Boatbuilding Plywood Specifications

From Glen-L's "Boatbuilders Notebook"

From Glen-L’s Boatbuilders Notebook.

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U.S. MARINE GRADE PLYWOOD

Third party quality assurance of plywood made in the U.S. is largely provided by APA. Manufacturers within the association produce plywood in accordance with recognized product standards and abide by APA quality assurance policies. Their plywood is identified with an APA trademark.

Marine-grade plywood is made entirely of Douglas-fir or Western Larch. The grade of all plies of veneer is B or better. B-grade veneer may have knots but no knotholes. A-grade veneer has no knots or knotholes. Both A and B grade may contain wood or synthetic patches. Panels are sanded on both faces or have a Medium Density Overlay (MDO*) or High Density Overlay (HDO*). The maximum core-gap size permitted is 1/8 inch. Its exposure durability rating is EXTERIOR and the glue used is a fully waterproof structural adhesive. It is considered a “premium” panel grade for use in situations where these characteristics are required. It is typically available in 4x8 foot sheets of 1/4, 3/8, 1/2, 5/8 and 3/4 inch thickness. Sheets up to 5x12 feet may be available. Available grades are A-A, A-B, B-B (face-back), MDO and HDO.

Marine-grade plywood is not treated with any chemicals to enhance its resistance to decay. If decay is a concern, it should be pressure-preservative treated to an appropriate standard.

The detailed description of veneer grades and Marine-grade plywood is contained in Voluntary Product Standard PS 1-07 Structural Plywood.