Aluminum direct to wood framing.

[ScottM]

I'm in the planning stages right now for a larger trailer. The dimensions are still TDB but 14-16ft long by 7-8 feet wide. I'm going to stick frame it with 2x2 and I have some 2' thick foam panels that I found for free for insulation. I have a place locally that will sell aluminum that is 103" wide and they sell it by the linear foot. Its .040 thick. Can I adhere the aluminum panel direct to my framing (using sika flex 221 or similar)or do I have to "skin" the trailer first in plywood and then attach the aluminum panel. Looking to save as much weight as possible is what's making me want to go this route. Planning to use FRP for the interior walls. Attached is my rough layout in case anyone is interested in what I'm working on. Thanks for any insight!

[QueticoBill]

My opinion is find an adhesive that will adhere the skins to the framing and the foam. I don't think framing only will wear well. A solid skin - even 1/8" ply - would work.

[tony.latham]

Can I adhere the aluminum panel direct to my framing (using sika flex 221 or similar)or do I have to "skin" the trailer first in plywood and then attach the aluminum panel.

I'm with Bill. Skin with 1/8" ply using glue and mechanical fittings. That will tie your framing members together and support the aluminum with a hard surface in the event of a hailstorm.

Tony

[QueticoBill]

I should clarify that while I did suggest adding ply as Tony describes, I believe it is possible to rely on the skin adhered directly to foam approach.

[ScottM]

Bill and Tony, thanks for the feedback! It is much appreciated. Bill, is you recommendation to adhere to the foam to help improve the structural integrity (racking strength) and tie everything together. Or just more surface for the aluminum to attach to so it doesn't fly off. I wonder if I ditch the FRP inside and switch to a 1/4 ply interior if that would do the trick and give the proper strength.

Tony, I live in Virginia so hail damage isn't a huge concern. Any hail we do get its typically very small. I'm going to price out 1/4 ply for the inside of the trailer today and see of that is a good option. 1/8" plywood may be hard to come by for me. If I skin the inside with something stronger than FRP do you think it still necessary to skin the outside first before I do the aluminum?

The foam I am using for insultation is 2" thick 4x8 sheets that were left over from a construction project. They have a paper backing I plan to peel off prior to install. The framing will be a true 2" thick to accommodate the foam by 1.5" wide. Ill be using ripped down 2x3's

[tony.latham]

If I skin the inside with something stronger than FRP do you think it still necessary to skin the outside first before I do the aluminum?

I think it has to be skinned in and out with thin plywood. (With glue and fasteners.) That will tie everything together. You'll not gain that strength with FRP or the aluminum on the outside.

The plywood sheeting creates two big gusset plates--inside and out--and turns the wall into a torsion box. It won't rattle apart.

Tony

[ScottM]

Tony, thanks for the feedback. I know you aren't a fan of Luan in general but I'm guessing it would be ok as a substrate. Local lumber supplier has 1/8 and 1/4 for around $20 bucks a sheet.

[tony.latham]

Tony, thanks for the feedback. I know you aren't a fan of Luan in general but I'm guessing it would be ok as a substrate. Local lumber supplier has 1/8 and 1/4 for around $20 bucks a sheet.

I think it would be fine. For 1/4" ply, I buy subflooring. It's cheaper here than 1/4" AC and has no voids.

Tony

[QueticoBill]

The foam-aluminum lamination protects the aluminum from deformation and makes it useful structurally. Does the same with FRP. They act like the canvas on a foamy. The skin is less stiff than ply by itself but adhered to the foam it's just as strong.

[tony.latham]

but adhered to the foam it's just as strong.

What adhesive?

Tony

[QueticoBill]

I would research it a bit but would look at 3M 30NF. Use 3M's help line. People I know swear by it for foam to practically anything: props, parade floats, outdoor stages, etc.

[KCStudly]

I 2nd the notion that plywood between foam and aluminum would be preferred. The foam will expand and contract quite a bit more than anything else and will constantly be trying to not be fair with the spars/studs. The uniform layer of ply will not only add rigidity, but it will fair everything out nicely and mitigate lines telegraphing thru aluminum. Without the plywood, those same points of unfairness will constantly be trying to break the bond between the aluminum and whatever. The weight savings isn't worth the hassle, and despite what you think your tolerance for wavy lines on the outward appearance is now, when you get so many hours into the project and decide it doesn't look worth the effort you've put in, you might get discouraged.