The majority of plywoods used come from abroad. Bonding constructional veneers together face to face making sure the grains run in alternative directions make up sheets of plywood. Sheets are bonded on both sides of the original piece in order to keep the tensions equal. The basic number required is therefore three sheets, which is known as 3-ply. By adding another sheet to both sides, a stronger ply is produced, known as 5-ply. Using the same technique ply is available as 11-ply or higher. Ply will always be associated with odd numbers due to the process of equalising both sides of the original piece. By keeping to this procedure, possible warping is reduced. It is still possible to have warping or twisting, as every sheet of veneer is not completely identical to its equalised sheet. Another reason for warping could be due to water penetration or heat.
There are different types of plywood available, including standard, plastic faced and wood faced. If the wood is for external use, buy a more expensive ply laminate that is waterproof - exterior WBP (Weather and Boil Proof) graded. This means that the adhesives used in its construction are waterproof. There is another waterproof type on the market known as marine plywood that is also suitable for exterior use. Plywood can be used for many jobs in the same way as solid wood. It is stronger but more expensive than chipboard, and often has a more attractive surface, which can be either varnished or painted.
When storing plywood, always keep the sheets flat to avoid twisting. The sheets are available in numerous thicknesses including 4mm, 6mm, 9mm, 12mm, 18mm. WPB plywood sheeting is often slightly thicker, for example available in 9.5mm, 12.5mm and 18.5mm.
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