Full size trailer side walls

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Full size trailer side walls

Postby theoldwizard1 » Wed Oct 02, 2019 12:43 pm

Many (most ?) new travel trailers are now using aluminum square/rectangular tubing the structure in walls. Some type of rigid foam is placed in the cavities. Internal and external sheathing is typically luan plywood (inexpensive and lightweight) or some type of non-organic panel (Azdel). The outer "skin" is typically a continuous roll of another non-organic (Filon).

I know in traditional "stick framed" residences, the sheathing is used to prevent the wall from racking along the face of the wall. It also provides a surface for attaching the finished exterior "skin" (vinyl, cementitious, etc siding) . Before plywood was cheap and plentiful, 1x6 material was diagonally "let in" to the 2x4s at the corners to prevent this racking.
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The rigid foam insulation used in a TT is obviously not sufficient to prevent the wall from racking.

If other means were used to prevent the walls from racking, could the rolled non-organic material (Filon) be applied directly to the studs and rigid foam or woul the "print though" ?
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Re: Full size trailer side walls

Postby tony.latham » Wed Oct 02, 2019 12:56 pm

Many (most ?) new travel trailers are now using...


The RV industry sets a bar just below your knees. They are built to make it through the three-year warranty. So don't try to follow their lead.

I would suggest you sub-sheath by gluing and screwing (or pneumatic crown staples) 1/4" exterior (or subfloor) plywood or 1/8" Baltic birch.

No "racking".

I have not used Filon so I can't answer your print-through question but I do know it's stiff.

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Re: Full size trailer side walls

Postby Pmullen503 » Wed Oct 02, 2019 3:36 pm

Be careful your subfloor or underlayment ply uses truly waterproof glue. I used IntegraPly which is recommended under tile. I thought it would be water resistant but it delaminated badly under PMF. Fortunately I only used it around my doors over foam but it was a chore to remove. Only the plys glued with TB2 were still stuck to the canvas and foam, the rest peeled right out. I replaced it with baltic birch, not marine grade but the piece I threw in a bucket of water did not delaminate after a week of soaking.
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Re: Full size trailer side walls

Postby Squigie » Wed Oct 02, 2019 5:42 pm

theoldwizard1 wrote:(...)
If other means were used to prevent the walls from racking, could the rolled non-organic material (Filon) be applied directly to the studs and rigid foam or woul the "print though" ?

If you get the frame materials perfectly flush, it would look fine.
But if there's any variation in thickness, time and heat cycles may eventually lead to what the steel boat world calls the "skinny cow" look.

All 'Filon'-skinned (and several aluminum-skinned) RVs or trailers that I've dug into far enough to see a wall cross section or full construction details have had something between the skin and the structure.
A few samples that come to mind:
For a time, Winnebago was using ~0.020" sheet steel between the steel frame (and foam core) and the fiberglass skin. The steel sheets were bonded with a good adhesive - no fasteners, whatsoever. Some 'waves' could be seen on the outside, but the overall appearance was pretty good.
Pretty much everything else that I've been into has had a laminated sheet of peeled and dehydrated tree carcass (a.k.a.: plywood).
...With one exception: I dismantled an '86 Winnebago that, in most areas, had a single wood ply - basically a ~3/64" veneer - between the continuous sheet fiberglass skin and the frame. The walls seemed to have been assembled while horizontal, from the outside in - skin, 'veneer', frame and foam, then wired and packed/padded where necessary, before treatments were added for the interior (various types of bracing, sheeting, etc. are used for wall/cabinet attachment points, table mounting, dent/puncture resistance around dinettes, heat protection, appliance mounting, etc.); and finally the interior skin (generally glued to the frame only).

The racking strength in all of the above came from the frame. The skins were doing much, if anything.

Personally, I wouldn't count on adhesive between dissimilar materials for racking strength. Sheet, glue, and screw!
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Re: Full size trailer side walls

Postby bobhenry » Fri Oct 04, 2019 4:31 am

What is wrong with downsizing the let in wind bracing it worked in the roof trusses and side walls of the barn camper..........

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they were incorporated on all four corners in the walls and the roof with excellent results for 6 years and several thousand miles.
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