Plywood is classified by type as INTERIOR or EXTERIOR. Made of high-quality veneers and more durable adhesives, exterior plywood is better than interior at withstanding exposure to the elements. Even when wetted and dried

repeatedly or otherwise subjected to the weather, exterior plywood retains its glue bond and withstands exposure to the elements. Interior plywood can withstand an occasional wetting but not permanent exposure to the elements.

The several grades within each type of plywood are determined by the grade of the veneer (N, A, B, C, or D) used for the face and back of the panel (fig. 6-6). Panel grades are generally designated by the kind of glue and by the veneer grade on the back and face. Grading is based on the number of defects, such as knotholes, pitch pockets, splits, discolorations, and patches, in each face of the plywood panel.