Plywood is a product made up of numerous thin strips of wood, known as veneers.
Each veneer sheet is laid on top of each other with the grain of each alternating sheet running in opposition direction and bonded with glue into a plywood sheet. This method of construction creates a very strong and versatile man-made timber material which is less susceptible to expansion and shrinkage.
The majority of plywood is made from an odd number of layers, called plies (typically 3, 5 or 7), with an equal number of plies on each side of the center ply.
One side of the plywood sheet is known as the “face” which is normally the side which would be seen in most applications and is generally the superior side. The other side is known as the “back” and is generally not as appealing and maybe rough. You can purchase plywood that has two goods sides for those applications where both sides of the sheet will be visible.
Plywood is available in various lengths, widths and thicknesses. Standard dimensions for length are 1800mm, 2400mm and 2700mm. Width is generally 1200mm. Sizing can be imperial (2440mm) or metric (2400mm).
Thicknesses are available from 3, 4, 6, 7, 9, 12, 15, 17, 18, 19, 20, 21, 25 and 28mm. Thicknesses vary between different manufacturers and products.
When specifying plywood the following information should be supplied:
- Type of Plywood
- Structural Rating (where required)
- Veneer Grade
- Glue Bond
- Treated or Untreated
There are four types of glue bond for plywood manufacture described in decreasing order of durability.
Type A – produced from a phenol formaldehyde resin which, sets permanently under controlled heat and pressure. It gives a permanent bond that will not deteriorate in heat or cold or under wet conditions. It is used for marine plywood, structural plywood and exterior plywood which has long term exposure to wet or damp conditions.
Type B – produced from melamine fortified urea formaldehyde resin (MUF) which sets under controlled heat and pressure. Type B is suitable for plywood involved in up to two years full exposure to the weather such as in formwork plywood or exterior doorskins.
Type C & Type D – produced from urea formaldehyde resin (UF) which sets under controlled heat and pressure. These are interior bonds which are not recommended for any purpose where exterior conditions are involved. Even for interior purposes, C & D should not be recommended for structural applications. For areas around sinks, vanities and laundry tubs, Type A bonded plywood should be used.
There are four main veneer qualities specified for plywood and these are:
A high quality appearance grade veneer suitable for clear finishing.
Textured exterior cladding Interior wall lining Interior ceiling lining Furniture & joinery
An appearance grade suitable for high quality paint finishing.
Furniture & joinery Concrete formwork Primary sheathing Signs Engineered components
A non-appearance grade with a solid surface. All imperfections such as knot holes or splits are filled.
Concrete formwork Gussets Roof decking Flooring Sub sheathing Bins, boxes & crates Stressed skin panels Hoardings
A non-appearance grade with permitted open imperfections. Limited number of knots and knot holes up to 75mm wide are permitted.
Structural components Beams & portals Roofing Bracing Utility buildings
Each stress grade is equally satisfactory for use in structural applications. The higher the stress grade, the thinner the plywood requirement will be to perform the same structural function.
The following table is a guide to the thicknesses and stress grades required for typical applications:
|Lining panels||3 – 15||N/A|
|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|
Ammoniacal Copper Quaternary – ACQ is a water based preservative that prevents decay from fungi and insects
- Used with veneers
- 100% take-up
Envelope – LOSP / CCA
- Not 100%
- Cut edges have to be chemically re-treated
|H2||Above Ground||Perigen||Termite||Veneer 100%|
|H3||Above Ground||Ruply / AQ||Anti-Rot / Termite||Veneer 100%|
|H3||Above Ground||LOSP / CCA||Anti-Rot / Termite||Envelope|
|H4||Ground Contact||CCA / ACQ||Anti-Rot / Termite||Envelope|
|H5||In Ground Contact||CCA||Anti-Rot / Termite||Envelope|
Perforation and Laser Cutting
Many panel products can be perforated with either holes or slots which allow the panels to be used in areas where sound attenuation is important. Areas where this may be applicable include internal ceiling and wall linings in schools, public halls, gymnasiums, offices and other commercial premises. Most panel products can be perforated with decorative timber veneers being the most common. A standard range of hole sizes and patterns allows specifiers to achieve their sound requirements for any given area.
Laser cutting allows the flexibility of design to come to the fore as each project can be custom designed. Laser cut panels can be used as room partitions and feature panels.