There is a gap between the concrete floor and the foundation of my garage. It is filled with a material that is soft, you can poke it with a wooden skewer.

Picture here: https://ibb.co/xD8jH9c

What is this gap filled with exactly? What material is it?

Thank you!

  • If you want to cover that 1/2" gap to make it look better or clean up easier you can put down a thin layer of self-leveling polyurethane sealer.
    – Bryan R
    Commented May 26 at 1:50

1 Answer 1


It is closed cell Expansion material.

It was installed to give the two opposing slabs room to expand, while still keeping water out.

  • Thank you! And because it's there to keep the water out, the fact that it accumulated moisture is working as intended right? It looks wet across most of the garage. Thanks again.
    – elektrei
    Commented May 20 at 19:44
  • Some types are tar impregnated. You may have those. It is not unusual for them to look wet.
    – RMDman
    Commented May 20 at 21:02

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