3/4″ gap between drywall and block ext..
Chaddy123
| Posted in Energy, Heating & Insulation on
I’ve got a 3/4″ gap between the backside of my drywall and the cement block exterior walls of my house (1951 Cape Cod style). They attached 1×3 vertical strips to the interior block face, then hung the drywall from these strips (one can drop a marble from the attic to the basement via this gap).
I know better than to just seal off this gap, for fear of moisture permeating the drywall and condensing when it hits the cold interior face of the block.
Do I try to fill the 3/4″ cavities with a low-expansion pourable foam, or do I just vent it to the indoor airspace? I shudder to think what the interior surface temperature of the block is in winter (SE PA).
Opinions? Thanks in advance!
Replies
I have a house like yours. During a bathroom remodel, I inserted white styrofome panels between the firring strips before I replaced the cement board/sheetrock.
I never heard of pourable foam?
Heh, I was hoping to NOT remove the drywall, but I'm glad you took advantage of it during the remodel.
Pourable foam is available from a variety of vendors - it is often used in the marine industry for filling boat hulls, float barrels for docks, etc. It is basically like spray foam, but takes time to set up, so you can mix the two parts and then pour into place before it begins to foam.
That stuff has a pretty high expansion factor as it sets, i would be real worried about it pushing out the sheet rock.
Let's not confuse the issue with facts!
I'm thinking that you might get some separation issues if you use an expanding foam. Unless they're solidly anchored, the furring might pull away from the blocks. And, unless the drywall is well attached, it may separate from the furring. (Nobody knew about drywall screws in 1951. - lol)
I would suggest that if this was a problem, you have had the best part of 60 years to see it. Do you see any moisture problems?
My guess is that 60 years of painting has done a pretty good job of moisture blocking the walls.
Point taken...
I can say that it has not been a problem historically because the gap is vented to the attic space, which is poorly insulated. My concern is what will happen when I start sealing things up & properly insulating the place.
I agree that the foam expansion pressure is a big concern - I was eyeing up some of the so-called "minimally expanding" products that claim be compatible with the filling of wall cavities. Still makes me a guinea pig, though!
I think you're best off leaving the gap alone. Masonry walls always do let some moisture in, and for that reason have a space behund them to let the water drain out. Trap water, and all manner of troubles start.