Seal ply skin before aluminum?

Finishes, paints and coatings

Seal ply skin before aluminum?

Postby SkookumAJ » Sun Feb 16, 2014 8:30 pm

Hello everybody!
Well for the first time in my build I've come to a place where I'm just not sure if I should do a step or not.. So I put it to the collective wisdom of Tnttt.
I'm ready to skin my cabin with aluminum, but I am wondering if I should seal my plywood underskin. The reason I'm considering this is because I live in British Columbia, Canada, and it rains A LOT. The humidity outside is currently 92%, and wood that is outside (even covered) swells with moisture of course and mildew/mold can get going pretty quick.. and we do not want that..
But, if I seal, will the Sikaflex (very flexible super-adhesive) not bond as well as to bare wood?
So do people do this, or am I thinking too much??

Thanks! AJ
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Re: Seal ply skin before aluminum?

Postby tony.latham » Sun Feb 16, 2014 11:23 pm

My first tear was commercially made and I had some moisture issues with it. On this build, I encapsulated it with epoxy prior to applying the aluminum. The sealant will stick, it's normally applied to paint.

Anybody else weigh in with this? What'd they do back in the 40's?

Tony
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Re: Seal ply skin before aluminum?

Postby jonw » Mon Feb 17, 2014 9:18 am

I'd recommend at least sealing all plywood edges, whether they are exposed or not. It wouldn't hurt do seal the exterior surfaces as well, but I don't know about the Sitkaflex.

You could just let the aluminum float at be attached only at the edges, held in place by the screws in your edge molding (for the roof pieces) - that's what I did and have had no problems...

Good luck!
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Re: Seal ply skin before aluminum?

Postby George Taylor » Mon Feb 17, 2014 5:59 pm

I coated our tear with 3 thick coats of Spar varnish then installed the aluminum skin. I did not care what the varnish looked like, since it would not be visible, so I just used a roller to apply it. The aluminum is attached with strips in the center that I drilled holes into for screws. Just a dab of sealant and installed the screws.
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Re: Seal ply skin before aluminum?

Postby SkookumAJ » Sat Mar 08, 2014 1:13 pm

Thanks Guys!
The sun came out for a day, so i dropped everything and rolled on some polyurathane.. easy enough...
And I'm now onto alum skinning!

Cheers! AJ
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Re: Seal ply skin before aluminum?

Postby cleburnescv1937 » Wed Mar 12, 2014 4:33 pm

Spar varnish been used for years for sealing boats.
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