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hiphi45 12-23-2011 02:43 PM

Painting exterior plywood wall sheathing
Addition is concrete block for first floor and 2 x 6 framing with plywood sheathing for second floor. Both stories will be brick faced. Now I understand the concept of a drainage plane: that is if any moisture penetrates the brick (which it will) it will run down the space between the brick facia and either the bock or the tyvek wrapped plywood and out the weep holes the bottom of the brick wall.

The question is: Should both the plywood and the concrete block exterior surfaces be waterproofed before the tyvek is applied. I know that the theory is that tyvek acts like gortex in that it keeps the water out but allows the house to breath. Will painting the plywood put a moisture barrier in the wrong place thus trap moisture (escaping from the home's conditioned space in the winter) in the wall causing possible mold?

Bottom line: Water proof exterior (above grade portion) of block wall?
Water proof exterior plywood wall?
Just tyvek both the bare block (above grade)

Thanks much

titanoman 12-23-2011 03:48 PM

I don't think anybody here is going to tell you to paint it. And it is plywood, not osb (osb has a sealed side already)?

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hiphi45 12-24-2011 12:12 PM

I did not think so
But the concept of a drainage plane behind the brick facia wall seems so fundamental. Plywood is very prone to absorbing moisture. Keeping the moisture out of the plywood by sealing it on its exterior side makes sense to me. I understand why vapor barriers are almost always put on the warm (condition space) side of the wall. Will the latex paint of the outide of the plywood wall sheathing do any harm. The only possible harm that I can see is that it could possily trap moisture leaving the house. Tyvek is supposed to let moisture escape but block both moisture and cold air from pentrating the wall.

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