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Community and Q&A

Sealing concrete foundation – foam insulation joints

dominic123 | Posted in General Questions on

Hello GBA Community – we poured concrete basement slabs about a week ago, with XPS installed vertically between the foundation walls and slab as a thermal break. The vapor barrier laps up between the wall and the XPS, though isn’t taped to the wall. Should I use a sealant or tape to ensure a continuous air barrier, and if so, does anyone recommend a good product that will adhere to both the concrete and XPS? It is a bit wet out, and we plan to install the XPS layer for the walls above this gap tomorrow, so I may miss the opportunity to seal this joint if the product needs to be applied to a dry surface. I’ve attached a photo to this note. Thanks!

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  1. dominic123 | | #1

    (we are in climate area 4C)

  2. GBA Editor
    Martin Holladay | | #2

    You don't have to seal this joint at this point. Just proceed with your plan to install rigid foam on the walls. After you install the XPS on the walls, you'll want to seal the XPS seams (with high quality tape, canned spray foam, or caulk). At that point, you can seal the horizontal crack at the base of the wall (the crack between the XPS on the wall and the concrete slab) with Siga Wigluv tape or caulk.

  3. dominic123 | | #3

    Thank you very much Martin.

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