Re-skinning the roof of The Coffin

[eggsalad]

In my original build, I skinned the (non-curved) roof of my TTT with 3/16" Masonite (hardboard) and covered it with 4mm Coroplast.

Despite what other people have built, the Coroplast did not last 9 months in the Las Vegas sun and UV.

I was fairly uncertain about the durability, so I trimmed out the roof in a way that would make it easy to re-skin

The time has come. Since I have a fairly rigid sub-roof, I really only need to "wallpaper" it for sun and (rare) rain protection.

I've seen 4' wide aluminum as thin as .019". I have played with some .032, but I think that's overkill in this application.

Two questions:

a] how thin can I go with this aluminum skin?
b] should I float the skin or glue it? If glue, what's a good adhesive to bond aluminum to Masonite?

Thanks,

eggsalad

[pchast]

I vote float it.

You have different materials that expand differently.

[eggsalad]

I vote float it.

You have different materials that expand differently.

Please help me understand how to accomplish floating. The roof is 48", but I've used 2x2" drip edge for the corner molding. Should I cut the skin to 47" or 46" and only screw down the vertical edge on the trim molding? That would allow for some expansion, but I would have to put silicone under the molding to actually seal it. Wouldn't that prevent expansion?

There will also be a 14" vent in the center. I think the flange would screw through the skin. that would prevent expansion, wouldn't it?

I'm kind of lost. Please help!

[pchast]

Me and my urge to comment...

Sorry, I have never done it. I've just read others.

There are several that have talked about it. I recommend that you
search the forum and send some private direct mail to them.

[48Rob]

Egg,

In general, the term "floating" when applied to a metal trailer roof means to only attach it at the edges (and around vents or protrusions) as opposed to the way the sides might be attached; with regular rows of screws/rivets/fasteners.

The roof sheeting should extend to the edges, and the trim placed over it.
The idea behind floating the roof is that it is generally a large piece of metal that is directly exposed to the hot sun, and thus will expand/contract more than other parts of the trailer.
If you try to attach with glue, or lots of fasteners, it will tug on them and can loosen.
Some people are afraid to use fasteners because "it might leak" though properly installed, on a well designed framework, a metal roof won't leak no matter how many fasteners are used.
Some of the concern comes from very poorly designed travel trailers of the 70's that would twist and rack, loosening fasteners that held them together.
Another more "teardrop" related issue is that people want to glue the metal roof to a sub layer of plywood, Masonite, or other sheeting.
The issue then becomes the metal sheet expands/contracts at a different rate than the sub sheeting causing the sheet of metal to bubble/blister-look really bad, and sometimes break the glue bond.
Usually the metal when cooled off will relax and lay flat again, but better to avoid the issue by floating the metal.
Rob

[citylights]

What Rob said!

When you float aluminum, the edge trim holds it on. Screw the edge trim through the skin. Use a flexible sealant between the trim and skin like butyl tape.

This is a detail area from the trim in my teardrop. If you look close, you can see the butyl tape squishing out from between the aluminum from when I screwed and squeezed it together.

[tony.latham]

I'd be concerned what a hail storm would do to .019 aluminum.

Here's what caught my attention in your thread: "I've used 2x2" drip edge for the corner molding" I assume that's galvanized steel? If you sheath your trailer in aluminum, I'd think that you'd end up with a nasty reaction between the galvanized surface and the aluminum, even after sealing. Other's might weigh in here but I think it'd be best to use aluminum trim (or angle) on aluminum sheathing.

And float it!

Tony

[eggsalad]

Okay, folks - now I understand the meaning of "floating". Thank you all!

I wasn't planning to glue down the skin anyhow, so I think it will be fine.

As for hail damage on a thin skin - I've never seen hail hereabouts, so that isn't an issue. Maybe highway gravel will ding it, but I'm not going to lose sleep over that.

As for galvanic corrosion between the aluminum and steel trim... the trim has a baked/painted finish, so that will slow it down, as well as the bead of silicone that will go between.

Also, this isn't intended to be a 100-year camper. Frankly, 10 years will make me happy!

[citylights]

Okay, folks - now I understand the meaning of "floating". Thank you all!

I wasn't planning to glue down the skin anyhow, so I think it will be fine.

As for hail damage on a thin skin - I've never seen hail hereabouts, so that isn't an issue. Maybe highway gravel will ding it, but I'm not going to lose sleep over that.

As for galvanic corrosion between the aluminum and steel trim... the trim has a baked/painted finish, so that will slow it down, as well as the bead of silicone that will go between.

Also, this isn't intended to be a 100-year camper. Frankly, 10 years will make me happy!

I have seen pea size hail in Las Vegas several times. Also hail in the mountains around.