certiWood™ Canply plywood Handbook
Leave 2 mm gap
between panel edges.
In wet service conditions,
increase gap to 3 mm
18
An alternative to sheathing with regular
CANPLY plywood is to use EASY T&G
panels. These panels are manufactured
specially for roof sheathing and have a new,
patented edge profile that results in a stiffer
roof and eliminates differential deflection as
well as the need for H-clips. Table 14 gives
thickness and nailing recommendations.
Install EASY T&G with tongued edge up (i.e.,
pointing toward the top of the roof). An
exception may be made where triangular
cut-offs are made, such as when sheathing
hipped roofs. When square edge plywood
is used on hipped roofs, the triangular cutoffs are flipped over and used on the other
end of the same row. This is not possible
with EASY T&G when all panels are installed
with tongued edge up. Instead, install one
side of the roof with the tongued edge up
and the other side with the tongued edge
down (i.e., pointing toward the eaves). The
triangular cut-offs from one side of the roof
can then be used on the other side with no
loss of footage.
Panels should be installed with the grain
across supports and applied so that joints
parallel to rafters are staggered. A 2 mm
gap between the ends of adjacent panels is
required. Correct spacing between the long
edges of adjacent panels is inherent in the
design of the edge profile.
Finish Material over Plywood Roof Sheathing
Many types of roofing materials have proven
satisfactory under various service conditions
when applied over plywood roof sheathing.
The most common materials used on
sloping roofs are Western Red Cedar
shingles and shakes, asphalt shingles and
tiles. For flat or flat-pitched roofs, built-up
roofing is generally used. Rolled roofing is
suitable for temporary use but is not
recommended for permanent installation
over plywood roof sheathing.
When a plywood flat roof deck is to carry
pedestrian traffic, it must be considered as a
floor or walking deck and the plywood
thickness selected accordingly. Surface
membranes conventionally used as roof
coatings are rarely suitable for pedestrian
traffic and should not be used on walking
decks. However, special coatings which are
both waterproof and abrasion-resistant have
been developed in recent years and their
use on plywood walking decks is
recommended.
PERMANENT WOOD FOUNDATIONS
Permanent Wood Foundations (PWFs) are a
complete wood-frame foundation system for
low-rise residential, school, industrial,
commercial and other types of buildings.
Built with preservative treated wood, they are
an extension of the familiar wood-frame
system with the frame walls carried below
ground to serve as the foundation.
The first documented uses of wood
foundations of this type were in the Mark III
and IV experimental homes built in 1961 and
1963 at Canadian Forces base, Rockcliffe
(Ottawa) by the National House Builders
Association (now the Canadian Home
Builders’ Association), in cooperation with
Canada Mortgage and Housing corporation,
the Institute for Research in Construction
and Forintek Canada. The foundation walls
for both homes were built of preservative
treated lumber framing and plywood
sheathing.
Forintek Canada scientists have inspected
those wood foundations regularly since
construction and report that treated wood
foundations can be expected to perform as
well as similarly treated wood in ground
contact in other situations.
Good
performance of treated wood in ground
contact has been well established. Many of
the major structures of the world are
supported on preservative-treated wood
piles, another form of wood foundation.
In the Permanent Wood foundations system
all wood exposed to decay hazard is
pressure treated with preservatives. The
preservatives permanently impregnate the
wood cells to penetration and concentration
levels that make the wood resistant to attack
by decay organisms and termites. The
treated wood is then dried, resulting in an
odourless product with a colour
characteristic of the preservative used.
Wood foundations lend themselves to plant
fabrication or to on-site construction. If the
foundation wall panels are fabricated in the
plant, they can be assembled on jig tables
used to frame the upper walls. This speeds
up erection at the site, and usually results in
cost savings and improved quality control.
The plywood-sheathed wood frame
provides automatic dimensional controls
because plywood panels are square and are
manufactured to precise dimensions.
Construction can take place in most weather
conditions, and can be completed faster
than with traditional foundations, resulting in
reduced construction and lower labour
costs.
The PWF system has many advantages over
conventional foundations such as more
comfortable living areas, speedier erection
and reduced energy costs.
Wood frame foundation walls are readily
insulated to the same high standards as the
rest of the house, resulting in warm, low-cost
living space. They can be finished on the
interior and on the exposed exterior with
conventional coverings and finishes.
Construction details, including plywood
sheathing thickness recommendations, for
19
the PWF system are fully detailed in the
Canadian Wood Council publication
Permanent Wood Foundations, and in CSA
Standard S406 Construction of Preserved
Wood Foundations.
CONCRETE FORMS
CANPLY EXTERIOR plywood is suitable for all
concrete forming applications. Load/span tables
for various thicknesses of CANPLY EXTERIOR
Douglas Fir plywood, together with other design
data, are given in the CertiWood™ publication
Concrete Formwork.
The Advantages of Plywood for Concrete
Forming
The selection of formwork materials should
be based on maximum overall operating
economy consistent with safety and the
quality of finish required. Many contractors
have found that, for the reasons noted
opposite, CANPLY EXTERIOR plywood
satisfies the requirements of economy,
safety and quality for the majority of concrete
formwork applications.
Handling
It is generally acknowledged that the
greatest damage to forms occurs during the
various handling operations. Thorough
planning of the whole forming operation will
keep handling to a minimum. In the interests
of speed and efficiency, mechanical
handling devices should be used whenever
possible.
To slow the drying rate and minimize face
checking, panels should be stored on a flat
dry surface and stacked face to face.
Panels should be protected against sun and
rain but free air circulation must be provided.
Release Agents for Plywood Concrete
Forms
The application of a release agent to the
form face facilitates stripping the formwork
and prevents scaling of the concrete surface
when the forms are removed.
Many proprietary brands of release agents
are available in North America. These
brands vary in composition to suite various
applications but may for general purposes
be divided into three broad categories:
lacquers and paints, oils and greases, and
emulsions.
It is recommended that
contractors use only proprietary brands of
release agents applied according to the
manufacturer’s instructions.
Stripping
To minimize damage during form removal,
stripping procedures should be studied
during form planning with reference to
surface contours and special conditions.
certiWood™ Canply plywood Handbook
While forms must be left in place a sufficient
time to permit proper curing and protection
of the fresh concrete, it is generally desirable
to remove forms as soon as these
requirements have been met.
CANPLY EXTERIOR plywood is a rugged
material, but like other types of panel forms,
plywood can be damaged by prying with
crowbars or by dropping panels on their
edges from a height. If a good release agent
has been properly applied to the plywood,
stripping should present no difficulty.
If it is necessary to use force, wooden wedges
should be used rather than metal pries.
Cleaning
Proper supervision of forming operations on
the job site should extend to the cleaning
and repair of forms. Plywood forms, in
common with all other types, should be
cleaned immediately after stripping.
Concrete particles may be removed by
using a wide blunt blade, straw broom or
burlap. Many contractors use a powerdriven nylon brush. There are also several
proprietary solutions available for softening
concrete adhering to the plywood.
Projecting nails should be withdrawn to
prevent scarring of panels when stacking.
Panels should be stacked flat, preferably out
of the sun to reduce face checking.
Hardware for Plywood
Concrete Forms
Contractors should obtain their hardware
only from recognized suppliers who can
furnish proof of the strength of their
accessories by laboratory or field tests.
Although many different types of form
hardware have been developed, all standard
types are suitable for use with plywood. Of
particular interest are various kinds of high
tensile steel ties or bolts which have been
specifically designed for plywood.
Snap-ties made from high tensile wire are
popular as an inexpensive method of form
support. These ties are designed to prevent
the forms from separating under pressure.
Stripping the forms should be done only
after concrete has set. After the forms have
been removed, a tie breaker is applied to the
Plywood forms should be clean and dry
before repairs are carried out. Where the
grade of plywood and the type of form are
suitable, the plywood may be reversed.
Small splits and depressions can be filled
with a suitable patching compound sanded
flush. Unwanted holes through the plywood
may be patched by:
1. Driving a wooden plug in tightly and
sanding flush.
2. Backing up the hole with scrap wood,
filling with patching compound and
sanding flush.
3. Driving a metal patching disc into the
plywood face.
Experience has shown that even if a
plywood form is damaged beyond
economical repairs, the plywood itself can
be salvaged and usefully re-employed in
numerous fields, for example as stiffening
gussets on new formwork, as rough
foundation formwork, and in those areas
where formwork is difficult to remove and
must be left in place.
certiWood™ Canply plywood Handbook
For most commercial concrete finishes a rod
or bar tie with integral spreaders is
customary. Such ties generally have a notch
or similar reduction in section which allows
the tie to be broken back a set distance from
the wall surface.
Detailing for Plywood
Formwork costs can be substantially
reduced if certain basic details of
dimensioning are borne in mind by building
planners. Beams and columns preferably
should have the same outside dimensions
from foundation to roof, allowing beam and
Why Plywood for Formwork?
Strength
Cross-lamination of veneers tends to equalize strength of panel
with and across face grain, permitting the panel to act as a plate
when suitably supported.
Impact Resistance
Cross-lamination results in high resistance to impact.
Split Proof
Nails can be driven close to panel edge without causing splitting.
Stability
Construction of plywood creates a panel which is shrink resistant.
Less Handling
Large panel size reduces number of pieces required. Reduces
on-site labour.
Reusability
The number of re-uses is related to care in handling and stripping, and reduction of panel cutting my modular detailing. Five to
20 uses are common for quality finish industrial work. Between
50 and 100 uses can be expected for residential foundations.
Fewer Joints
With fewer joints than boards and other materials, plywood forms
are tighter. There is less leakage.
Insulation
Plywood helps protect concrete from rapid temperature changes
and assists in retention of concrete heat in freezing weather.
Salvage Value
Even after many re-uses, plywood may be put to work in
countless other applications such as subflooring, ramps,
protective barriers and temporary structures.
Easy to Bend
Plywood can be bent dry to radii determined by thickness of
plywood, direction of bend and the bending procedure itself.
Soaking or steaming permits bending to shorter radii. (Table 5)
Smooth Face
Large, flat plywood panels provide a concrete surface of uniform
smoothness. Rubbing down and filling are kept to a minimum.
Simplicity of Repair
Complex tools are not needed to patch and repair plywood.
Less Storage Space
Uniform size of large, flat plywood panels makes them easy to
store - on or off the job.
T&G Edges Available
Tongue and groove plywood panels may be used to construct
forms on the site, eliminating the need for blocking at panel
edges and providing a smooth, joint free surface.
Ease of Fabrication
Plywood is easily sawn, bored, routed, etc., with ordinary woodworking tool and therefore lends itself to special requirements of
custom form jobs.
Repairing
It is recommended that plywood forms be
inspected after each use and repairs such
as patching or renailing carried out as
required.
exposed end of the snap-tie and bent at
right angles as close to the wall surface as
possible. The unit is then turned with a
clockwise circular motion until the snap-tie
breaks at break-off point.
20
Nails to fasten plywood to supports should
be as small and as few as practical. For
plywood up to 14 mm thick, nails should be
44 mm ( 1 3/4”) long. For 17 mm plywood
nails should be 51 mm (2”) long.
Wall Forms: Panel Systems
In forming of large areas, standard sized
prefabricated panels can be used for most
structures. As the ties pass through predrilled holes it is essential that the forms be
aligned correctly on a level footing. Panel
form systems can be divided into two broad
classes - unframed and framed.
Unframed Forms
Unframed forms are usually 19 mm plywood
panels. The number of studs or walers is
limited. Forms are aligned by means of toe
plate and top waler. Ties are inserted
through holes cut in the panels. A slipthrough bar or rod passed through the ends
of ties holds panels together. Forms of this
type are most commonly used for residential
and other foundations below grade, and for
concrete walls above grade where the
highest architectural finish is not required.
They are easy and light to handle, requiring
Miscellaneous Forms
A wide variety of decorative effects can be
achieved by pouring concrete into
prepared moulds constructed of plywood.
To achieve these special effects, plywood
can be bent when dry into mild, simple
curves.
Table 5 gives dry, cold-bend radii for most
common thicknesses of plywood.Note that
plywood can be bent more sharply when
the bend is perpendicular to the direction of
the
face
grain
rather
than
across its width. To obtain sharper curves,
the plywood must be soaked or steamed.
Saw-kerfing the back of the panel to make
it bend more easily is not recommended for
structural applications such as concrete
formwork.
600 mm 300 mm
Slab Forms
Plywood is easily adapted to accommodate
a variety of support spacings and section
changes in slab forming. Concrete may be
poured on panels placed directly over
supporting framework. In all cases, the
formwork must safely support the vertical
and horizontal loads placed upon it.
Framed Forms
600 mm
Column Forms
There are several methods of forming
square and rectangular columns. Whenever
possible, the size of the column should be
selected to permit the use of standard 1220
mm by 2440 mm plywood panels.
2400 mm
Framed forms assist in the production of the
highest quality wall obtainable and by the
nature of their construction withstand
rougher use than unframed forms. This form
system lends itself to gang forming.
300 mm 600 mm
Wall Forms: Site Built
It is economical to fabricate as much of the
formwork as possible on the ground, making
sections as large as can be conveniently
handled by the lifting equipment or
manpower available. Where small pieces
are required for such things as stepdowns
and special shapes, plywood can be cut to
the exact size required. Horizontal joints
between panels may be backed up by
headers or nailing strips to eliminate leakage
and produce a smoother joint. For special
circumstances where a smooth joint-free or
fin-free surface is required, the use of tongue
and grove plywood with the joints taped with
thin, pressure-sensitive plastic tape should
be considered. It should be noted however
that special care must be taken to prevent
damage to the T&G edges.
For winter concreting, formwork should
prevent both heat and moisture loss.
Plywood forms are particularly suitable in
this respect because of their good insulating
properties. In some cases plywood forms
have been found sufficient protection at
temperatures between -4 °C and -1 °C to
avoid use of extra insulation, except at
corners and exposed concrete surfaces
where heat losses are higher. At lower
temperatures, insulated reusable plywood
panels have been employed with good
results, especially with heated concrete.
450 mm
If column centres are set so that the distance
between faces of beams is a multiple of the
panel width plus an allowance to facilitate
panel removal, whole panels of plywood
may be used without cutting for slab forms.
Framed Forms
These forms consist of a plywood face from
11 mm to 19 mm with wood or metal frames.
750 mm
It is highly desirable that column, beams
stairwells and other items be so
dimensioned that 1200 mm by 2400 mm or
1220 mm by 2440 mm panels of plywood
can be cut with a minimum of waste.
Below -1 °C, common practice is to use
heated enclosures or insulating coverings, in
addition to heating the concrete itself.
750 mm
A column should preferably be the same
width as a beam framing into it. The column
form then becomes a rectangular or square
box with no cutouts, and the slab forms do
not require cutting at the column
corners.
little framing lumber. Fabrication by the
contractor is simple. Another advantage is
that both faces of plywood can be used.
450 mm
column forms to be re-used without
alteration.
A standard 600 mm by 2400 mm light
modular framed panel of 17 mm plywood
and 38 mm by 89 mm lumber
Precautions When Forming in Hot and Cold
Weather
Hot Weather
In hot weather, concrete must be kept
moist during the curing period. Plywood
forms will prevent almost all moisture
leakage, but exposed surfaces should be
covered with wetted tarpaulins or curing
membrane. It is also advisable to spray
the exterior surfaces of the forms with
water.
Panel clamp
A bolt and wedge device ensures a tight fit
between frame panels.
Cold Weather
Lower temperatures cause concrete to
harden and gain strength more slowly,
hence a longer curing time is required to
reach specified strength.
21
certiWood™ Canply plywood Handbook
Centre section reinforced
Detail of clamp in place
Steel strapping
Lumber bracing is always necessary
because strapping alone will not support
plywood forms.
Detail of panel clamp
A typical 600 mm by 2400 mm metal framed
panel. One of the advantages of these
patented panel systems is that the framing
protects the plywood edges. The metal
frames themselves have a long life and the
plywood can be easily replaced or reversed.
Column Forms
Slab Forms
Pre-framed form panel
Plywood panel
Joists
Example of framing members supporting
plywood forms for concrete slabs. Concrete
may be poured on panels placed directly
over joists.
Preframed plywood panels may also be
used.
Miscellaneous Forms
Waler and tie rod
As tie rod does not adequately support the
plywood, this method is limited to columns
up to 300 mm square.
Plywood
19x89 mm stake
Double walers can be 38 mm by 89 mm, 38
mm by 140 mm, 38 mm by 184 mm or 89
mm by 89 mm.
Special steel column clamps are readily
available for column widths up to 1800 mm.
certiWood™ Canply plywood Handbook
38x89 mm
lumber
Concrete
Gravel
Smooth, curved concrete surfaces can be
readily obtained as plywood can be bent to
a very small radius, particularly when wet.
22
PLYWOOD IN FARM STRUCTURES
Arched Rafter Buildings
Farm Buildings
An arched rafter building should be
considered whenever an economic postfree, high ceiling building with a span in
excess of 18 m is required. Arches are
available for several custom fabricators in a
variety of engineered designs. This type of
structure derives its strength from the
combination of glue-laminated lumber
arches and plywood sheathing. Generally,
for spans under 12 m, the cost of an arch
rafter building is slightly higher than that of a
rigid frame building of comparable size.
Good farm buildings are the result of foresight, careful planning, and the correct use
of modern building materials. Changes in
agriculture in recent years have resulted in a
shift from conventional frame construction
for farm buildings to clear span structures
such as arched rafter, rigid frame, pole
frame, and trussed rafter buildings that are
designed for economy in construction,
efficiency in operation, and adaptability to
future requirements.
Gambrel Roof Arch Building
representatives, Provincial Departments of
Agriculture, agricultural research stations or
from Agriculture Canada, Ottawa.
PLYWOOD STRUCTURAL ASSEMBLIES
Stressed Skin Panels
An alternative to roof construction using
trusses and sheathing, stressed skin panels
create an open, unobstructed loft that can
be used for living and storage space.
Stressed skin panels are longitudinal
framing members (webs) covered on one or
both sides with CANPLY plywood flanges
(skins). The plywood is glued and nailed to
the webs so that the assembly functions as
an efficient structural unit.
Farm buildings sheathed with CANPLY
EXTERIOR
plywood
meet
these
requirements because they are easy to build
and can be closed in fast using readily
available materials.
The gambrel roof is a shape long associated
with the traditional North American barn.
This popular roof form constructed of four
lumber rafters connected by nailed plywood
gussets provides an aesthetically pleasing
clear span building using a minimum
number of lumber members.
These
buildings are used for conventional twostorey barn roofs as well as for single-storey
structures for storage of produce, grain or
machinery and in the wider spans are
popular for such uses as riding areas.
Plywood sheathing nailed to the frames
provides the necessary strength and
bracing to complete the building shell.
Stud Wall and Truss Buildings
Rigid Frame Buildings
Stud wall construction combined with
plywood gusseted trusses for the roof
system is generally considered most
suitable for heated, insulated livestock
buildings such as swine and poultry barns.
The bottom chords of trusses provide a
framework on which to attach the plywood
ceiling. This results in flat ceilings which
contribute to good air circulation and
ventilation. Stud walls are easy to insulate.
Ventilation equipment can be installed in the
walls, and air intakes can be readily
designed for walls or ceilings.
A rigid frame building is one of the most
Nailed plywood beams can be built easily
economical clear-span farm buildings
and quickly from CANPLY plywood and
available. Essentially, rigid frames are threeseasoned lumber. No special skills, tools,
hinged arches formed by four straight
materials or manufacturing facilities are
pieces of lumber joined at crown and
required. Beams can be fabricated in
haunches by nailed Douglas Fir plywood
workshops or at the job site.
gussets. Frames are usually spaced at 600
mm on centre and
When
assembled,
sheathed with CANPLY
nailed plywood beams
EXTERIOR plywood which
are light, strong, rigid
becomes an integral part of
and
ready
for
the structure and provides
immediate use without
stability and resistance to
the delays associated
racking. The substitution of
with lengthy glue-curing
periods typical of glued
other sheathing materials
beams.
Nailed
may endanger structural
plywood beams are
soundness. Rigid frame
Stressed Skin panels
suitable for a variety of
buildings are economical
interior
applications
for spans up to 12 m.
such as ridge beams in cabins and
Farm Buildings Plans
cottages, lintels in garages and carports,
and floor and roof beams in residential and
Plans for farm buildings are available from a
light commercial construction.
number of sources including retail lumber
dealers, building material manufacturers,
Design data is available from CertiWood™
and also in the design code CSA 086
Provincial Departments of Agriculture, and
Engineering Design in Wood.
contractors and consulting firms specializing
in farm building and design.
FINISHING
Some of the best and most comprehensive
Selection and Application of Finishes
plans were developed by the Canada Plan
Service, a co-ordinated program of the
Long life and enduring beauty of almost any
Federal and Provincial Departments of
wood depends upon protecting the surface
Agriculture across Canada. These plans
with a properly applied coating. Plywood
may be requested from agricultural
The great selection of economicallydesigned trusses now available adds
flexibility to such buildings. Wood trusses
are economical for all widths of farm
buildings up to 12 m and have been used for
spans to 20 m.
Pole Frame Buildings
Plywood sheathed pole frame buildings
have proven their worth as hay shelters,
open-front shelters, loose housing for diary
cattle, and machinery sheds. They are low
in cost, flexible in design, and easy to erect.
Since the poles provide stability to the
building, no expensive foundations are
necessary and the plywood roof and wall
sheathing nailed to the frame acts as a large
diaphragm, adding strength and rigidity to
the entire structure.
23
The panels are fastened to the floor structure
at the eaves and normally fastened together
at the ridge. Adjacent panels are lapped so
as to be self-supporting and provide a
smooth roof surface. No internal bracing is
required. Openings in the panels can be
framed during fabrication to accommodate
skylights or windows.
Design data is available from CertiWood™
and also in the design code CSA 086
Engineering Design in Wood.
Nailed Plywood Beams
certiWood™ Canply plywood Handbook
requires the same basic protection against
the elements.
The waterproof glue used in the
manufacture of CANPLY EXTERIOR
plywood will withstand exposure indefinitely,
but to assure maximum life and beauty of
the wood itself it is necessary to give close
attention to surface finishing techniques.
Procedures for finishing plywood differ little
from those used to finish other woods and a
variety of attractive finishes is possible for
both interior and exterior applications. There
is seldom one “best” finish that can be
recommended for plywood. Factors such
as the condition of the surface, the method
of the application, the conditions to be
encountered in service - probably the most
important factor - the service expected, and
the economics of initial cost versus
appearance and durability must be
considered.
This section describes some of the finishes
available for plywood and their methods of
application. It is extremely important that
care be taken in selecting the most suitable
finish for the purpose intended and applying
it according to the manufacturer’s
instructions. There is no better assurance of
satisfaction than the correct finish properly
applied.
Care and Storage
The importance of proper care and storage
of plywood prior to finishing cannot be overemphasized. Plywood which will become
part of the decorative scheme should be
handled as carefully as trim material, sidings
or other quality finish products. Many early
paint failures can be traced directly to
improper handling and storage. Moisture
can enter the panel prior to finishing during
storage in damp or humid areas, or because
of delay in priming the plywood after
installation, or because of omission of the
edge seal. (The latter two are important only
if the panels are to be exposed outdoors.)
Thus all panels should be stored in a cool,
dry place out of the sunlight. They should be
well covered if left outdoors during
construction. The prime coat and edge seal
for panels intended for exterior exposure
should be applied as soon as possible.
Water repellent coatings do not serve as a
substitute for the prime paint coat. They will,
however, retard moisture pickup until the
prime coat can be applied and,
providing they do not have a wax base,
should provide an improved surface for
painting.
Checking
Unprotected plywood exposed to the
weather may look unsightly in a few months.
This is not because the plywood itself
deteriorates but because of the tendency of
certiWood™ Canply plywood Handbook
the surface veneer to check; a phenomenon
common to all wood in which hundreds of
tiny hairline cracks open up parallel to the
face grain. These tiny cracks or checks are
caused by the wood fibres separating at the
growth boundaries as the fibres swell or
shrink as the result of rapid changes in
moisture content.
Checking has no
appreciable degrading effect on the strength
of plywood because plywood’s strength lies
predominately in the direction of the grain.
However, checking seriously mars the
appearance of the plywood, and once it has
occurred is difficult to hide with paint alone.
There are various products available under
proprietary brand names that are claimed to
be compounded especially to help plywood
resist checking and reduce grain raise.
These products can be applied by brush or
spray. Two coats are usually recommended.
They penetrate and seal the wood and
reportedly help stabilize the face veneer
against dimensional changes due to
moisture.
Where checking has occurred because of
improper storage, the panel surface must be
reconditioned before finishing to obtain the
best appearance and performance. This is
also true of old paint surfaces that have
deteriorated to the point of needing renewal.
Medium Density Overlaid plywood
(described on page 7) is not susceptible to
checking because of its resin-fibre overlay.
Exterior and Interior Edge Treatments
Exposed and concealed edges of plywood
in exterior applications should be sealed
with paint as described following. Exposed
panel edges should also be covered with
wood battens or moulding fastened with
corrosion-resistant nails.
Concealed edges of plywood in interior
applications need not be sealed. For
appearance, the end grain of exposed panel
edges can be hidden either with wood filler
applied to the edges and then sanded and
painted or with an edge trim of wood
moulding, wood veneer, or proprietary
clamp-on edging.
Joint Treatments
The tendency in recent years has been to
accentuate the joints between plywood
panels rather than trying to hide them. This
simplifies construction and can be quite
attractive. Most often these joints are made
by easing the edge of each panel with a 45
degree bevel, about 3 mm deep. Joists are
commonly accentuated in naturally finished
panels and frequently in painted panels.
Butted joints covered with battens or
moulding are also used to further emphasize
the panelizations.
24
Fastenings
On exterior walls and in excessively damp
locations, the type of fastener used to
secure the plywood to the framing has an
important bearing on the appearance and
durability of the finish. For long service and
freedom from rust staining, corrosionresistant fasteners should be used.
EXTERIOR FINISHES
Edge Sealing
All plywood edges, exposed or concealed,
should be sealed with one or more heavy
coats of exterior primer or aluminum-based
paint. This prevents moisture migration into
the edges. Edge sealing can readily be
done when the panels are in a stack. In very
damp locations, panel backs should be
primed with a coat of exterior primer.
Stain
A stain finish is ideal for unsanded plywood
panels exposed to the weather. A heavybodied stain is particularly recommended
and will provide an attractive finish requiring
little maintenance.
Stains are available which have
considerable hiding power but do not
obscure the plywood grain. Creosote base
stains penetrate deep into the plywood,
producing rich lively colours that enhance
grain beauty but leave little or no surface film
to crack and blister. Stains containing water
repellents are thought to be useful in
deferring checking.
Stains are among the easiest of finishes to
apply. The usual requirements for a clean
dry surface apply. Successive coats should
be allowed to dry before the next coat is
applied. One or two coat systems should be
used depending upon the manufacturer’s
recommendation and the pigmentation in
the stain (penetrating stains usually require
two coats). Since colour uniformity depends
upon equal pigment distribution, stains
should be thoroughly mixed before
application and from time to time during
application.
Checking in stained plywood usually occurs
during the first six months of outdoor
exposure. With heavily pigmented dark
stains, best results are obtained by applying
a first coat and allowing any checking to
occur, then six months or so later a second
coat can be applied so that the checks are
filled with stain. When the stain weathers or
fades so that refinishing is indicated, little or
no surface preparation is needed.
Pre-stained specialty plywood siding
products in a variety of colours are available
from some manufacturers.
Stain cannot be used successfully on
overlaid plywood. Sanded panels may be
stained if desired.
Paint
Paint is not recommended for application to
the standard grades of plywood used in
exposed locations. Under severe exposure
conditions, checking of the surface veneer
may cause paint deterioration. When a paint
finish is desired, the use of Medium Density
Overlaid (MDO) plywood is recommended.
This smooth, uniform surface provides an
excellent degree of adherence, allowing
paint resins to firmly grip the surface
resulting in excellent durability, exceeding
that of paint finishes on ordinary wood. Paint
flow is even and smooth, penetrating the
surface uniformly resulting in more attractive
appearance and more efficient paint use.
Painting recommendations are as follows:
Surface Preparation
Medium Density Overlaid plywood needs no
surface preparation. No pre-sanding or
sealer coats are required. However, it is
important that the surface has been allowed
to dry for at least 48 hours and is completely
clean before applying your first coat of paint.
Prime Coat
Any good primer, properly formulated and
designed for exterior exposure, may be used
with satisfactory results. The limitations may
be listed as follows:
1. Strict adherence to the
manufacturer’s recommendations.
paint
2. Compatibility of the prime coat to the top
coat must be considered. In this respect the
use of flexible film-forming primers, such as
some of the latex or oleoresinous base
formulations, are not recommended when
they are to be top coated with a hard filmforming primer over coated with a softer,
more flexible film-forming finish coat.
Top or Finish Coat
Nearly all good quality paints formulated for
exterior finish are acceptable as a top or
finish coat. As with the prime coat, the
manufacturer’s recommendations must be
followed and the compatibility of the top coat
to the primer must be considered. Check
before you paint!
With the advent of the many new synthetic
resins and their possible combinations , it is
almost impossible to evaluate all systems
and formulations relative to their
performance on Medium Density Overlaid
plywood. However, experience and testing
to date permits the following more specific
recommendations:
For exterior exposure such as in agricultural,
residential, marine and sign applications, the
best results have been obtained with self-
primed long or medium oil alkyd finishes
and enamels, vinyl alkyd enamels and
phenolic enamels applied over medium or
long oil alkyd primers.
Most latex paints of the styrene-butadiene,
acrylic and polyvinyl acetate emulsion type
have exhibited satisfactory results whether
self primed or applied over alkyd primers.
Systems not recommended are self primed
blister resistant titanium paints, polyvinyl
acetate homopolymer latexes, lacquers, and
paints containing zinc oxide.
If non-overlaid plywood has been used and
a paint rather than a stain finish is desired,
top quality exterior paint should be applied
as follows:
Prime the panels carefully front and back
with oil-base undercoat or aluminum-base
paint. If aluminum-base paint is used as a
primer ensure that it is of the type specified
for wood and not for general purposes or
metals. Ensure that the undercoat and
subsequent coats seal the edge grain. A
three coat finish with an intermediate coat of
undercoat (but not aluminum-base paint)
mixed half and half with finish colour will look
best. For the final coat apply the paint unthinned.
Low lustre and porous type paint systems
which permit the capillary flow of moisture
through the paint film should not be used
because the frequent wetting and drying of
the plywood surface will lead to abnormally
early checking and paint failure.
Refinishing Painted and Checked Plywood
A good repaint system for refinishing
checked plywood is an exterior acrylic latex
paint formulated for wood and applied in two
coats over a compatible oil-base primer.
Although some of the open checks may still
be visible, this flat finish tends to mask the
checks and presents a satisfactory
appearance.
Checks may reappear
because of moisture changes, but the paint
system will maintain its bond without
showing the typical curling and flaking of an
oil paint. The procedure is as follows:
1. Thoroughly wire brush the old paint
surface and sand if necessary to provide a
smooth surface for repainting. (If paint
deterioration is well advanced, it may be
advisable to remove all the flaking paint
down to the bare wood.) Old paint can also
be removed by liquid paint removers,
scraping or special paint removing tools.
2. Wipe off dust and excess chalk.
3. Apply a brush coat of oil-base primer.
4. When dry, apply two coats of acrylic
latex paint.
25
For better appearance and performance, the
open checks may be filled with any suitable
synthetic patching compound (a number of
which are available under specific brand
names) and the surface repainted with latex
paint as described above. The plywood
should be thoroughly dry to ensure that
existing checks are fully open to the filler. If
carefully applied, the compound will fill the
open checks and, after sanding, provide a
smooth, void free surface for repainting.
Plywood refinished by this method and
exposed to severe weather conditions will
eventually show some surface roughness as
the filler is forced out of the checks by the
repeated working of the fibres of the face
veneer, and paint failure may eventually
occur as a result of this movement.
Clear Finishes
Clear finishes for exterior exposure have
been found to be generally unsatisfactory
and are not recommenced for use on
plywood.
Clear coatings quickly fail
because of the lack of protective pigments
and thus require constant and costly
maintenance.
Textured Coatings
Proprietary surface coatings containing
fibrous or granular materials in a liquid
vehicle are available for use over plywood
and have proven more satisfactory for
exterior use than conventional paints. It is
claimed that certain types of textured
coatings are highly resistant to alkali and
acid conditions and are not susceptible to
the atmospheric conditions found in
industrial and coastal areas. Service life of
10 to 20 years is claimed for some types.
Coatings of this nature which conceal and
protect the plywood appear to be one of the
best methods of finishing plywood for
exterior exposure and their use is
recommended.
Overlays
There are many overlays and coatings
suitable for exterior use with plywood. Most
common are fibreglass and various
proprietary brands of synthetic membranes.
INTERIOR FINISHES
Surface Preparation
Plywood for interior applications will usually
be one of the sanded or textured grades and
will require little surface preparation other
than to ensure that the surface is thoroughly
clean and that all blemishes have been filled
with wood filler and sanded smooth.
Whenever practical, fill the plywood edge
grain before painting. Always use fine
sandpaper and sand with the grain, never
across it. Do not paint over dust or spots of
certiWood™ Canply plywood Handbook
oil or glue. When painting plywood, all knots
and pitch streaks should be spot-primed
with sealer. For best results use good quality
paints and follow the paint manufacturer’s
instructions.
decay can be increased by preservative
treatment, the annual cost of treated
plywood under these conditions could be
substantially below that of untreated
plywood.
Paint and Enamel
Conventional wall and woodwork paints and
enamels may be used. For surfaces which
will be cleaned frequently, use washable
paints or enamels. First, brush on flat paint
or enamel undercoat. Thin if desired.
Second, apply a second coat of undercoat
tinted to shade of finish coat. For gloss
finish mix equal parts flat undercoat and
gloss enamel for second coat. Third, apply
final coat as it comes from can. A two-step
finish without second undercoat may be
used as an alternative.
Interesting textured surfaces may be
obtained by priming as above, followed by a
heavy coat of stippling paint. Use brush,
roller or sponge to texture. When using
water-thinned paint, first seal plywood with
clear resin sealer, shellac or flat white oil
paint, then paint according to manufacturers’
instructions for a sealed surface.
Preservative Penetration and Retention
Plywood can be penetrated by preservatives
more readily than solid wood of the same
species. Rotary-cut veneer develops many
small fissures which flatten out in the press.
These minute cracks are hard to detect with
the naked eye but are readily penetrated by
preservative under pressure.
Plywood contains some end grain on all four
edges and end grain can be penetrated
much more easily than edge grain. This,
plus the lower moisture content of the
plywood, helps make the treatment uniform
throughout the thickness of the panel. Such
penetration means that plywood can be cut
after treatment without any loss of
preservative protection at the cut edge
although application of a field cut
preservative (available from treating
companies) for critical end uses is
recommended.
Various pressure treatments (differing mildly)
are available, but the general principle of
forcing a preservative solution into the
plywood under controlled vacuum, pressure
and temperature is common to all.
Preservative retention is generally specified
in terms of the weight of preservative per
cubic metre of wood treated. As plywood is
an absorptive product, it achieves required
retention standards more easily than sawn
lumber. Like lumber, the ability to accept
treatment varies with species.
For
permanent wood foundations where
treatment specifications are extremely strict,
wood foundation standards limit species
permitted for this end use. Only easily
treatable species are recommended.
Retention by plywood of creosote and
petroleum mixtures varies from 256 to 400
Retention of water-borne
kg/m3.
preservatives varies from 4 to 10 kg/m3 after
drying. Fire retardant treatments require a
retention of 48-80 kg/m3. The amount of
preservative retained in a water-borne
treatment as compared with an oil treatment
is less because the solvent is removed by
drying in the former, whereas both
preservative and solvent remain in the wood
in the latter. It should be noted that oil-based
preservatives will leach out over time thus
affecting the appearance of the plywood.
Natural Finishes
For an easy, inexpensive blonde finish, first
apply interior white undercoat thinned so
grain pattern shows through. Tint if colour is
desired. Second, apply clear shellac, flat
varnish or lacquer.
Attractive and economical one-coat stain
waxes are also available in various colours.
If a dark stain is preferred, first apply coat of
clear resin sealer to subdue grain contrast.
A luxurious light stain glaze can be obtained
as follows: First apply white undercoat
thinned with an equal part of paint thinner.
Wipe or dry brush for more grain show
through. Second, apply one coat thinned
white shellac or clear resin sealer. Third, to
provide colour, apply interior undercoat or
enamel thinned as in step one. Wipe or dry
brush to proper colour tone. Fourth, apply
one coat of flat varnish. Rub down with steel
wool for added lustre.
PRESERVATIVE TREATMENTS
For most construction uses plywood
requires no preservative protection other
than conventional finishes. However, when
plywood is to be exposed to adverse
conditions such as wood-decaying fungi,
marine borers or wood-destroying insects, it
should be treated with suitable wood
preservative.
The chemical treatment
creates a barrier which preserves the wood
from deterioration and protects it against
insect attack. Each veneer of the panel must
be penetrated by the chemical if the
protection is to maintain its integrity.
Preservatives applied by dip, brush or spray,
although useful in some circumstances, are
effective only over the short-term because
the treatment is superficial. The optimum
penetration and retention of the preservative
can be achieved only by pressure
impregnation.
Since the service life of plywood exposed to
certiWood™ Canply plywood Handbook
Exemption from Phytosanitary Regulations
Due to the extreme temperatures and
pressures during the manufacturing
process, CANPLY EXTERIOR plywood
has been accepted internationally under all
known phytosanitary regulations for the past
30 years. Agriculture Canada’s Food
Production and Inspection Branch
recognizes Canadian Softwood plywood
as a “processed product”, and therefore
deems phytosanitary certification unnecessary.
Wood packaging constructed of coniferous
materials originating from Canada, Japan,
26
China and the United States, destined for
European Union countries, are subject to
phytosanitary entry requirements. The
Canadian Food Inspection Agency has
developed the Canadian Wood Packaging
Certification Program (D-01-05), designed to
ensure wood packing manufacturers meet
these requirements. Under this program,
plywood is considered a “manufactured
wood” and is exempt from these import
regulations.
FIRE-RETARDANTS TREATMENTS AND
COATINGS
Under certain conditions wood members
are required by building and fire codes to
meet minimum standards of fire resistance
or flame spread. Where flame spread
requirements less than 150* are stipulated,
plywood must be treated to reduce flame
spread over the surface of the panel. There
are a number of treatments that have proved
successful in this regard, the two most
common being pressure impregnation with
water-borne salts and surface coating with
fire-retardant paints.
* Flame spread rating of DFP, CSP, Aspen or
Poplar plywood bonded with exterior type
glue. Rating derived in comparison with
uncoated red oak as 100.
Pressure Impregnation
Plywood impregnated with a fire-retardant
chemical is usually a proprietary brand
name product available only from pressure
treated companies. This type of treated
plywood, which requires a salt retention of
48 to 80 kg/m3 is effective as a fire-retardant
finish but it is generally restricted to interior
exposure because of the possibility that the
protective salts will leach out of the plywood
if exposed to the weather.
Some treatments may reduce panel
strength. Strength modification factors must
be determined by testing.
Surface Coatings
Fire-retardant surface coatings that reduce
the combustibility of plywood can be applied
by brush or spray wherever conventional
painting is possible. The reaction of these
coatings under the influence of flame and
the actual mechanism of protection varies
according to the composition of the coating.
Some of the basic mechanisms of
protection are as follows:
Insulation
In which thick coatings insulate the plywood
against high temperatures.
Crust Formation
In which coating melts under heat, covering
the plywood with an impermeable insulating
crust that prevents the release of
combustible gas from the plywood and at the
same time deprives the plywood of oxygen.
Heat Absorption
In which the coating absorbs the heat and
maintains the temperature of the protected
surface below its ignition point.
Table 16. Recommended applications of preservative Treated Canply EXTERIOR plywood
Exposure
Preservative Treatment
Typical Applications
Contact with sea water, exposed to
marine borer attack.
1. Creosote, 400 kg/m , full-cell.
2. Chromated copper arsenate, 40 kg/m3
3. Ammoniacal copper arsenate, 40 kg/m3
Box pontoons, wharf bulkheads, scows,
floats, flood gates.
Subject to severe insect and
fungus attack
1. Creosote, 400 kg/m3, empty or full-cell.
2. Chromated copper arsenate, 6.4 kg/m3
3. Ammoniacal copper arsenate, 6.4 kg/m3
Structures in tropical or semi-tropical areas
which use plywood in the form of
subflooring, roof and wall sheathing, interior
and exterior paneling and in structural
components such as beams and stressed
skin panel. Fences, permanent trench and
tunnel lining, septic tanks, retaining walls
and signs.
Contact with ground, fresh water,
chemicals, high humidities.
1. Creosote, 160 kg/m3, empty-cell.
2. Chromated copper arsenate, 6.4 kg/m3
3. Ammoniacal copper arsenate, 6.4 kg/m3
Permanent trench and tunnel lining, retaining
walls, cribbing, snow sheds, floats, irrigation
structures, tanks, troughs, plant boxes, lining
wet process industries, dropping trays
(poultry), septic tanks, some chemical storage
tanks, industrial sewers, smelter roofs.
Contact with chemicals and high
humidities or subject to insect or
fungus attack but not in contact
with wet ground or water.
1.
2.
3.
4.
5.
6.
Lining in buildings with humid conditions
dropping trays (poultry), exterior use where
poor ventilation is conducive to decay, signs,
marine installations and boat structures not
immersed in water, and outdoor uses
subject to repeated wetting and drying.
Contact with ground (wet or dry)
and subject to attack by insects
and decay organisms. Extra longterm performance required
1. Chromated copper arsenate, 9.6 kg/m3,
2. Ammoniacal copper arsenate, 9.6 kg/m3
3
Creosote, 96 kg/m3, empty-cell.
Acid copper chromate, 4 kg/m3
FCAP, 4 kg/m3, oxide basis
Chromated zinc chloride, 7.2 kg/m3, oxide basis
Chromated copper arsenate, 4 kg/m3, oxide basis
Ammoniacal copper arsenate, 4 kg/m3
Permanent wood foundation systems.
*For detailed specifications for the preservatives listed, see Canadian Standards Association Specification O80 Series.
For fire-retardant treatments, consult local treating company for specifications and recommended applications
Intumescent Insulation
In which the coating swells when heated to
form a thick insulation layer that delays the
spread of flame and heat transmission to the
protected surface. Intumescent coatings
are of the greatest commercial importance.
EFFECTS OF PRESERVATIVES AND FIRE
RETARDANTS ON THE STRENGTH OF
PLYWOOD
Acid salts have a hydrolytic effect on wood if
they are present in large concentrations.
However,
concentrations
used
in
preservative treatments of wood are
sufficiently small that the strength properties
are not greatly affected under normal use
conditions.
Under the provisions of
CSA O86 Engineering Design in Wood (Limit
States Design), no reduction in capacities
applies for preservative treated plywood for
plywood treated with other potentially
strength reducing chemicals, strength and
stiffness capacities shall be based on the
documental results of tests that take into
account the effects of fire, temperature and
moisture content. Tests show that plywood
treated with coaltar creosote and
preservative oils developed no reduction in
bond strength of the plywood. Similar tests
and experience have shown no adverse
effect on the durability of the bond strength
when CANPLY EXTERIOR waterproof glue
plywood is pressure treated with waterborne salts preservatives.
SPECIFYING PLYWOOD
Product Specification
To write a correct specification for plywood, the main points to consider are:
1.
2.
3.
4.
5.
Product Designation
Nominal Thickness
Manufacturing Standard
Grade
Additional Information (if necessary)
Example Specifications
Floor Sheathing
Product Designation:
Nominal Thickness:
Manufacturing Standard:
Grade:
CANPLY EXTERIOR EASY T&G Floor plywood
15.5 mm
CSA O151 CSP
Select Tight Face Cleaned and Sized
Roof Sheathing
Product Designation:
Nominal Thickness:
Manufacturing Standard:
Grade:
CANPLY EXTERIOR EASY T&G Roof plywood
12.5 mm
CSA O151 CSP
Sheathing
Concrete Formwork
Product Designation:
Nominal Thickness:
Manufacturing Standard:
Grade:
CANPLY EXTERIOR COFI FORM PLUS plywood
17.5 mm
CSA O121 DFP
Medium Density Overlaid - Two sides
Permanent Wood Fountations
Product Designation:
CANPLY EXTERIOR plywood
Nominal Thickness:
15.5 mm
Manufacturing Standard: CSA O151 CSP
Grade:
Sheathing
Additional Information:
Preservative treatment to CAN/CSA-080.15
27
certiWood™ Canply plywood Handbook
Why Plywood?
Simply because it outperforms all substitute wood-based panels on the market today.
Plywood is a highly stable panel. When exposed to moisture or high humidity,
plywood is up to seven times more resistant to thickness swell than
substitute wood-based panels. Plywood also returns to its original
dimensions when it dries.
Plywood is stronger than substitute wood-based panels in the four important
engineering strength properties of bending, tension, compression and planar
shear and plywood weighs up to 40% less than substitute wood-based panels
of equivalent thickness.
Plywood is a highly impact-resistant panel and continues to perform even
when wet.
735 West 15th Street
North Vancouver, BC
V7M 1T2
Tel: (604) 981-4190
Fax: (604) 981-4196
Toll Free: 1-866-981-4177
email: info@certiwood.com
Plywood has over 50 years of proven service as a structural panel for homes
and construction and remains, according to surveys, the panel of choice by
home buyers, contractors, architects and engineers.
Plywood is manufactured from logs averaging 10 inches in diameter from
managed sustainable forests. 100% of the log is utilized for either veneer, or
by-products, such as 2x4 lumber, landscaping ties or chips for pulp and paper.
Nothing is wasted.
Plywood manufacturing, because it is a value added process, employs four
times as many people compared to the manufacture of substitute wood-based
panels - using the same volume of logs.
Visit our Websites:
CANPLY: www.canply.org
CertiWoodTM: www.certiwood.com
The information contained herein is provided for general reference and not as a representation or statement of any standards or specifications referred to.
CertiWood™ does not warrant the accuracy of any information contained herein. Readers are advised to consult official sources for accurate and timely information applicable to specific circumstances. CertiWood™, its directors, officers, employees, contractors, servants and agents shall not be responsible or liable
for any claim, cause of action, loss, damage, expense, business interruption, injury or death due to any cause whatsoever or howsoever related to the information contained herein, including negligence, misrepresentation, or breach of any statutory or other duty of care on the part of CertiWood™, its directors, officers, employees, contractors, servants or agents.
© Copyright 2012
Printed in Canada
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