My Plywood sides are 3/4" and I was wondering do I need to seal the plywood if I am coving it with aluminum? I picked up a gallon of polyurethane sealer but if I don't need to seal the sides or the roof I would prefer not too. Any suggestions?
Hi Burro,
If you cover the plywood with aluminum, will the bottom of the walls (the edge that faces the road) also be covered, or will they be exposed?
As long as the plywood is 100% protected by the aluminum, then no, you don't need to.
Where you attach the aluminum and or edge trims and other parts, injecting sealer into the screw holes is advised as putty can shrink and sometimes screws can loosen and allow water in.
Almost always, when plywood gets wet and fails, the water is drawn in through the edges, so it is inexpensive insurance to up the odds by sealing them.
The polyurethane, if covered by the aluminum should work well.
Thinning it a bit for the first and or second coat helps it penetrate deeper.
You may need 4+ coats. Lightly sand or scuff after each coat, when it becomes very smooth and shiny and looks like it has formed a solid surface water can't get in, give it one more coat.
It doesn't take long to do just the edges, though you should wait a day between coats.
Rob