How thick should wood subfloor be and what size trowel?

QUESTION

How thick should the Wood Subfloor be for Tile and What Size Towel should be Used? - Could you help me with this? I am looking for the proper thickness of a plywood sub-floor on 19.2 inch centers for a large format tile. And what would be the proper trowel size for a 12 X 24 inch tile and also for a 18 X 36 inch tile. If you could help me with this that would be great.

ANSWER

ANSWER - There is a lot more to a proper configuration of a subfloor for tile than just the thickness of the subfloor. It is normally recommended to have at least 23/32" thick tongue and groove exterior glue plywood. That alone doesn't ensure adequate structural stability.

There are no requirements for what size trowel. The requirements are to achieve 95% thin-set contact with full contact at all edges and corners, is up to the person installing the tile to determine the means and methods for achieving it. There are different ways of achieving it. You can take the Tile Installers Thin-set Standards (ITS) Verification course for more info and details at https://uofcts.org/online-courses/titc-certified/.

2 thoughts on “How thick should wood subfloor be and what size trowel?

  1. Donato Pompo says:

    There are no requirements for what size trowel. The requirements are to achieve 95% thin-set contact with full contact at all edges and corners.

    For that size tile I would use a marble loop (u) trowel. First use the flat side of the trowel to key the thin-set into the back of the tile and into the substrate. Then use the notched side of the trowel to gauge how much thin-set to add. Depending on what angle you hold the trowel you will add more or less thin-set.

    You need to pull tiles immediately after initially installing them so you can verify that you achieved full thin-set contact. Fill in any areas where the trowel ridges did not collapse and re-install the tile.

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