Plywoods for Special Jobs
If the finished piece is to be used outside or in damp conditions, you will need ply laminated with a waterproof bond. Ask for Exterior WBP, which is waterproof and boilproof. For boat-building, you need marine ply, specification BS 1088; for shuttering, use WBP ply with a phenolic resin coating.
Face veneered ply
Plywood is available in a number of thicknesses, with decorativeface veneers. Plastic-laminated plywood (the best known is Beautyboard) is available.
Most plywood is imported, and the more common types are: birch, Gaboon and West African mahogany, beech, Parana pine and Douglas fir.
Birch ply. One of the strongest ply-woods, it has a tendency to twist if poorly stacked, and is then difficult to straighten. Birch ply should not be exposed to damp unless it is a WBP grade. The edges will clean up well if you use a plane, followed by abrasive paper. The 3 and 4 mm thicknesses are very common materials for drawer bottoms.
Gaboon and West African ply. Lighter and weaker than birch, they have less tendency to twist. When resin-bonded they can be used satisfactorily outdoors. Commonly used in furniture-making, but the edge is difficult to finish. Cresta, one of the most popular branded makes, is available in different qualities for indoor and outdoor work (with proofing against insects), or with combinations of these qualities.
Beech ply. A very tough ply, which twists unless stored flat or held in position by rails when made up into furniture.
Resin-impregnated varieties are stable and extremely hard.
Parana pine. Quite hard, and takes a good finish, but it will wind in a corkscrew action if it starts to move. Not usually waterproof, and rots easily.
Douglas fir. Most commonly used for facing concrete and, in the thin sheets, 6-9 mm thick, mounted on battens as wall panelling. The grain darkens when it is exposed. End grain is rather coarse and not easy to finish.