but a few coatings of polyurethane should seal the bottom and edges and last for yrs. Sand your plywood surface, removing any rough spots. Dave fishtales2b, Apr 6, 2014. fishtales2b, Apr 6, 2014. Much like any other form of plywood, if you want to stain, paint, or (in this case) seal it, it’s crucial that you sand it down first. It is also known as Lignu in Scandinavia and MultiWoodPrime for new wood applications and is often abbreviated to CPES. You could use marine-grade sealer, but this will require more coats and must be reapplied every 3 to 4 years. I'm building a new tank/vivarium for my lizard and while it is not going to be as damp as something like a frog tank, I still want it to be 100% sealed so I never have to worry about it (even if the inhabitants change down the road to something that needs to have rain-showers several times a day). Moreover, the epoxy, applied in multiple coats, forms a fantastic seal. No doubt epoxy is better but consodering that the floor is not always under water I would think polyester would be fine. Marine plywood is a type of wood specifically formulated for use in moist or wet areas. Roll the sealer across the surface of the marine plywood. I can't explain this but there's a long list of boat related things I can't explain.. It is almost always necessary to coat the marine plywood in additional sealer to block all moisture from the pores of the wood. Smiths Clear Penetrating Epoxy Sealer ™ (CPES™) is a thin epoxy that will penetrate deeply into the surface of wood. How can I stop this stop this problem with fewer coats? I've heard of sealing marine ply with just fiberglass resin itself. Saturate the foam brush, and start spreading it on the top and side edges first, switching to the front face of the wood when you're done. Apply about five thin coats of epoxy sealer. Roll the paint onto a 2-by-2-foot area to ensure the sealer does not dry before you cover the area. Marine grade plywood is not to be confused with similar types of plywood like pressure-treated plywood. Allow the coat to dry for one to two hours. This will take one or two hours. It is almost always necessary to coat the marine plywood in additional sealer to block all moisture from the pores of the wood. One unique thing about this type of wood is that it can resist water and moisture on its own. 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. Print. But just as importantly it can decorate the plywood if the exterior is going to be seen. yellowbelly80. Marine plywood is a type of wood specifically formulated for use in moist or wet areas. I agree on not using treated wood. I sealed mine with paint on truck bed lining I bought at Oreillys. However, you can give plywood even better water-proofing by sealing it with Aquarium sealant. A good rule of thumb is to add as many coats of sealant as there are in the plywood. Since marine plywood is typically used underwater, you’ll need to treat every surface of the wood with sealant. Wash the paintbrush by pouring paint thinner over the bristles and then running the brush under warm running water to remove any residue. Drag the brush in a different direction each time. Drag a foam tipping brush over the sealer while it is still wet to remove brush marks from the epoxy sealer. Apr 6, 2014 #2 . Marine plywood is thicker than typical plywood, so you’ll need to apply more coats to maximize its lifespan. Gently scuff up the wood with sandpaper between each coat for maximum adhesion, and be sure to wipe off any dust before adding the next layer.