I have an area underneath an egress window in the basement where the caulking has shrunk and the bare wood is exposed (see pictures below). I thought about backer rod and caulking the top and bottom, but the angle makes it impossible to caulk the top. Then it occurred to me to perhaps use the Great Stuff Window and Door expanding foam in the gap to seal it so water doesn't get to the wood.

Is there a better solution for this? I like the idea of foam as it expands to all the cracks, but not sure if there is a better solution out there. Pictures below...




1 Answer 1


Great Stuff foam will not last exposed to the elements and it's not water resistant it's mainly an air barrier. My suggestion is to cut a piece of treated lumber to fit space. It looks like a 2x4 will fit between sill and slab. It can be rip down to be flush with to outside edge of the sill. Run a good bead of caulking first to the inside then install board and finish sealing.

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