A.Michael Byrne responds: "When" and "why"aren’t the only questions to ask — how about "where" and "what"? In particular, what kind of underlayment and surfacing materials have been selected for this installation? OSB should never be considered for any tile installation: Its expansion/contraction rate is so different from that of tile that this alone would rule out its use as a setting bed for tile. Besides that, in many controlled tests, OSB has proven to be so inadequate as a tile substrate that an industry installation standard has never been written for its use.

Having said that, I realize that OSB has been used with varying degrees of success. This often hinges on the condition of the OSB, the other materials involved in the installation, and "where" the tile is installed. If the OSB panels have been recently installed in a dry, stable environment over a sturdy plywood subfloor, and the...

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