We have spent some time with plywood boats over the last several years, both vintage and new, and a common problem that we have had to address is cracks that can develop in the outer veneer of the plywood. When plywood is made, the wood fibers are stressed from their original shape to form flat veneers, and over time the wood dries out and the fibers shrink. Repeated wet-dry cycles and sun exposure also can cause damage to veneer protected only by paint or varnish. The cracks, also referred to as checking, can be very fine or larger fractures that form a rough surface. At worst, there can be voids where bits of veneer have chipped off.

Photographs by the authors

The fir plywood deck was showing every bit of its age, some 70 years. The area in front of the sander has been partially sanded, removing the high spots created by the checking of the top veneer.

Applications of epoxy, both straight and thickened with silica, have been very effective in repairing the plywood and preventing further checking. Epoxy has adhesive and sealing properties that are superior to those of paint. Applied to bare wood, epoxy stabilizes the grain and provides a protective barrier to water intrusion. It provides a solid base for subsequent applications of varnish or primer and paint. If the surface being restored is especially rough, as it can be with fir plywood, fairing compound can make it smooth.

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