Exposure Ratings. - The grade/trademark stamp lists the exposure durability classification for plywood. There are two basic types or ratings: exterior and interim. The exterior type has a 100-percent waterproof glue line, and the interior type has a highly moisture-resistant glue line. However, panels can be manufactured in three exposure durability classifications: Exterior, Exposure 1, and Exposure 2.

Panels marked "Exterior" can be used where there is continual exposure to weather and moisture. Panels marked "Exposure 1" can withstand moisture during extended periods, but they should be used only indoors. Panels marked "Exposure 2" can be used in protected locations. They may be subjected to some water leakage or high humidity but generally should be protected from weather.

Most plywood is made with waterproof exterior glue. However, interior panels may be made with intermediate or interior glue.

Hardwood Plywood Grades

Hardwood plywood panels are primarily used for door skins, cabinets, and wall paneling. The Hardwood Plywood Manufacturers' Association has established a grading system with the following grades: premium (A), good grade (1), sound grade (2), utility grade (3), and backing grade (4). For example, an A-3 grade hardwood plywood would have a premium face and a utility back. A 1-1 grade would have a good face and a good back.

Figure 3-40.-Planing and squaring to dimensions.