Re-enforcing water damaged plywood?

agesilaus wrote:

valhalla360 wrote:
The problem with any of the penetrating epoxy solutions is by the time you open it up and get access to apply the epoxy...it's less effort to just cut out the bad plywood and put new in.

That's generally true, plus a sheet of plywood is a lot cheaper than those epoxys are.

This is true and really depends on how bad the water damage is. Epoxy resin by itself has little strength. If the plywood is intact a cheaper solution to these expensive low viscosity epoxies is to buy basic resin either epoxy or polyester and thin with a solvent like acetone. The viscosity will be like water and absorb into the plywood easier. Once absorbed the solvent will flash off very quickly. 40 years ago or so we used to buy a product to seal leaking molds called "Waterglass", using thinned resin with acetone was much cheaper and did the same thing. Also if the area is still moist or wet and you soak the area with acetone it will absorb that moisture and evaporate very quickly removing that moisture with it. Good luck if you decide to do this repair.

valhalla360 wrote:
The problem with any of the penetrating epoxy solutions is by the time you open it up and get access to apply the epoxy...it's less effort to just cut out the bad plywood and put new in.

That's generally true, plus a sheet of plywood is a lot cheaper than those epoxys are.

valhalla360 wrote:
The problem with any of the penetrating epoxy solutions is by the time you open it up and get access to apply the epoxy...it's less effort to just cut out the bad plywood and put new in.

Exactly. They (and most any other product) won't penetrate through plywood very well at all from the flat side, and none at all through vinyl wallpaper. You'd have to get it in amongst the plies, which basically means taking the wall apart, and at that point why not rebuild it properly?

Often when plywood gets wet, it looks to me like glue that binds the layers together gives out before the wood itself is extensively water damaged. That does depend a lot on the type of plywood used; marine plywood, in particular, has waterproof or at least very water resistant glue and so doesn't tend to break down in this way. That said, RV makers certainly don't use marine plywood on interior walls!

The problem with any of the penetrating epoxy solutions is by the time you open it up and get access to apply the epoxy...it's less effort to just cut out the bad plywood and put new in.

Look at CPES from www.rotdoctor.com
This is a very thin 2 part epoxy that will be absorbed by the wood. Once cured the wood will not be able to absorb any more water.

Although epoxies and repair products may work.....or may not....its certainly dependent on the extent of the water damage / rot and how much of the original wood is left intact to accept the product. Probably not much if any on an RV roof which is usually no more than 3/8 3 ply, and often thinner such as 8mm or 1/4". Might even be OSB.

Usually products like those mentioned are no more than band aids.

End grain plywood has an affinity for moisture.

Drying it out is imperative, before trying anything.

Let it drink some denatured alcohol, which will absorb the moisture when it evaporates. Lather rinse repeat.

Penetrating epoxies are very thin, and will wick deeply into end grain plywood.

Whether it is deep enough to reinforce that which you suspect is no longer as robust as it was before it got soaked, is another matter.

I really like System 3 clear coat resin for its ability to penetrate wood deeply. it is a very slow epoxy and has a lot of time to creep deep into the wood grain

SYS3 has other specific wood rot fix products too, which I have no experience with.

Heating the wood before adding the epoxy, will allow it to draw more epoxy in deeper when it cools and contracts.

Do not try to seal any wood that is not thoroughly dried out, and anything which dries fast is going to be creating its own heat, which will purge the moisture right through the epoxy/ or other resin and likely leave a path for moisture to try and get in again.

That heat and the denatured alcohol can allow one to mix and apply epoxy much sooner, than if they were just to wait for it to dry out on its own.

Check out " Abatron Liquid Wood " Very ssslllooowwww setting liquid epoxy that soaks in while curing. Actually approved for structural repair. Just follow directions to the letter even if it seems strange, something like mix for at least 1 minute and then let stand for 10 before using. believe me it needs the 10 mins.

Art.

Moved to Tech Issues forum from DIY.

Check out the West System (well known in the marine product world), they may have something. This is just general knowledge on my part and I haven't done what you want to do.