Plywood shell/skin. Seal- spar urethane both sides or just one?

[drewspuppet]

So I’ve got a pretty large trailer build 19’x7.5’ and right now have a bunch of luan sandwiches to assemble and finish.

Due to cost I’m wanting to skin in 1/4” mdo plywood and seal/paint. It’s something that if doesn’t work out I can fix or change down the road.

2x2s, 1.5” foamular and super thin luan.

Would using the urethane on both sides of the 1/4” help prevent warp, etc? Needed?

Thank u for your info

 

[rruff]

I built a camper like this over 20 years back. I'd highly recommend epoxy-fiberglass as your exterior coat over the luan, then paint. You can do most of that before you assemble the panels if you wish.

 

[Teardropper]

Would using the urethane on both sides of the 1/4” help prevent warp

If I understand, you are asking if the inside of the sheathing should be varnished on the interior side before attaching to the framework.

I'll vote no.

I think sheathing should be attached using TB3 (and screws or crown staples), and any surface treatment will negate the glue's ability to grab the wood. I suggest TB3 instead of TB2 because it has double the open time to work with.

I sure didn't get any warping on my interior 1/8" BB sheathing:

Tony

P.S. I swear by Minwax oil-based polyurethane.

 

[Joe917]

Fiberglass and epoxy the exterior

 

[drewspuppet]

Tony, what kind of paint did you use over the oil based minwax ?

Tony

P.S. I swear by Minwax oil-based

 

[Teardropper]

Tony, what kind of paint did you use over the oil based minwax ?

I just use Minwaxy polyurethane on the interior and galley.

The exterior is fiberglass/epoxy with Monstanliner.

Tony

 

[jwiereng]

Fiberglass and epoxy the exterior

Would it be sufficiently waterproof with epoxy over plywood?

 

[Sparse Gray Hackle]

Would it be sufficiently waterproof with epoxy over plywood?

That depends on your skill with epoxy and glass. In the boating world, a sealing coat of epoxy is often used prior to laying the glass. Check out the Gougeon Brothers book on boat construction.

 

[Teardropper]

Would it be sufficiently waterproof with epoxy over plywood?

Well... maybe. But why risk it? Add a layer of 4 or 6 oz cloth. It's just about as easy as adding epoxy.


Tony