By sealing these seams, moisture, insects, dust and air can't permeate into a home. Since it’s the ideal wood for moist or wet conditions, it’s often used to craft boats, boat parts, or outdoor furniture in coastal areas. Plywood used as a subfloor, wall underlayment or roof sheathing needs to have the seams sealed with caulk. On a new boat, with pristine seams between the planks, it is pretty straight forward. But total encapsulation is the key - that means enough coats to form an effective barrier, including all the sharp edges and bolt holes, etc. Jolt epoxy with glue and open lid then mix epoxy and hardener in a bowl. A leaking deck, especially with wood cores, can lead to core rot and eventually delamination of the deck and loss of structural rigidity. To make the plywood of the boat waterproof follow the below given steps: Clean the sides of the veneered marine boat with a clean cloth. There are thousands of ply/epoxy boats built that are completely encapsulated. Many of the boats in Ken’s shop are there because of poor maintenance, improper storage or other forms of neglect. How To Seal The Plywood. When plywood is exposed to water or extreme humidity conditions it can cause the glue to come undone, weakening the entire integrity and foundation of the wood. You can choose any suitable sealant. Most all boats have some sort of “core” in the decks. I took PAR's and Gonzos (and others) sealing advice almost a decade ago when I did an extensive restoration on a small cruiser. Plywood that has been stored indoors and is still as dry (12%) as when manufactured, does not need to 'breath'. So I rebuild boats and have replaced sections of flooring before but this one I chose to rip the entire floor out and remove all the foam (what a pain that was) anyway this weekend I am going to put in the new floor, marine plywood, and drill and pour the new foam. Here is a step-by-step guide on how to do this. Although Marine-Grade Plywood is strong, durable, and heavily-resistant to moisture, an additional coat of seal is typically needed to prevent moisture from the wood’s doors. Next step is to take a paintbrush and fill all the holes and joints with epoxy. An oil based enamel paint IS a better option (tougher, longer lasting, better UV resistance) than varnish for sealing … Unfortunately, plywood is made by gluing layers of wood together where it is later finished with a veneer. Plywood is a wood that is oftentimes used on docks and boats. Unsealed seams diminish the effectiveness of the cooling and heating systems of a home which can adversely affect utility costs. First, sand the plywood surface with 80 grit sandpaper. Wait for three hours and then apply a second coat. The answer to this question is yes, Marine-Grade Plywood should be treated. The many layers of Marine Grade Plywood are held together with waterproof adhesive, allowing the wood to withstand direct contact with water. Whether it’s balsa, plywood or some of the foam cores all can eventually absorb water from a leaking deck penetration. Ken is comfortable using epoxy for a plywood bottom becuase plywood is “dimensionally stable”. Both the above posts are accurate advice. Among them, the best is using a wooden sealant. You might wince at the cost of coating with epoxy since the coating will possibly exceed the cost of the plywood itself but it is the only way to protect it. However, there are several ways of waterproofing plywood for a boat. Ordinary plywood usually has 3 to 5 layers, while marine plywood has ten layers or more. Any reasonably handy boat owner can caulk their own boat, there is no magic involved. With that said when I am done with that I have to seal it. As has been mentioned, for the deck on a bass boat, simply painting the plywood with a good quality oil based enamel (and maintaining it) will last for decades . 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