Question on waterproofing floating aluminum roof

Finishes, paints and coatings

Question on waterproofing floating aluminum roof

Postby daneyuleb » Sat Jan 27, 2018 2:25 pm

I'm floating an aluminum sheet on my flat topped, 8x5 painted plywood roof.

I've perused these forums but I"m still confused on just how to handle the edge sealing and really don't want to make a mistake.

I'm thinking I'll put 4 inch wide eternabond tape around all roof corners extending an inch down (along the walls which are plywood) and 3 inches on the roof.
Then lay down the aluminum sheet so it rests on top of the tape. It will be about 1/4 inch from the edge of the roof on all sides.
Then 1-inch "L" aluminum trim along the edges.
Stainless steel screws through the trim, tape and into the wood, but NOT into the aluminum sheet (so it will float freely).

My questions--

Would it be better to get 2 inch eternabond instead and put it OVER the aluminum instead of under? (2 inches would be needed in that case so the 1 inch trim can then cover it.)

And--in either scenario, I'm assuming caulk (with polyurethane) is still going to be needed--but where should that go? Between the trim and tape? Or between the tape and aluminum? And how permanent is it considering the expansion/contraction of the aluminum float? Won't it break down as the aluminum flexes?
daneyuleb
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Re: Question on waterproofing floating aluminum roof

Postby tony.latham » Sat Jan 27, 2018 11:11 pm

And--in either scenario, I'm assuming caulk (with polyurethane) is still going to be needed--but where should that go?


After the aluminum sheathing is fitted, dry fit the trim. You can gently persuade it with a dead-blow hammer. When you're satisfied, remove it and push some polyurethane sealant into the screw holes. Then lay a bead of sealant along the seam and reattach the trim.

Make sure you have whatever solvent the sealant suggests for cleanup along with a roll of paper towels.

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:thumbsup:

Tony :beer:

p.s. Dunno about the tape you're using but this method of sealing the seams works.
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Re: Question on waterproofing floating aluminum roof

Postby daneyuleb » Sun Jan 28, 2018 8:05 am

Thanks! Good advice on dry fitting it first. The trim fit should be easy since it's a flat top. My worry was about the sealant breaking down over time (especially with the aluminum expanding) and the tape is something I've seen people mention as better than something like butyl tape that wouldn't break down, but now I'm thinking I'll skip it and just use polyurethane sealant under the trip and that's it. Thanks so much for responding!
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Re: Question on waterproofing floating aluminum roof

Postby tony.latham » Sun Jan 28, 2018 11:55 am

My worry was about the sealant breaking down over time (especially with the aluminum expanding)


The sealant has more mobility potential than the aluminum can give it. :thumbsup:

Tony
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