Aluminium skinning

[mike_c]

After reading this thread I'm concerned that I might not have done ours right, LOL. Anyway, I glued 0.040 mill finish aluminum to the plywood walls and the plywood galley hatch with contact cement, then "floated" them with screws and aluminum angle trim around all the edges, using Vulkem 116 caulk to seal it all up. On our recent trip across the southwest in summer, it was 107 F in Arizona and in direct sun the aluminum skin visibly delaminated from the underlying plywood-- it was too hot to touch, really-- but it cooled and flattened out nicely after sundown. Maybe that's the best of both worlds, although I did not use any high tech solution, just old school trim, screws, glue, and caulk. I can't think of any good reason NOT to glue it down first-- it certainly makes trimming and caulking easier-- but I would not rely on just glue since it's guaranteed to delaminate in hot sun eventually.

[markhusbands]

Well, that sounds like what happens to most folks that glue: it never really causes a problem, it just pops off when the aluminum expands. And you end up with a floating skin.

[ssrjim]

Well, that sounds like what happens to most folks that glue: it never really causes a problem, it just pops off when the aluminum expands. And you end up with a floating skin.

That is what happens here I get huge "bubbles" in the summer.

[taildragger]

That is what happens here I get huge "bubbles" in the summer.

So the answer is half clear- must be something and not obligingly aluminum, which "plays" (expands and shrinks) along plywood roof skin without bubbles. The second half of the answer is about this something

[citylights]

If you are getting expansion bubbles, then the aluminum is not completely floating... Not enough room for the expansion. Typical mistake is to use self tapping screws. Every screw hole is tight with no room for movement. Another one is to cut the aluminum to the exact size as the sidewall, then apply tight fitting edge trim, once again no room for movement.

Ideal would be to pre drill every screw hole through the aluminum (but not too deep into the underlaying wood) 1/8th bigger than the shaft of the screw to give room for movement. The screw head and angle trim hide the slop. Also to cut the aluminum sheets 1/4 inch smaller on all sides than the sidewall of the tear with 1-inch trim angle covering the gaps. Not very practical, but I may try the oversize drilled screw holes at least. Others have suggested not binding the bottom edge so that it can float better and absorb the movement, but I want mine sealed with angle trim on all sides.

Another trick that I have seen suggested is to apply the aluminum sun heated and already expanded. Then it will only shrink and be sure to have enough expansion room... Until you visit Death Valley in the summer. (By the way, I would NOT recommend visiting DV in the summer. That place is strictly winter and early spring only!)