plywood choices for floor and transom

[Kracker Jack]

Do you necessarly need to use a marine grade? I have heard some things you can do to a standard plywoods instead of using marine grade. Can I get some positives and negatives on all different applications. Thanks in advance

[Kracker Jack]

can i get some positives and negatives on different types of plywood and techniques for prepping non-treated

[Kracker Jack]

Hedge i read a thread on here on "hot coating" a b/c type ply. By rolling on non hardened resin let it sit over night then roll on a hardened resin then sand and apply. by hardened I mean mixed and non mixed. Im not trying to cut corners im just looking at about 15 sheets of 3/4 birch cabinet grade that was made and china and is far from finish grade that was given to me.

[baconaneggs]

As a builder, I have used some of the Chinese 3/4 birch. It is much less expensive than the the US version carried by my lumber yard. The first time I used it was on a study/office renovation. We built up numerous built in cabinets and proceded to prime them in place after installation. You can imagine my delight when the vaneer began to delaminate and wrinkle after application of a oil based primer. We have used latex primer on the good stuff and have never had any problems I think I saved about 400 on the job. I figured I lost about 3000. I would strongly recomend you buy a marine plywood to do any repairs. A house is only as good as it's foundation. Why skimp on your boat. And he is right, treated pw is very wet and takes forever to dry. when it does, it looks like a potato chip! Or a taco.

[Kracker Jack]

baconaneggs same here with this ply!!thin veneer!!! I just figured it would be a little different using a resin and hardener on it rather than your issue using a latex or "water base" paint. once again not trying to cut corners. There are alot of threads on here were guys are using 3/4 untreated plys in fully encapsulated situations such as transoms and floors. im just trying to get every ones opinions. Is marine ply treated? or is it just the quality of glues they use to laminate the plywood that makes it marine grade?

[jeffmo]

every time i have used plywood on one of my boats i used marine grade.after cutting the pieces to whatever size i needed i would apply a couple of coats of helmsman spar for added protection.

[baconaneggs]

KJ, upon giving it a little more thought, the whole idea of encapsulating the wood is to prevent it from absorbing water. So using a piece of treated pw that has been in a warehouse drying seems like a good idea. However it is pressure treated, so it does tend to squirm around during the treatment process as the different veneers absorb fluid at different rates and move in different directions, leading to a sheet that is not totally straight or dimensioned properly. Is it as strong as it once was? I don't know. Marine plywood conforms to a much higher standard than regular plywood. It has waterproof glues and decay resistant wood species. You have to know in the back of your mind that if you used marine pw, you would never have to worry about the quality of your work. But everytime you saw a thread about stringers or transoms, there would be a twinge of doubt! What ever you use, just pay attention to any cuts, limber holes, and chase ways. ultimately it is the penatrations through the encapsulating cover that leads to the downfall. I'm ripping apart a 73 center console right now to replace the floor and stringers. I can't wait to see whats underneath!

[RidgeRunner]

Regular pressure treated plywood is a NO-NO. It will be so wet you will never have proper adhesion. Most treated plywood is Southern Yellow Pine which is not the best plywood to use in the first place. Pressure Treated Marine Plywood that has been Kiln Dried After Treatment is dry and will work. Marine Plywood is FIR and has a better grade of interior plies.(Less Voids) It is available with or without the pressure treatment.
All of the plywood of BC grade or better has a finish too smooth for my liking. I like to rough them up before laminating with resin. I do not know if the glue is different from regular exterior grade plywood. Most all of the delamination issues come into play due to lack of proper glue in the manufacture of the plywood. There are numerous brands and species. I wouldn't use a cabinet grade plywood for core on a boat. I would make certain that whatever I used it had Exterior Grade Glue. Look for the X on the end of the grade. (CDX, BCX, etc.) If you don't want to invest in the Marine Grade Plywood, at least go with Exterior Grade Fir. Okume is very nice but expensive. Happy hunting..

[Kracker Jack]

I just built a storage box for our duck decoys on my buddys Chincoteague scow. And we used salt treated he had laying around and the hollows in the layers and the soft plyable wood makes me nervous to use in structual applications such as a trannsom. And also resins and wet treated wood is like mixing oil and water. This salt treated plywood he had had been in his garage for like 6 monthes and it was all we had so we made due. As for the v20 im not wanting to put junk wood in my transom, but i am looking for functional money saving material that will serve my purpose. Thank you for all the info so far guys.

[spareparts]

I've used what I've been told is forming grade plywood with good luck, its the stuff with the red paint around the edges. Its not marine ply, but it doesn't cost like marine ply. resin seems to stick good to it, I redid the compartments on my Mitchell a few years back, that boat has been thru three owners since then, been used like a government mule. the work I did on it is still holding up last time I saw it