As a carpenter, I don’t know much about concrete, but I have a waterproofing problem with my garage. Water comes through a thin crack through two adjacent slabs in the floor and also under the wall foundation, which sits on the floor slab. The wall foundation is about 6″ high concrete, on top of which sits wood-framed walls. The concrete surrounding the garage is the same level as the floor inside the garage, i.e., there’s no hydrostatic pressure from above. What would be the best system for sealing the cracks between the slab and the wall foundation and for sealing the cracks between the two floor slabs?
Edited 6/10/2006 8:53 pm ET by GordonVN
Replies
The root of the problem was that the concrete was not placed on a proper base. It should have been installed over stone, elevated above the surrounding grade even a little bit so no liquid water would come in contact with the underside of the slab.
On the exterior, UGL Drylock (the latex, not the oil based, version) applied carefully in two coats should do the trick. If you have any cracks they should be caulked first with a quality paintable caulk. The drylock can be painted over with an exterior water based paint to look like concrete if you don't like the color.
As for the cracks in the slab, a good commercial urethane caulk would be good. A masonry supply house would have it in the larger tubes with the wider nozzle that you might need. If the crack is larger than, say, ¼" then use foam backer rod first.
This is a good example of why sill seal should be used even in an unheated structure. The concrete stem wall is probably often damp, and that dampness would be carried to the framing. Even if the sill plate is pressure treated and won't rot, it will still carry the moisture to the studs. Sill seal acts as a capillary break and keeps the framing dryer.
Thanks for responding. I don't think I can get to the outside crack where the stem wall is on the slab because I think the pathway beside the garage has an additional cememt screed surface added to it. So I was hoping to get some solution for the inside joint where the stem wall sits on the slab. I did read on the web about a crystalline treatment that could be painted on pourous concrete, but I don't know if that would do for cracks. But they did suggest routing out the cracks 1/2" deep. I wonder if just caulking the crack with a sealant would work.However, I think your solution for the floor slab joint would probably work o.k. I'm sure this is a common problem because I've often seen it in garages in this area (San Francisco Bay Area) where they do leak during the winter rainy season.
Edited 6/11/2006 2:28 pm ET by GordonVN