Need quick answers on gluing Baltic Birch to foam.

[tony.latham]

I build acoustic guitars also and changes in humidity does change the shape of the wood so I get the concept.

I'm not a foamie guy so take this with a grain (block?) of salt --I'm speculating.

Since this is plywood... it shouldn't move as much as a guitar's soundboard. Plywood moves about 1/10th of what solid wood does.

But QB does have a point. It will move.

Me? I'm curious as to how you'll bond the plywood to the foam?

It's good to see your brain churning away.

Tony

[printer]

It never stops churning, the problem is deciding on which way to go. Yes, the plywood will move less than solid wood. Plywood guitars are better for camping than solid wood guitars. The plywood to foam should go on with Titebond from what I understand. I want to do a poor man's vacuum table using the floor of the trailer and wrap it in poly, then suck the air out using a shop vac. Only a a pound or two inches water column of pressure but over the whole area better than just throwing on a few weights. Might do that yet, did that with my original walls.

[tony.latham]

The plywood to foam should go on with Titebond from what I understand.

Gotcha.

Tony

[QueticoBill]

Well, just glue canvas to inside and then ply over the canvas.

The problem is the skin on one side expanding or CV contracting more or less than the skin on the other side. Good p-lam kitchen counters have a backer sheet - basic same stuf as p-lam with no decoration - on the bottom. I know of theatre gear - platforms and band shells - which have warped or twisted when exposed to humidity or water. Working from memory, ply might expand an 1/8" across 4' width with maximum humidity change. Combined with fabric shrinking with humidity as the fibers swell and tighten the weave, you could get bending ( I think, like natural fiber rope.)

I won't promise you'd be bothered by it. I cant calculate the bend. Just something that resulted in a very bad experience for me. I like both sides to have the same properties.