Plywood Question

[LDK]

I'm about to start working on the sidewalls and I'm using 3/4" oak plywood. My question is, I've noticed that the oak plywood is 11 ply thick where as 3/4" AC plywood is 7 ply thick. Could the oak plywood have possible deliminating issues later on? I plan on sealing all the edges but I can't help but wonder if I made the right decision on using the oak. Any comments.

[2bits]

I wonder what is AC ply? I am no expert in the area, but I would think that 11 ply thick sounds kinda funky. Again I am just throwing my thoughts out, but to me, more ply means more glue which means more possible failure issues, but please don't scrap your wood on my account! I hope some others chime in who know more about plywood. I just went to a good plywood "company" for the best quality, and because they are the only ones who have 4x10

[atahoekid]

In learning what I can from this forum and other sites, when it comes to plywood, the more layers the better. I don't know if there's some point of diminishing return.

In general I would also say that oka plywood is much better than AC plywood. Oak is hardwood, I'm not sure if AC ply is species specific or just some type of readily available softwood

I think you purchased the right stuff

[NathanL]

AC just refers to the faces, A face on one side and C face on the other.

Typically (but not always) the better the quality the plywood the more plys it will have for a given thickness.

But that doesn't determine if it's exterior, marine grade, or interior grade plwyood.

[bobhenry]

the "AC" is an appearance grade. You have an "A" face( the oak veneer )
and a "C" face which I would describe as decent with few fills.

CDX is common as home sheathing there is a c face(filled knots) , a d face (unfilled knots) and the x is exterior grade glue.

By reducing the ply thickness you take away the muscle that allows the wood to flex and seperate. The thinner the ply the less power it has to distort. Think of that horseshoe shaped 2x4 at the lumber yard and yet the yardstick that has sat in the corner for years is just fine. All good cabinet grade stock is wafer thin ply after ply none strong enough to cause ply seperation but combined they are very strong and stable. What you have is most likely interior grade so seal each and every cut edge.
Yes with help it can be used as exterior but you must protect the glue from serious moisture intrusion.

[LDK]

The AC plywood or ACX is what I used for the floor. It's in the kuffel creek manual. I'm building a solid wall construction and before I get to the point of no return I thought I would ask questions on the oak ply. I bought the oak ply at a local lumber yard. Also I had the oak plywood laying down on the garage floor on 2x4's and one of the boards has a slight warp. That and the 11 ply thickness got me panicking alittle bit.

[bobhenry]

Lesson ...Don't stack your plywood on warped 2x4's.....

What you need to remember is the floor holds the bottom edges square the spars if cut to match will true up the top. Your galley wall and a cabinet wall near the front will stiffen and true the sidewalls vertically so they can not belly out. There is a lot going on in that little box that will help that plywood to retain its shape. Getting it installed soon or storing correctly will keep your stock true untill the install.

[boomboomtulum]

In short, Plywood is graded on the face's quality. AA being the best with no face voids down to EE grades meant not to be seen, with many combo's of these ie: AB, AC, BC, CD etc. Than as mentioned the X's in there for exterior use or where moisture may be present, which is the same wood but using a moisture resistent glue which is to prevent delamanation of the plys. Water proof glues used in Marine ply are a whole other thing and can be $$$ spendy.

I used no exterior Ply on my build at all. Maple ply & Baltic Birch. 1/2 BB for the floor & 3/4 Maple for the sides all wood is sealed, treated, varnished epoxied etc. no exposed surfaces anywhere. Nice thing about BB is either very small or no voids at all between plys. I found a local vender who carried 4x10 sheets of the 3/4 maple and others in AB, of course the A is outside. The readliy available Oak ply from Box Stores will be a very thin Oak veneer with other woods between, could be hardwoods & soft in combinations, better ply will use the same species of wood throughout with the best on the outside faces. Of course you pay more for that. In general I will not but ply from the Big box stores except maybe for a Dog house or something, the quality is just not there.

You have found a better grade of Oak it sounds like with 11 plys, being exterior will not matter with a proper treatment on the edges it will last mant years. Remember water is the enemy.
Just my opinion or 2 c.

[Rock]

Your plywood warped because one face is down against the relatively damp concrete and one face is up against the dry air with good circulation.

Store your plywood on edge.

As others have mentioned - plywood varies widely in quality. Even the coding system allows for all sorts of wiggle room as you're seeing.

The # of plys have no relation to risk of delamination. My tear is made from 1/4" Sapele plywood which was almost certainly intended for interior wall paneling only. It's sealed 100% in epoxy. Pygmyboats.com used to sell a kayak made out of a marine grade of the same plywood. It's all in how you treat it.

Eric

[LDK]

I called the lumber yard this morning and the man said it was interior grade oak plywood. I told him what I was doing and he said I could seal it with polyurethane and it would be ok. Is there anything better than polyurethane that I could use and get locally?

[LDK]

Lesson ...Don't stack your plywood on warped 2x4's.....

What you need to remember is the floor holds the bottom edges square the spars if cut to match will true up the top. Your galley wall and a cabinet wall near the front will stiffen and true the sidewalls vertically so they can not belly out. There is a lot going on in that little box that will help that plywood to retain its shape. Getting it installed soon or storing correctly will keep your stock true untill the install.

I made sure the 2x4's were straight before I put the ply on it. The problem is my garage floor isn't very level and that was the culprit.
The plywood is just slightly warp. Only one board.

[mikeschn]

I built an Escape Hatch/Winter Warrior with Baltic Birch. I don't remember how many plys it was, but it was a lot. But in retrospect, it must have been interior glue, because in less than a year it was delaminating.

I sold it for parts...

I now have a phobia for plywood that is made with interior glue...

Mike...

[LDK]

I built an Escape Hatch/Winter Warrior with Baltic Birch. I don't remember how many plys it was, but it was a lot. But in retrospect, it must have been interior glue, because in less than a year it was delaminating.

I sold it for parts...

I now have a phobia for plywood that is made with interior glue...

Mike...

You're scaring me Mike!!

[2bits]

I am glad some people chimed in and corrected my theory on the ply's! I however totally disagree about storing your plywood on edge to prevent warping!

[Dusty82]

Same here - at the cabinet shop, we stored our plywood laying flat on pallets to keep it off the floor. Standing it up can create a bow, depending on how far out from the wall the bottom edge sits and the thickness of the plywood.

The finer grades of cabinet plywood, like oak, cherry, maple, and such are usually designed and made for interior applications. They're just not made to handle the weather and constant UV bombardment that a trailer body sees daily. The exception is Marine Grade, which is made for wetter, more humid applications, and contains water resistant glues. Marine grade plywood is NOT waterproof, but resists delamination better than cabinet grade plywood.

ACX is a great option for building TDs and TTTs, but there really isn't a totally waterproof plywood on the market. Unfortunately, you're kind of limited to fir and pine when it comes to ACX, but you can certainly use a high-temp contact cement to apply a veneer to the ACX.

This is all assuming that you don't encapsulate the plywood in epoxy or fiberglass over it. If you completely encapsulate the plywood, you'll have a very durable finish over the plywood that will resist weather and UV very well. As for fiberglass, they've been building Corvettes out of it since 1953, and boats for longer than that. I've never heard of any fiberglass problems in a Corvette, and when it comes to boats, you always get what you pay for.