Plywood Classification and Grading

 Plywood Classification and Grading

There are two broad classes of plywood, each with its own grading system.

One class is known as construction and industrial. Plywoods in this class are used primarily for their strength and are rated by their exposure capability and the grade of veneer used on the face and back. Exposure capability may be interior or exterior, depending on the type of glue. Veneer grades may be N, A, B, C, or D. N grade has very few surface defects, while D grade may have numerous knots and splits. For example, plywood used for subflooring in a house is rated "Interior C-D". This means it has a C face with a D back, and the glue is suitable for use in protected locations. The inner plies of all construction and industrial plywood are made from grade C or D veneer, no matter what the rating.

The other class of plywood is known as hardwood and decorative. Plywoods in this class are used primarily for their appearance and are graded in descending order of resistance to moisture as Technical (Exterior), Type I (Exterior), Type II (Interior), and Type III (Interior). Their face veneers are virtually free of defects.

Sizes

Plywood sheets range in thickness from. 06 in (1.6 mm) to 3.0 in (76 mm). The most common thicknesses are in the 0.25 in (6.4 mm) to 0.75 in (19.0 mm) range. Although the core, the crossbands, and the face and back of a sheet of plywood may be made of different thickness veneers, the thickness of each must balance around the center. For example, the face and back must be of equal thickness. Likewise the top and bottom crossbands must be equal.

The most common size for plywood sheets used in building construction is 4 ft (1.2 m) wide by 8 ft (2.4 m) long. Other common widths are 3 ft (0.9 m) and 5 ft (1.5 m). Lengths vary from 8 ft (2.4 m) to 12 ft (3.6 m) in 1 ft (0.3 m) increments. Special applications like boat building may require larger sheets.