I recently removed ceramic tile off of my concrete subfloor (installed by the previous owner) and wherever the subfloor meets an exterior wall of the house, there is a 0.5-2" gap of missing subfloor. This is the case around the entire perimeter of the house, not just one wall or section. I was planning on filling this in with some SLU that says it will work with applications up to 2" thick in preparation for re-tiling but now I am wondering if that is the best solution. I tried searching for similar damage online, but I couldn't find anything similar. What is going on here and how do I best repair this?

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  • just fill it up with sand, to allow movement and settlement between subfloor and the foundation
    – Traveler
    Jul 6, 2022 at 19:21
  • That's (mostly) not damage, that's a concrete slab poured with expansion joints where it meets the concrete walls. You can see the joint material in the last picture. The 1/2" is intentional, the places where it got chipped much wider (probably in removing the tile) are "damage."
    – Ecnerwal
    Jul 6, 2022 at 19:37

1 Answer 1


You have a floating subfloor, which is good to avoid cracks.

It was installed with a gap on purpose, so not to touch the foundation.

The gap is usually 1/2 inch wide.

What ever you do, do not fill it with SLU or similar concrete products.

If you want to fill it, use backers rood.

You can then repair the chipped of parts.

  • Thanks. Can I use some kind of rigid plastic backing and some quickcrete (thicker consistency than SLU) to fill in the chipped part without filling in the gap between the slab and the foundation? I am worried if I don't fill in the chipped parts that the tile will not have enough support and could pop up
    – Palin567
    Jul 6, 2022 at 21:07
  • Thank you for finding my answer useful. You can do that. Know that concreted does not stick to concrete very well, so use concrete primer (liquid)
    – Traveler
    Jul 6, 2022 at 21:13

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