What base do I need for a flexing plywood subfloor - to lay tile?

We used a large tile that has cracked. It’s a 2nd floor bath.

  3 answers
  • Dee Dee on Aug 20, 2018

    If you used plywood, as a subfloor, you probably did not put mortar under the entire tile. The air between the tile and thin set made it crack when you walked on it.

  • William William on Aug 20, 2018

    If the subfloor is flexing you may have some damage to the joists. I would cut out an inspection hole and check out what is going on.

  • Kelli L. Milligan Kelli L. Milligan on Aug 27, 2018

    The subfloor isn't thick enough. You don't want any bounce. Need at least 2 3/4 " plywood as a base.