Plywood

Plywood is an assemblage of wood veneers bonded together to produce a flat sheet. An extremely versatile product, plywood is used for a wide range of structural, interior and exterior applications - from formwork through to internal paneling.

Overview

Plywood is an assemblage of wood veneers bonded together to produce a flat sheet. While it can be tailored to suit an extensive range of applications, the normal product consists of at least 3 plies, with the grain in the alternate plies running at right angles.

There are four groupings of plywood products, with each group designed for specific applications:

  • Structural 
  • Exterior
  • Interior
  • Marine.

Plywood offers the following benefits:

Increased stability
Plywood offers all the inherent advantages of the parent wood plus enhanced properties in its laminated structure.

High impact resistance
Being a wood based material, plywood has the ability to accommodate the occasional short-term overload; up to twice the design load. This is useful where seismic activity or cyclonic winds can occur. This property is also effective when used as construction flooring or as concrete formwork. Plywood's laminated structure distributes loads from impact over a larger area on the opposite face, which effectively reduces the tensile stress.

Surface dimensional stability
The cross laminated construction of plywood ensures that plywood sheets remain relatively stable under changes of temperature and moisture. This is especially important in flooring and formwork construction where moisture exposure is very likely.

High strength to weight ratio
With high strength and stiffness to weight ratios, plywood is very cost effective to use in structural applications such as flooring, shearwalls, formwork and webbed beams.

Panel shear
The panel shear of plywood is nearly double that of solid timber due its cross laminated structure. This makes plywood a highly effective material to use in gussets for portal frames, webs of fabricated beams and as bracing panels.

Chemical resistance
Plywood does not corrode and can be used in chemical works and cooling towers as a cost-effective, durable material when preservative treated.

 

Properties

Durability

The durability of plywood will in part depend on the bond quality used in manufacturing. Although the use of a durable adhesive provides a bond of long-term effectiveness, it does not guarantee that the veneers being bonded together will have any long-term durability. See Plywood - Adhesives in the Description tab.

For example, if plywood is to be used for a marine craft and will experience service conditions that encourage decay, then it will also be necessary to ensure that the veneers are of a durable species or that the plywood be preservative treated to the appropriate hazard level.

As structural plywood is manufactured from a range of hardwood and softwood species, it may not be durable in exposed weather situations so must be preservative treated to ensure its full service life can be reached.

Plywood is not recommended for fully exposed horizontal applications like decking because severe checking will occur, but it is a good substrate for membranes in this application. Face veneers are also prone to checking if left unprotected in adverse conditions.

Sizes

Plywood is available in several lengths, widths and thicknesses and this will be determined by individual suppliers.

Standard plywood panels are:
Length: 2700, 2400 and 1800 mm
Width: 1200 mm.

Standard plywood panel thicknesses are available in 3, 4, 4.5, 6, 7, 12, 13, 15, 17, 19, 21, 25 and 28 mm.

When specifying plywood (structural) the following information should be supplied:
-The number of panels x thickness (mm) x width (mm) x thickness (mm) 
-Plywood type and standard
-Stress grade and ID code (for structural plywood), 
-Face and back grades and the glue bond type, 
-EWPAA certification and preservative treatment if required

eg 20 sheets of 2400 x 1200 x 17 mm, T&G, Structural plywood to AS/NZS 2269
F11 (17-24-7)
CD - A bond
EWPAA Product Certified

Appearance plywood
Appearance plywood is specified by the required characteristics of the face veneers - species, colour, grain; and by thickness, lamination pattern, type (durability) of glue bond and any treatment.

Table - Typical structural plywood thicknesses and stress grades for common applications

Applications

Thicknesses (mm)

Stress Grade

Residential Flooring

13, 15, 17

F11,F14

Industrial Flooring

17-25+

F11-F22

Diaphragms

9-15

F11,F14

Bracing (Shearwalls)

3-15

F11,F14,F27

Box-beams

7-12

F11,F14

Portal frame gussets

12-25

F11,F14

Grades

Stress Grades

Stress grades are only applied to structural plywood. No stress grades can be applied to internal or external plywood as they are not designed to be used for structural applications.

Structural plywood engineering properties are given for eight standard stress grades. The characteristic strength and stiffness values of structural plywood are allocated via the F- grade classification system:

F7, F8, F11, F14, F17, F22, F27 and F34.

It should be noted that although the F-Grade characteristic strength and stiffness values of structural plywood and structural timber are the same for bending, tension, compression and modulus of elasticity; shear capacity of structural plywood is superior and Modulus of Rigidity is marginally reduced.

Appearance Grades

Plywood face grades

The face, or outside veneer, is available in 4 standard grades:

A Grade - a high quality appearance grade for clear finishing. 
Note: Marine plywood is only available with an A face both sides (A-A)

B Grade - designed to be painted. It provides a suitable substrate for high quality painted finished.

C Grade - a non-appearance grade which features some surface defects, filled during manufacture. Substrate required for all flooring, industrial shelving.

D Grade - this grade has open defects and is appropriate for surfaces to be covered, eg bracing/sheathing.

S Grade - a sliced cut decorative face for interior plywood. This is a non-standard product.

For a clear finished aesthetic application requiring one good surface, AD grade would be used. Structural plywood will usually have C or D grade faces, but higher quality face veneers can also be used.

Regulations / Standards & Codes

The Engineered Wood Products Association of Australasia (EWPAA), formerly Plywood Association of Australia, has operated a quality assurance program since 1963. This ensures that the plywood manufactured by mills participating in the scheme conforms to the relevant Australian Standard.

EWPAA members manufacture plywood to the following Australian Standards under an industry wide total product certification scheme:

AS/NZS 2269 Plywood - Structural
AS/NZS 2270 Plywood and Blockboard for Interior Use
AS/NZS 2271 Plywood and Blockboard for Exterior Use
AS/NZS 2272 Plywood - Marine
AS 6669 Plywood Formwork

The following standards are used in relation to sampling and testing:

AS/NZS 2097 Methods of Sampling Veneer and Plywood
AS/NZS 2098 Parts 1 to 8 Methods of test for Veneer and Plywood
AS/NZS 2098 Parts 11 Determination of Formaldehyde Emissions for Plywood
AS 2754.1 Adhesives for Plywood Manufacture
AS/NZS 2269.1 Structural Plywood - Determination of Structural Products

The following standards are applicable to structural plywood:

AS 1684 Residential Timber-Framed Construction Code
AS 1720.1 Timber Structures Code
AS 3610 Formwork for Concrete


*Disclaimer : The species mentioned here are just a guide and for specific information refer to Suppliers Section

Description

Material Sub Type

Structural plywood suitable for use in all permanent structural applications. It can be manufactured from a range of softwood and hardwood species and can be used for a range of structural applications including formwork, flooring, bracing and manufactured beams.

Internal plywood - for use in non-structural interior applications not subject to load, where a high quality aesthetic finish is required. Applications include internal wall paneling, furniture, ceiling linings and interior door skins.

External plywood - is intended for use in non-structural, exterior applications not subject to load, where a high quality aesthetic finish is required. Applications include exterior door skins, hoarding, signs and non-structural cladding.

Marine plywood - a purpose-built structural plywood intended for hulls of boats and yachts and other marine applications. It is also used in aircraft construction. Marine plywood always uses a Type A grade on both faces, which helps to minimize water penetration, and uses a Type A adhesive bond.

Fire Resistance

Fire resistance in the form of a fire rating can only be applied to a total building element incorporating plywood, eg a fire door or a wall or a roof system. A product can not be fire rated.

Plywood is acceptable as a material used in fire resistance components or structures, providing it is combined with other materials to meet the fire resistance requirements. This can be achieved chemically, however the usual method is to combine plywood with non-combustible materials such as fibrous-cement or fire grade plasterboard.

For more information about fire resistance regulations please refer to C1.10 Fire Hazard Properties within the Building Code of Australia (BCA).

Adhesives

Plywood is manufactured using four gluelines: A, B, C and D. The four types of bond quality are defined in AS2754.1. The appropriate type bond must be matched to the application and service conditions.

The bond quality of each is as follows:

Type A Bond - is a permanent bond required for all structural and marine plywoods. Using a phenolic resin-based adhesive, it is recognisable by its black colour, which will not deteriorate under wet conditions, heat or cold. It is also used in areas around sinks, vanity units and laundry tubs. Marine plywood always uses a Type A bond.

Type B Bond - is appropriate for a maximum of two years' exposure for applications such as formwork or for semi-exposed external door skins. It uses a Melamine Fortified Urea Formaldehyde resin.

Type C Bond (interior, non-structural) - is suitable for non-structural interior applications, or tropical locations with high humidity free from wet or damp conditions. Recognisable by its light glueline colour, it uses a Low Extension Urea Formaldehyde and is for interior bonds only.

Type D Bond (interior, non-structural) - is appropriate for non-structural internal low-humidity environments such as internal paneling. It uses a High Extension Urea Formaldehyde and like a Type C bond, its glueline is also light in colour.

Note: The term ‘waterproof plywood' doesn't necessarily mean that the plywood is waterproof but rather that the glue is waterproof.

Treatments

A range of preservative treatments are available for plywood including CCA (copper chrome arsenate) , LOSPs (light organic solvent preservatives) and for veneers, Ruply and ACQ (Alkaline Copper Quaternary Compounds).

For building construction the most suitable treatments are Copper Chromium Arsenic (CCA) and Light Organic Solvent Preservative (LOSP).

Plywood with a Type A bond used as exterior cladding must be treated against fungal and insect attack. This should be with a minimum of hazard level H3 for 'outdoors above ground' as per AS/NZS 1604.3.

Most softwood species can be treated with non-leachable preservative salts, which will impart decay resistance. The level of preservative treatment specified for softwood laminated beams used in Service Class 3 applications should be H3. Similarly LOSP envelope treatment can be used satisfactorily. Check with manufacturer for recommended use.

Protecting plywood
Plywood may be subject to decay and/or termite attack under certain conditions. In-ground applications can cause both decay conditions and termite attack. Correct preservative treatment against fungal attack (rot) is essential for all plywood, either painted or unpainted, that is to be permanently exposed to the weather. Infestation with termites is usually not a problem for plywood when used in above ground applications.

Plywood can be treated as follows:

  • Impregnation of veneers, prior to manufacture.
  • Pressure treating of the manufactured plywood - pressure treating plywood is an 'envelope treatment' only, treating the outer veneers, edges and ends of sheet. The preservative may not penetrate through the glue lines to the middle veneers. If plywood is cut, then localised paint on preservative treatment is required to the cut edge. This treatment is only practical for thicker panels.
  • Preservation treating surfaces after manufacture - preservative treated plywood is suitable for painting provided manufacturers recommendations are followed. Preservative treating after manufacture or surface treating with 'brush on' preservatives should be done only after machining, sawing and boring has been completed.

Some preservation treated plywood is difficult to bond, particularly with phenolic or resorcinol adhesives.

Design/Engineering Considerations

Curving plywood
Plywood can be curved for use in ceilings and feature walls.

Acoustics and sound insulation
Plywood is an excellent reflector of sound. A double‐sided plywood partition can reduce the noise levels by around 35 decibels.

Thermal properties
Plywood, when used in timber construction, provides a low thermal mass, making it an effective material for use in tropical or subtropical climates. For cooler climates, the addition of insulation can provide an equivalent thermal insulation to solid construction.

Table  - Characteristic strengths and elastic modulii for structural plywood (MPa): 

Stress Grade

Stress Value

Bending
f'b

Tension
f't

Shear
f's

Compression in the
plane of the sheet
f'c

Bearing normal
to the plane of the sheet
f'p

Modulus of Elasticity
E

Modulus of Rigidity
G

F34

100

60

6.8

75

31

21,500

1075

F27

80

50

6.8

60

27

18,500

925

F22

65

40

6.8

50

23

16,000

800

F17

50

30

6.8

40

20

14,000

700

F14

40

25

6.1

30

15

12,000

625

F11

35

20

5.3

25

12

10,500

525

F8

25

15

4.7

20

9.7

9,100

455

F7

20

12

4.2

15

7.7

7,900

395

Note: F11 and F14 are the most common grades available.

Table  - Average percentage movement of structural plywood per percent change in moisture content:

Direction of Movement

Moisture Content Range %

5%-12%

12%-17%

17% - Saturation

Average 5% - Saturation

Along the face grain

0.017

0.009

0.005

0.011

Across the face grain

0.021

0.010

0.008

0.013

Note: The values are the averages for a thickness range of 12 - 22 mm

 

Handling, Storage & Protection

Structural plywood requires care in storage and handling:

  • The storage area should be protected from sun, rain and wind that cause any rapid changes in temperature and humidity. To avoid staining, fading and surface checking, the sheets should not be exposed to the weather while awaiting installation.
  • Support for the sheets should be provided at both ends and at 600mm intermediate centres to avoid distortion.
  • The stack should be kept dry and clear of ground contact, and be placed so that it will not be exposed to mechanical damage.
  • The sheets should be stacked on their flat, NOT on edge.

Cutting Holes & Notches

Plywood can be sawn, and drilled using regular carpenter's tools.

The placement of notches and holes in particular plywood elements may be restricted in size and location to maintain the structural integrity of the plywood element.

For example, tradespeople may need to make penetrations through plywood bracing panels. A neat hole (ie not overcut) of up to 100 mm x 100 mm within an envelope of 100 mm from the vertical and top edges and 200 mm of the bottom edge of the bracing panel will have no significant effect on the bracing capacity. Multiple 100 mm x 100 mm holes are allowable within the envelope, but their centres must be no closer than 600 mm.

Advice should be sought from the plywood manufacturer or the Engineered Wood Products Association of Australasia (EWPAA), as to the permitted location and size of holes.

Maintenance

Ongoing maintenance and inspections will help to make sure rot/infestation does not occur in structural above-ground applications.

Workability

Plywood can be sawn, drilled, screwed, nailed with ordinary woodworking tools.

Because manufactured wood products are based on timber, they have the same practical workability attributes as solid structural timber. However, in some cases construction practices need to be modified to fit the requirements of the various product characteristics.

Another advantage of working with plywood is its flexibility. Bending and moulding plywood is relatively simple. Plywoods with Type A bond phenolic gluelines can be soaked or steamed to assist bending.

Plywood is generally a very stable product however warping, bowing and twisting can occur due to moisture imbalances, unbalanced laminates, paint coats or unbalanced stresses.

Joints & Connectors

Fixing requirements for plywood are dependent on the application it is being used for. Plywood (structural) can be utilised very effectively as bracing, webs as well as gussets in portal frame construction.

The cross laminated structure of plywood allows close edge fixing.

It is important the type, size, number and spacing of fasteners is strictly in accordance with that specified or noted on the details for the particular application. Mechanical fasteners should not be over-driven as this will reduce the effectiveness of the fastener in transferring the loads from the plywood to the support framing or vice versa.

Edge distances should not be less than that specified for the particular application, however as a guide, minimum edge fastening distances are 7 mm for plywoods up to 7 mm thick and 10 mm from the edge for thicker plywoods.

For some applications, a glued and nailed (or screwed) joint can be more efficient. Glued connections have greater stiffness and can transfer load with less slip. However, the reliability of mechanical fasteners (nails and screws) gives assurance that connections using both glue and nails or screws will give long-term structural performance.

Fasteners used with preservative treated plywood should be hot dipped galvanised or have equivalent corrosion protection. Stainless fasteners may be required for severe exposure applications. Fasteners must be compatible with preservative salts (when treated against fungal attacks).

For more information, visit the Applications section

Finishes

All fully exposed plywoods must be surface finished to prevent surface checking or cracking. This is caused by the absorption and loss of moisture through the surface veneer.

ALL plywood used in externally exposed conditions must be Type A bonded and preservative treated to ensure long-term durability and performance.

Structural plywood
Needs to be surface finished to minimise surface checking if used externally. Structural plywood used internally does not require a surface finish.

Exterior plywood
May be finished by:

  • Painting 
  • Coating with water repellents
  • Overlaying with medium density phenolic impregnated papers.

Note: While not mandatory, edge sealing is considered good practice as it minimises moisture uptake. Horizontal surfaces for exterior plywood present a greater hazard to paint breakdown and surface checking than vertical surfaces.

Plywoods with an A or B grade face veneer quality provide a suitable substrate for a high quality paint or stain finish, but NOT C or D quality.

Plywood cladding products can be good for painting or staining as well as disguising surface checking of the veneer. Sanded surfaces, clear of defects are most suitable for painting.100% acrylic latex paint systems perform best on plywood. Oil based and alkyd enamel paint systems are not recommended for use on plywood in weather-exposed applications.

For natural looks, exterior water repellent stains are recommended. Medium density overlaid plywoods may be painted with a range of oil and water based paint systems

Interior Plywood
Clear finishing, French polishing, staining and painting of plywood are all options for interior plywood [but follow paint manufacturer's directions]

Before finishing, ensure the plywood is dry (below 12 - 15% moisture content) and the surface to be painted is clean, smooth and wax free.

A and B quality face veneers, when appropriately sanded, have a surface for high quality finishes, stains and paints. A is suitable for clear finishing, B is suitable for painting and under normal interior use C or D glue bonded plywood will give long term durability and preservative treatment is not necessary.

Stain and matt finishes and paints give a high quality aesthetically pleasing surface and are recommended, as they are more uniform with timber's characteristics.

Avoid high gloss finishes and paints as they will highlight beat marks from sanding, knots, grain variations, patches and open defects.

Overlaid plywood
Plywood can be overlaid with a range of materials to help protect against weather, wear and abrasion:

High Density Overlays (HDO)
This is a high density Phenolic resin impregnated paper overlay used in concrete formwork. It provides considerable face veneer protection as well as smoothness to the poured concrete surface.

Medium Density Overlays (MDO)
Provides an excellent paint surface and eliminates surface checking for exterior applications. Usually consists of a layer of Phenolic resin impregnated fibrous paper.

Metal overlays
Could include aluminium, copper and steel. This is a highly specialised job performed under strict quality control conditions.

Fibreglass overlays
Can be used for shipping containers, liquid storage tanks, bin linings and waterproofing.

Lead filled plywood
A composite plywood product used for soundproofing or as radiation protection.

Fibre cement sheet overlays
Used in some building applications for fire resistance.

Decorative overlays - see Decorative Veneers 

Applications

  • Doors

    Timber is one of the most popular and superior material choices for both internal and external doors. Whether manufactured from solid or engineered timber, there are many stylish and practical options that won't compromise on strength and structural performance. A distinctive timber door can also create visual impact, adding value to any commercial or domestic building.

  • Exterior Stairs

    For outdoor applications, timber is one of the leading material choices. Timber use in external staircase applications creates structures of strength and durability, sheathed in a natural beauty that blends seamlessly with the outdoor environment.

  • External Cladding

    The natural appeal, versatility and strength of timber makes it the superior choice for external cladding. Through specification, planning, design and finishing processes, timber cladding not only creates a building of superior strength, acoustic and thermal performance but also creates a place of beauty, style and natural appeal.

  • Flooring

    Whether for structural or finished flooring applications, timber offers durability, versatility and adaptability. The warmth, strength and natural beauty of timber flooring has proved enduringly popular in a wide variety of interior settings.

  • Framing

    Since people began building simple shelters, wooden framing has played an important role in shaping structures of many kinds. One of the most popular types of wooden framing is known as lightweight timber construction.

  • Interior Rails and Balustrades

    With its natural beauty and inherent strength, timber is a popular material choice in internal balustrade construction. Commonly built from treated softwoods and durable hardwoods, interior balustrades and handrails are typically finished with a clear lacquer to generate the most natural result.

  • Interior Stairs

    Timber should be the material of choice for designers seeking internal staircases of strength, beauty and durability. The construction procedure described here applies to most general type stairs of either conventional or contemporary construction.

  • Internal Paneling

    Timber paneling creates interiors as warm as they are stylish. Commonly utilising an MDF or plywood substrate, internal timber paneling is natural and versatile and comes as either solid natural timber panels or as sheets of engineered wood products

  • Shear walls

    Lateral loads such as wind or earthquake on framed timber buildings - either post and beam or stud and joist - need to be resisted and shear walls and diaphragms offer an effective and economical solution.

  • Timber Joinery Products

    Timber joinery products offer a classic, unique and stylish touch to any interior design.

  • Timber Portal Frames

    For buildings that require large spans and column free interiors, timber portal frames provide one of the most aesthetically pleasing solutions. Utilising modern engineering technology, portal frame design transforms timber into a highly effective, efficient and economical structural product. This application guide provides a comprehensive overview of the process of using timber in the specification, fabrication and erection of portal frame structures.

Case Studies

  • ARkit Prefab and Prefabricated Eco Homes

    Prefab and Prefabricated Eco Homes Australia: ARkit’s timber kit homes change the way we think about sustainable building and living.

    Applications : Decking, External Cladding, Flooring, Framing, Internal Paneling, Windows,

  • Australian School of Fine Furniture

    Expressing the traditional craftsmanship associated with bespoke furniture design, with a modern architectural twist, this new educational structure employs timber in unusual and unexpected ways.

    Applications : Architectural Roof Trusses, Decking, Flooring, Framing, Internal Paneling, Structural Timber Poles,

  • Community Facilities, Kensington Gardens

    An award-winning building where timber is featured to spectacular effect as well as adding the warmth and character that make residents feel at home.

    Applications : Architectural Roof Trusses, Flooring, Internal Paneling,

  • Cranbourne Botanic Gardens Visitor Centre

    The new Visitor Centre in the Australian Garden of the Royal Botanic Gardens, Cranbourne becomes a model of sustainable design the public can apply at home.

    Applications : Decking, Doors, External Cladding, Framing, Windows,

  • Joy Yeo Performing Arts Centre, Roseville College

    In Roseville College's Joy Yeo Performing Arts Centre, the use of Jarrah and Rose Gum pleases the ear as well as the eye.

    Applications : Flooring, Internal Paneling,

  • Letterbox House, Blairgowrie

    A holiday home that uses a range of commercial timber products and salvaged on-site timber to award winning effect.

    Applications : Architectural Roof Trusses, Doors, External Cladding, Fencing, Flooring, Framing, Windows,

  • Lewis St House, Thornbury

    A stunning residential renovation and addition that uses timber and timber products throughout with a commitment to sustainable design.

    Applications : Architectural Roof Trusses, Doors, External Cladding, Flooring, Framing, Interior Stairs, Windows,

  • NMIT Arts & Media Building, New Zealand

    A world first for its innovative use of LVL in the structure of a multi‐storey building, the NMIT building also incorporates a new generation of earthquake-­resistant engineering technology.

    Applications : Doors, Framing, Interior Stairs, Internal Paneling, Shear walls, Structural Timber Poles,

  • Peninsula Hot Springs

    At the Peninsula Hot Springs Gregory Burgess Architects use timber to create environments that enhance the spirit.

    Applications : Decking, External Cladding, Flooring, Framing, Interior Stairs, Structural Timber Poles,

  • Svarmisk Resort Centre, Mt Beauty

    A striking eco-resort that embodies the essence of new and recycled timber working together to form a unique, innovative and sustainable development.

    Applications : External Cladding, Flooring, Framing, Interior Rails and Balustrades, Interior Stairs, Internal Paneling, Pergolas, Shear walls, Structural Timber Poles,

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