When I moved into my house, the kitchen has large floor tiles on the floor. Quite a few of these tiles are cracked. I've been told that the reason they are cracked is because under the floor tiles is a plywood underlay layer, and where the plywood pieces meet each other isn't exactly even, and so the tiles are cracking at that join.

If I was to pull up the tiles an lay a new floor, what would I have to do to overcome the uneven plywood flooring? Is there something I should lay on top? Or should the plywood be re-layed?



2 Answers 2


If the tiles are cracking, it's probably (edit: might not be) not just the plywood. The floor is flexing in some manner. Tiles need a very rock solid underlayment.

So pulling up the tiles and then pulling up the subfloor and then relaying a new subfloor may not actually fix your problem.

The joists may be flexing (and this is probably the issue) which would cause the floor to crack.

How old is the building? If the build is quite old, the joists may be further apart or sized smaller than current code.

There are a few solutions, once you determine the problem:

  • sistering the joists

  • adding cross joists under the existing joists

  • adding lolly columns under the floor

I fixed a floor on the third floor of a 100 year old house by pulling up the plywood and gluing and screwing half inch subfloor. The floor was rock solid, but we still didn't put back ceramic tile - we went for black and white vinyl. Looked great.


The plywood should be relaid so that it is even and you need to put half-inch concrete board on top of the plywood. Especially for larger tiles.

  • 1/2 CBU does not help with deflection for tiles (try picking up a 1/2 CBU board and notice how much it flexes). If the floor needs to be made stiffer adding CBU will not do it, you need to sister the joists or reinforce the subfloor with more/thicker layers of plywood/OSB.
    – auujay
    Apr 17, 2014 at 13:25
  • 1
    @auujay - he said his tiles are cracking because the subfloor isn't even. For all we know the plywood could be 3 inches thick. There is nothing in the question that infers flexing due to joist movement.
    – DMoore
    Apr 17, 2014 at 13:28
  • I guess I can't argue with that point. I just don't believe the OP really knows why the tiles are cracking.
    – auujay
    Apr 18, 2014 at 14:17
  • @auujay - not saying that you are wrong. But unless the OP has proven themselves incapable I usually just go with what they say. And when I offer advice I don't usually have them overdo everything (Mike Holmes style). I know that having uneven subfloor will cause cracking and he said those are the only places where it cracked. The concrete board will actually help with joist flexing if put down flat.
    – DMoore
    Apr 18, 2014 at 17:02

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