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Unread 07-04-2008, 09:25 PM   #13
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Join Date: Nov 2003
Location: LaConner, Washington
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Plywood grades

Plywood veneers are graded into five levels, as follows:
A – Highest grade level. No knots or knotholes. Some patches allowed
B – Small round knots. Patches and round plugs allowed.
C Plugged - An improved C grade, found in Sturd-I-Floor and some of the better underlayments.
C – Small knots and knotholes allowed. Lowest grade allowed in Exterior rated type plywoods.
D - Larger knots and knotholes. Limited voids/pockets allowed in wall and roof sheathing panels. This grade is not allowed in Exterior rated panels. Furthermore, it should not be used under a tiled surface
Example: When two grades are used together as in AC , the panel has grade A veneers on the face, C grade on the backside.

If you are interested in more technical information, the APA (Americal Plywood Association) publishes many free documents on plywood. This one here provides a thorough discussions of the various grades. APA Panel Handbook & Grade Glossary
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