Plywood Hollowed Walls

[webbaldo]

After studying a few builds, I really liked the idea aggie etc use , with the 'skeleton' plywood.
(sorry for borrowing your image)


Ive noticed it was done in 3/4 plywood.

Now if I was to do this with 1/2 plywood, then have 1/8 inner and outer ply skins, then 1mm Alu on the outside would this be strong enough? I would be bonding all 3 wood layers with epoxy

I would be using 1/2 polystyrene or celotex insulation in the centre.

Im just trying to keep weight down whereever I can really but I still want even a little insulation.

[Forrest747]

Yes taht will be stong enough. looking at 1000 lbs of support per wall. also go with gorilla wood glue and clamp you will be ok and cheaper than epoxy. Wish i had teh confidence i have now and i way overbuilt mine. oh well there is the next one.

I did some test a while back on the strength of plywood take it for what its worth.
http://www.tnttt.com/viewtopic.php?f=21&t=47534

[parnold]

Definately strong enough. I went with 3/4 thick walls for ease of insulating. Didn't need it for strength.

[grant whipp]

1/2" plywood for the core wall will be fine ... but if you will be gluing the aluminum to your side walls then I'd suggest 1/4" sheathing on the outside of the plywood core ... I've found that the expansion of the aluminum in direct sunlight is just enough to make 1/8" sheathing "pattern through". I've been gluing .040" aluminum to 1/4" sheathing for years with no problems.

Good Luck, and as always ...

CHEERS!

[webbaldo]

1/2" plywood for the core wall will be fine ... but if you will be gluing the aluminum to your side walls then I'd suggest 1/4" sheathing on the outside of the plywood core ... I've found that the expansion of the aluminum in direct sunlight is just enough to make 1/8" sheathing "pattern through". I've been gluing .040" aluminum to 1/4" sheathing for years with no problems.

Good Luck, and as always ...

CHEERS!

Thanks for the advice, when you say sheathing, do you mean 1/4 ply or something else? Excuse my ignorance!

Also my original plan to try and make the whole thing waterproof as possible was to cover everything in epoxy as well as using it for glue.

Instead, would using titebond glue, then polyurethane for waterproofing be a good (and cheaper) alternative? I want it well built but trying to keep costs down.

Or is there no cheap way to do it? Am I better using titebond to glue it all, then use Epoxy to seal the finished 'sandwich'?

My other worry is that I was gonna use contact adhesive or 3m 4200 to glue the aluminium on. If I epoxy the wood underneath, will the adhesive still work?

[bobhenry]

My little 4x7 was built with 7/16 OSB and after the build I lined it inside with 3/4 blue foam wrapped in a nice soft material. It gave the interior a nice finished look and allowed me to insulate completely. It is quite solid and I have no concernes about the strength of the unit.





http://www.tnttt.com/viewtopic.php?f=50&t=38489

[grant whipp]

Thanks for the advice, when you say sheathing, do you mean 1/4 ply or something else?

Yes, 1/4" ply ... some folks use luan, some birch, some just common fir plywood ... "sheathing" is just a general term for what ever covers the framework.

Also my original plan to try and make the whole thing waterproof as possible was to cover everything in epoxy as well as using it for glue.

Instead, would using titebond glue, then polyurethane for waterproofing be a good (and cheaper) alternative? I want it well built but trying to keep costs down.

Or is there no cheap way to do it? Am I better using titebond to glue it all, then use Epoxy to seal the finished 'sandwich'?

I'm not a good one to ask about that ... ... as I, personally, don't agree with completely encapsulating the wood in a trailer (completely sealing everything, whether it is varnish, polyurethane, epoxy, or what ever). My take is that wood's inherit nature is to absorb ambient moisture and then dispel it in its own good way ... when you completely seal the wood, you prevent this from happening, and if you ever compromise the seal (whether from a scratch or other slight damage), you give moisture a way to get in but not out, and thereby give way to the beginnings of wood rot. Waterproof the outside, but give the wood the ability to "breath" on the inside. Others' opinions will vary ... it's been a long-standing debate among the wooden boat crowd ... ...

My other worry is that I was gonna use contact adhesive or 3m 4200 to glue the aluminium on. If I epoxy the wood underneath, will the adhesive still work?

Yes, the adhesive will still work ... but make sure it is a "soft-setting" adhesive like Rubber Roof Cement, Vinyl Top Adhesive, or the like (common contact cement is a "hard-setting" glue, and will not allow the aluminum to expand & contract very much without either delaminating the cement bond or the glue holding the plywood together) ... and I always recommend "floating" the roof & hatch skins.

Continued Good Luck, and as always ...

CHEERS!

[webbaldo]

Grant, thanks for the extra advice. Good food for thought