I'm planning on redoing the flooring in a basement room which has a concrete slab in a 1974 Seattle house. The current carpet, which I've already removed, will be replaced with LVP.

After removing the carpet, I spotted a bunch of loose concrete around the edges of two exterior walls (it's a corner room). It appears that the previous owners tried to originally nail down the tack strips for the carpet too close to the edge of the concrete slab which must have resulted in it getting chipped off in large chunks. I've cleaned out the loose concrete but I'm now left with multiple large holes (as large as 1" x 3"). Any ideas on how I can fix these?

From what I've researched so far, I want to ensure that the expansion gap between the foundation and the concrete slab remains untouched.

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  • I'm not installing carpet, I'm installing LVP flooring. Everything I've read seems to indicate that you should fix your concrete up before you install LVP on it. This article claims that a 0.4" gap is by design: homearise.com/gap-between-slab-foundation-wall
    – K Mehta
    Commented Nov 16, 2021 at 16:01

2 Answers 2


put some paper or plastic sheet down the crack against the wall then fill the holes with leveling compound, or builders filler.

  • What's the plastic for?
    – isherwood
    Commented Nov 16, 2021 at 13:47
  • Cement doesn't stick to plastic IIRC so it acts as a removable barrier
    – K Mehta
    Commented Nov 16, 2021 at 15:58
  • yeah it's to stop the filler from foining the wall foundation to the slab, to allow for a little movement.
    – Jasen
    Commented Nov 17, 2021 at 4:43

It's not an issue. Once you leave the edge gap for your flooring it only spans maybe 3/4" over the voids for an inch or two. You'll never notice it.

If it bothers you, fill the voids with almost any cement patch you can find. Basement slabs don't typically get expansion joints. I don't see one here. There's evidence of slab shrinkage, which is normal during the cure, but there is no expansion material.

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