Polyester resin and plywood

[Whale1]

Just a question what types of ply can you use poly on?
Marine grade Ply , Construction ply untreated ?

I once glassed some bracing for a mold with treated ply and it lifted off by itself.
Please help

[alan white]

You can use polyester resin on either marine or untreated and it will adhere the same. The bond will last a while, but it will let go eventually, especially if water gets behind it.
The difference between marine and treated plywoods has to do with several major factors. The marine ply has fewer voids in the inner plies, it is made of a species of wood that can survive better in water, and it uses waterproof glue. That isn't to say non-marine plywood doesn't often share some of these attributes. It is just that the non-marine ply wasn't manufactured with all of those attributes in mind. If it can be used for boat construction, it wasn't because the manufacturer intended it to be.

Alan

[Trevlyns]

Hi Whale1 and welcome to the forum!

There has been so much discussed on this topic, I’d recommend you start reading up on some “similar threads”. Just scroll down to the bottom of this page. That will get you started!

Best

[Whale1]

thanks guys for the help.
So definatly dont use treated ply??

[PAR]

Treated plywood needs to be dry, which as found in most lumber stores, is still quite wet from the treatment process. The moisture content should be below 15%.

Polyester isn't the best choice for adhering a sheathing (in fact about the worst of the modern resins) vinylester is the best of the polys, with epoxy far better then any. It's a moisture vapor thing and good epoxy will keep over 99% of it out of the wood, where unrefined polyester (the cheap stuff) is lucky to keep out 90%. The moisture eventually permits the wood to swell and contract with content changes (a natural thing with wood). This movement eventually "sheers" the sheathing from the wood.

If you're going to use pressure treated plywood, check its moisture content before applying resin. This is true of any wood or wood product (like plywood).