Finish for Marine Plywood

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jtf

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I have read many times here about the combo finish for plywood. I used a high grade marine plywood to deck the floor and don't think it requires the extra ingredients other than a good+ grade exterior paint. I can get an oil base or go with Rustoleum water base.

Also the plywood is A/B sides, both top bottom will get a double coat. Fortunately the Weldbilt has level floor ribs extra wide, no need for additional floor bracing.
 
Marine epoxy is a good way to encapsulate wood in a boat. It is not UV resistant and either needs paint or varnish .
 
Marine grade and exterior grade plywood's are not rot proof, they are made with waterproof glues. The main difference between marine plywood and exterior plywood is that the marine plywood is made from higher quality ply's with no voids.
I sealed my plywood transom and flooring with the Old times formula then painted with Rustoleum oil based.
 
You should definitely seal it, marine ply often is treated in a similar fashion to pressure treated with a high copper content. This can cause galvanic corrosion, so you definitely want to isolate the ply from the aluminum.
 
Ditto what Dale said about the sides of wood.

What I have had outstanding success with over the years, is Thompson's "Wood Preserver."

This product goes on clear and absorbs into the wood, and disappears. Apply 2 coats, and especially around the edges and in cuts. Once it's dry, you almost can't tell anything has been done, except for a slight darkening of the color.

Not sure what's in it, but it's stinky stuff, and it really works. Better than lacquer, urethane or epoxy, in my experience, as it's not sitting on top of the wood, but is actually inside the wood. So it can't crack or peel off and let water in.

We used to build sheds out of untreated pine T1-11 wood. Once all the cuts were made, we would use a garden sprayer to soak the siding with wood preserver. Those sheds lasted many years with no rot. Most people thought the natural wood was so pretty they didn't even paint them. We would recommend re-treating them every 2-3 years, as rain would splash mud on them, and leaves would build up around them and so on. But in all those years, never had a customer tell us the shed was rotting.

Since then, have used that product for anything, and it is simply outstanding. In boats, I have used it for the decking, and so far, none have gotten soft. The more years I use it, the more confident I am in it's effectiveness.

One cool thing about it that I really like, is that after it dries, you can use glues, adhesives, contact cement, and so on with no issues. Yet, spray water on it, and it beads off, like a waxed car. GREAT stuff!
 
Is anyone aware whether the Thompsons wood seal causes aluminum rot? (I'm thinking about pressure treated wood which is highly aggressive on aluminum, although obviously a different product from the Thompsons).
 
Wouldn't ignoring the side ply be like brushing only one side of your teeth? Thanks for the friendly "heads-up."

This mix should make a fine primer for Rustoleum oil marine top coat. Covers well, soaking as I write.

One of my woodworking friends of 40 years uses this on his handmade chairs and great wheels. And it is the same mix I've used for three years on my specialty boxes. Didn't know it was effective for wet conditions. However, one of my painters is skeptical. We'll test and see.

Smells good too. The decking sheet is about $80, just a bit more than the 3/4 gallon combo plus marine paint.
 

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