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I have a basement finishing company who will be installing spray foam directly to my cinder block foundation wall. I have an interior French drain and I’m worried how the spray foam will affect the drain. The foam will cover the dimple board that comes about 4 inches out of the floor and it will also cover the 1/2 inch gap between the dimple board and the wall. I’m worried water coming in from the wall will not find its way down the wall and into the drain since the foam will effectively block the water from coming through the wall. Question is, where does the water now go? Does is it sit in my wall until it dissipates or can be absorbed back into the ground outside or does it break through the foam eventually (via hydrostatic pressure) and go onto the floor since it can not drain behind the dimple board? Anyone ever done this before and if so what were your results? Thank you!

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If water is traveling horizontally through your wall, it can also travel vertically through your wall. So, the area behind the dimple board should still be available to accept water coming out of the wall, rather than the hypothetical you've through up where the water is totally blocked by the foam and can't escape - unless your contractor is an idiot who's going to sprayfoam behind the dimple board.

If your wall leaks badly, you might want to extend the dimple board prior to adding insulation - foam is unlikely to stick all that well to a wall that is constantly wet, and more direct access to the drainage for the water coming in will help to avoid potential issues with water delaminating the foam.

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