I was removing old tile from my kitchen and found the crack seen in the pictures. I was wondering how big a deal the crack was and how to proceed with trying to lay new tile. I wanted to knock out more of the thinset mortar left around it, but I was afraid I might make the crack worse. Any advice on how to go forward?

Pic 1 Pic 2 Pic 3

  • is this slab on grade or concrete/thinset over subfloor? Mar 7, 2021 at 4:19
  • This is over subfloor. The house is on pier and beam so no concrete slab Mar 7, 2021 at 4:22

1 Answer 1


You'll need to lay down an isolation pad over the crack before installing the new tile.

The pad will allow the crack to open (if it is active) and not break the tile like as if they were set directly to the concrete floor.

  • Thanks! Would I just need to put an isolation pad over the cracked area or other parts as well? And am I okay to chisel away the thinset mortar around the crack or does that risk making it bigger? Mar 7, 2021 at 2:04
  • If, while you are chiseling around the crack while removing the old thinset and more pops out than expected, you can fill it in with thinset either before you lay the isolation membrane and let it harden, or let the thinset that goes under the isolation membrane do the filling as you lay the membrane.
    – Jack
    Mar 7, 2021 at 2:53
  • If you feel that cracks may appear in the future than it would be wise to cover the entire floor with a pad..
    – ojait
    Mar 7, 2021 at 19:32

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