Total plywood replacement?

[Steve L.]

All valid points but I'm more from the trying to keep it out school rather than the giving it a path out school. I'd resin the top, bottom and edges.

[brady hansen]

I think paint would add a layer of protection-but would eventually get blasted off. Resin, glass, or undercout could probably withstand the road damage much longer.

[Bigfoot Mike]

I have a houseboat and as you can imagine moisture and plywood rot is always on my mind. The boat I bought had already lost some plywood.

What I have found is that the new plywood itself needs to be protected from rot first - primer. Then a coating put over it. Fiberglass over plywood by itself has a tendency to allow moisture to get between the glass and the wood, then rot. A product called CPES is the best I've found. (one of those an ounce of prevention things.)

What is CPES Primer?
Clear Penetrating Epoxy Sealer (CPES) consists of a tough, flexible resin system in a solvent blend which aids in the restoration of rotted or deteriorated wood and the protection of new wood. The Epoxy Resin system chemically adheres to the wood fibers and significantly strengthens them while allowing for normal expansion and contraction.CPES is effective because of the special blend of solvents that allow it to migrate into the wood fibers and into the cellulose of the wood. Impregnation of the wood with the Clear Penetrating Epoxy Sealer changes the cellulose of the wood (which the bacteria and fungi find easily digestible) into epoxy impregnated cellulose which resists the fungi, while reinforcing the wood, and accomplishing restoration.

CPES is a two-part product. Mixes 1:1 equal parts of A and B by volume. Apply with brush, roller or immersion. Will cure down to 50 F. Also called MultiWoodPrime, CPES makes an excellent paint and varnish primer as it chemically bonds the finish deep inside the wood grain.

More info...
http://www.epoxywoodrestoration.ca/price7_050.htm

Here are some tests showing the benefits:
http://www.rotdoctor.com/test/polytest/polytest.html

One place to buy
http://www.star-distributing.com/smith/cpeswhy.html


I hope this helps.

[steven jones]

that rubberized roofing tar repair stuff might work good... you can brush it on...
--- steven

edit- on second thought, that CPES stuff looks much better...

[Bigfoot Mike]

I just found this study. (Y'all got me wondering). On soft wood like plywood, CPES works great. On Oak it seams everything has problems. Anyway, this is a good read on how well finishes hold up on new wood exposed to UV after finishing. I know ours is not exposed to UV, but hey, what the heck. It is really testing this stuff.

http://www.mar-k.com/wood_finish_testing_ii.html

[Pete Dumbleton]

If I felt I needed more protection on the bottom, I would just spray on automotive undercoat.

BTW, it makes a lot of sense to me that MDF and OSB would soak up more resin than plywood does because there's a lot more end grain in the first two and that's where wood really sucks up liquids.

[Frederick L. Simson]

If I felt I needed more protection on the bottom, I would just spray on automotive undercoat.

That's what I did with my '71 Compact Jr.

[Rob S.]

Hey All,

Coming into this discussion late. As mentioned before, do not use MDF. It is so much heavier (96lbs. 3/4"-4x8) and does not have the structural integrety needed. What I would use with an exposed undeside is MDO Ply (71lbs. 3/4"-4x8). This is the same exterior grade plywood that is used in the signage industry and what most of the blue highway signs for shops, resorts and camping area type signs are made with. Is is long term exterior grade and faced on both sides with a thin resin paper overlay. Takes paint really well as well as adhesive vinyl. Rather than a heavy undercoating you might consider buying a role of 3M vinyl and adhearing it to the ply and then installing it. This would give you a watertight underside without the weight and the vinyl comes with a 3-7 year warrenty and that is expossed to full sun and elements which the underside won't be.

http://www.boulterplywood.com/Exteri...ePlywood_4.htm

Rob