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Old 09-27-2011, 03:09 PM   #5
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Join Date: Sep 2011
Location: Anacortes, Washington
Posts: 138
OK, and not to belabor the point, but is using backerboard and Kerdi still a viable option in this situation? If it is, it seems like 1/2" fiber cement board could offer benefits in contact with the heating wires due to it's higher thermal conductivity which would minimize temperature gradients in the tile/grout layer as well as in the subfloor. The reason this is of even a concern is the bathroom is in a ski cabin which is mostly unheated when it is not occupied and will be cranked up upon arrival. Also, the heating is by loose wire and I want to use a fairly dense pattern as I have removed the electric baseboard.

And I realize this will not be ultimately as stiff as two layers of plywood but, given the narrowness of the room and it's location on the foundation I'm not sure this is an issue.

As a side note, the tile installer I met said he had always put the heating wire set in thinset on top of Ditra and was surprised when I mentioned the Ditra Booklet calls for the wire to go underneath. Anyone have the pros/cons of the two methods?
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