Waterproof plywood is sold at various home improvement stores and is made to withstand common outdoor weather conditions such as rain and snow. The American Plywood Association assigns letter grades to various types of waterproof plywood, and grades include A, B, C and D. Plywood labeled with a combination of two letters such as AB means two wood panels are glued together and each side has a different grade.
Waterproof plywood has many uses, including boat construction and flooring. It can also be used for decorative purposes. Plywood quality corresponds to its letter grade, with A being of the highest quality. Defects found in waterproof plywood include cracks, edge gaps, splits and knots. Grades A and B have the least defects.
Plywood assigned a grade of C or D is still usable, but defects are more visible and sometimes require repair. Some waterproof plywood grades include the letter X, which indicates the presence of plywood glue that tends to hold up well under various moisture conditions. However, X-type glue is not weather or water resistant, which can negatively impact the durability of plywood that uses it. Duo-grade waterproof plywood panels that have one high-quality and one low-quality side are cost effective for projects in which only one side must be highly water resistant.