How to Choose Plywood

Plywood, untreated, survived the floods of Hurricane Katrina. That, all by itself, makes it a valuable building material. The water resistant glues for plywood were perfected in the 1930's when animal glues were replaced by more durable synthetic resins cured by microwaves. That's what saved the plywood when it was flooded. Plywood today is labeled as exposure 1, which can handle limited exposure to water or Exposure 2, which is suitable for dry locations. Here are some other things to consider when choosing plywood.

Instructions

1. Most plywood for home construction has three five, seven or nine plies. As glues have improved, three ply has been used for most built in and molded furniture. Five-ply is the most common plywood and usually specified for sub flooring, finish-flooring and sheathing. Seven and nine ply are used mostly for woodworking.

2. Choose plywood by grade. Plywood carries a two-letter rating of quality. It tell us the grade of the face side and the backside of the plywood. A-grade means a face free of knots; B and C-grades have limited blemishes; D-grade can have open holes. If you need plywood that is excellent on one side, ask for "A-C"; it has A on one side and C on the other. B-C plywood is considered furniture grade and has patches that look like footballs on the surfaces. A-B plywood is rarely available these days as it is now considered a specialty grade. You may run across C-D-X plywood. The X says the plywood is a exterior grade. The D side may have patches and show some cracks and may have open knot holes. T and G plywood is a select grade with a factory-machined tongue on one side and groove on the other. This plywood interlocks to spread loads across joints.

3. Get the right size. Plywood is sold usually as a 4 foot x 8 foot sheet in six thicknesses; 5/16 inch, 3/8 inch, 7/16 inch, 1/2 inch, 5/8 inch. You can also order 4-by-10 foot sheets for walls and 1 1/8 inch thickness for special floors. 3/8 inch plywood or 5/8 inch plywood is usually used for most houses.

4. Fasten plywood to other materials using polyurethane glues as they resist moisture and work well both inside and out. Construction adhesives are best for gluing and screwing plywood to joists to avoid squeaks.

5. Cutting plywood requires supporting the sheet on saw horses. Use a circular saw set to a depth that will just cut through the plywood and cut with the best side down, so the veneer won't be damaged.