Foam/Plywood Sandwich Question

[mjewell5]

Hello all:

Last winter I built my Teardrop out of 3/4" ply, and used 1/8" Birch plywood for the roof and ceiling, as well as the inner and outer skins on the hatch.

The one thing that impressed me with the 1/8" ply is how stable it has proven to be on my camper. It bent easily enough, holds its shape extremely well, and looks awesome with paint on it.

I'm wondering if anyone has used this type of plywood or similar to build a foam sandwich structure, with 1/8" ply glued to both sides of the foam. In my head I can see building subassemblies in this way, and securing everything using tabs and slots to form a very strong, integral structure. Building in this manner would certainly result in a much lighter build, but have the strength to be used as an off road camper.

Thoughts anyone?

Mike

[ghcoe]

Not sure about the sandwich method, but I believe the foam canvas structure is plenty strong by itself for a off road trailer.

[tony.latham]

I built this little 4 x 8' for my sister.



The walls are skeletonized 1/2" AC plywood, sheathed with 1/8" Baltic on the interior and 1/4" underlayment on the outside. There's no doubt the 1/8" Baltic would have have done the job, I'd just have to plan on the alternate butt joints for and aft since it's only 5' long.



If I were to build that 'drop again, I'd probably bump up to 3/4" AC and get more aggressive on the skelontinzation to give it a deeper ceiling shelf (and end up with about the same internal weight). I also think that as long as one incorporates the hard pink or blue XPS foam in the walls that 1/8" Baltic would be fine for both sides of the wall. No doubt about it.

I really like the 4 x 8', 1/4" underlayment plywood though. Solid core, no footballs, doesn't mind getting wet and it's $22 a sheet here.

Tony

[yrock87]

I sandwiched 1/8 Baltic birch ply around 1 inch xps foam. I used minimal framing and have been very happy with how it has turned out so far. you can see in this photo where I cut out my roof vent and then stood on the 14 inch foam ply square. No lumber framing in this chunk,just foam and ply. I only have 3 roof spars total, one front, one back, and one at the roof vent. And I climb half onto my roof, putting my full weight on the roof edge during construction.

Time will tell how my tear holds up, but I am confident that the ply foam sandwich is a strongand lightweight technique that will last.

[Andrew Herrick]

Dagnamit, today I was just reading an 11-page thread on here about a guy - CaptainSam, maybe? - who's experimenting with homegrown foam core SIPS, which is basically what you're talking about - and I can't find the thread! It's a good read, though, should you find it.

I've done what you're talking about - many people have - and we love it. I've never gone so far as to make the "tabs and slots," though. You mean like a finger joint? Better cut carefully! You might be better off just using industrial-grade adhesives to join panels instead of finagling with a complicated joint.

Don't skimp on your glue. Some sort of polyurethane glue (with pressure applied during curing) has worked best for most people. I like double-stick tape.

One more quick thought on an off-road model ... Although the teardrop needs to be beefy to survive off-road conditions, of course, installing the right suspension will go MUCH FARTHER in reducing shocks and vibration. Sizing your springs to match your trailer load, for instance, will be far easier - and faster - than creating interlocking corner joints to handle the shocks from a undersprung suspension.

Good thinking!

[KCStudly]

Although the teardrop needs to be beefy to survive off-road conditions, of course, installing the right suspension will go MUCH FARTHER in reducing shocks and vibration. Sizing your springs to match your trailer load, for instance, will be far easier - and faster - than creating interlocking corner joints to handle the shocks from a undersprung suspension.

This. ^

Also applies to an over sprung suspension.