Newbie - Sealing Plywood Question

[stoveman]

I am using the Generic Benroy Plans as a basic plan to build by.I used 3/4" cabinet grade plywood from HD for the sides and the same for the floor.I applied an asphalt roofing sealer to the bottom of the floor and the bottom of the sides and glued and screwed the sides to the floor.That is where I am now.I read something here about sealing the plywood before finishing with 75% thinner and 25% polyurethane. Is this a good idea? Have I screwed up already with the sealer I used or the plywood I used?

I appreciate all the tips I've got already form this site and the people that took the time to post them.

Bob

[madjack]

...first off, if you sealed the bottom with asphalt emulsion, you should be good to go...personally, I would not recommend a more than 10-15% thinning of any poly...and then, use at least 4-6 coats of the stuff...when you thin something like poly, use it, the "thinner" will cause "holes" in the finish...hence the need for multiple coats...if you use poly, use it at near or full strength!!!!!!!!!
madjack

[TomW]

I have been searching for the answer to the same type of question about "sealing" the plywood.

I have been searching/reading about "Rot Doctor" CPES coating to seal the plywood. Do I still have to put a "primer" down over the CPES seal before applying the final color finish?

I have been looking at marine type paints for both the primer and top coats. If the marine primer is a two part primer, do I still need to put the CPES down first?

I have been trying to contact the paint maker about the marine paint I have been looking at but no answers yet.

Sorry, did not mean to hi-jack the original question.

[stoveman]

Thanks madjack. I was kind of worried that the cabinet grade plywood I bought was a mistake and I thought that a coat of thinned down poly would sink into the wood better to seal it before I put it on full strength. But if it doesn't make any difference I won't thin it.

Bob

[GPW]

Stove , we used a thinned poly , 75% MinSpt /25% poly and slobbered it on every part of out TD... soaked in very well and provides a good sealer ...we've used that trick in the past to waterproof cardboard for model planes... works ,and is cheap ... two coats is better than one ...
Primer over that and then paint ...

[madjack]

...well there ya go Stove, two diferent uses/experiences with the same product...go figure ...we do thin poly about 10-15% for spraying purposes...multiple coats is the trick here to get complete sealage and yes, we use 13ply 3/4" for walls and 11ply 1/2' for floors...it is a baltic birch cabinet grade ply with a poplar core...very stable...we get it thru a cabinet shop supplier, not the cheap chi-ply stuff from the box stores....
madjack

[stoveman]

Thanks Guys, I ended up splitting the difference and mixed it about 50/50 for the first coat and will put on 5 more coats not thinned.

Bob

[schaney]

Tomw - MultiWoodPrime / CPES is a sealer / primer and will chemically bond with many oil based finishes. The trick is to start applying your topcoat, I like Epifanes marine spars, in about 12 hours before your last coat of CPES has fully cured. If you send Smith Company the MSDS for the topcoat you want to use, they'll tell you if it will chemically bond. I've let CPES cure for a week or so and sucessfully topcoated it with Durabak and Target Coatings HybriVar with no primer.

For sealing and topcoating with the same product, I've recently started using Target Coatings HybriVar and really like it. It's a oil-modified, water cleanup finish. It soaks in much better than other polys I've used without thinning. It also levels out very nicely when brushed on. I'm very interested to see it's longevity in exterior usage being water-type.