Re: Treated plywood
In my part of the country, all of the old CCA and the newer ACQ is yellow pine which is a closed grain wood and when allowed to dry in the sun will tend to warp an buckle. I did stick frame houses for a while and anytime we would bust a bundle, I would make the guys strap it back as soon as they got what they needed out of the unit. Unit being a full bundle of plywood.
AC Exterior or even AD Exterior would be what I would use sealed (especially on the edges and inside any holes where the end grain of the filler plies are) using Spar. Spar was developed for marine use years ago and is a hybrid. End Grain is what will get you. It is a direct route for moisture to wick into the wood.
ACX/ADX should be SPF outer plies with a cheaper wood such as Luaun Mahogany (which isn't really Mahogany) for the filler cores. Spruce, Pine, and Fur (SPF) are all open grain woods and doesn't warp as bad, not to say that they won't.
About 20 years ago the plywood industry changed how they graded plywood and went to a more open standard allowing more voids in the filler plies and the construction grades are loaded with "soft spots" in CDX versions. The "A", "B", "C", "D" are grades with "A" being better than "B" and so on. This comes form the look and the amount of sanding. "A" will have very few "football" plugs, while "D" will be loaded with them. Lumber Core has a solid wood filler with either AA or AB finish, but uses an interior glue for laminating.
Actual Marine Plywood would be the preferred due to its greater number of plies and greater absence of voids in the filler plies and true Marine Plywood carries stamping to certify it, some even to Loyd's of London and British Standards and is tested to moisture and even boiling, but sealed correctly the ACX or ADX will last a long, long time.
I now work on aircraft parts and I see the damaged caused by corrosion almost every day and I wouldn't put ANYTHING against AL that would even slightly, hazard my boat.
