I am replacing kitchen ceramic floor tile because the grout is coming out. The inspector says its because it's installed on 1/4 inch plywood instead of minimum 5/8 inch. I asked experienced tile guy who agreed. My problem is I am getting so many conflicting oppinions saying this is not true and just regrout the tile.

  • If you can get the joist depth, span, and spacing, we can tell you what the minimum plywood depth needs to be. Otherwise here's a useful guide: If your house was built after the 1980's, total of 5/8th (in two sheets) should be fine, 1940's to 1980's, would be more like 3/4 (again in two sheets), and anything older than that: 1 1/4" (two sheets). – Chris Sep 15 '16 at 13:03

The flooring or base below the tile is as important as the tile itself. If the floor flexes the tiles will break or pop loose the grout will crumble and come out. I like to add a cement backer board both glued and screwed to the decking. In the few cases I have used Plywood I also glue and screw it. This only takes a few minutes and it makes the base solid. With a solid base the tile will last longer. Not only by eliminating the cracking but when well laid tile over a solid base has something dropped on there is less chance the tile will break compared to a poor job. 1/4" is way thin even glued and screwed it would not hold up compared to 1/2". 5/8" would be better if using plywood. The best option in my opinion is 1/2" cement board the tile & grout will stick to this better than wood. If you have the floors redone Insist on a construction adhesive or thin set be used with screws to create a solid base the few extra dollars it cost up front will stop problems like you have now from happening in the future.


If you tap the tiles and they sound hollow, thin set is the problem, not being enough of it laid, or if the wood screws were not fastened all the way and it before install, that causes a bounce, and can also be the cause.

If those 2 are ruled out. It can be the wrong grout was used. Normally that points to using a sanded grout in gaps smaller than recommended use.

And if it is none of those things, it can be caused by what can not be tested or seen such as, if the tiler:

  • Doesn't wet the joints before applying the grout.
  • Doesn't mix the grout to a consistent, thick and creamy paste.
  • Doesn't fill the whole grout joint and compress the grout into the joint when grouting.
  • Uses old grout that is past its expiry date or shelf life.

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