On Dec 17, 5:49*pm, "Bob F" wrote:
RBnDFW wrote:
That's an interesting idea. I was concerned that the grout would pass
moisture.

If that's your issue, you could use epoxy grout.

Back in stone age, when we would use plywood in wet areas (like a
hanger board for wall-hung sink or towel bar), we would often paint
the plywood all six sides with epoxy before installing, like when you
are building a fiberglass boat and installing mounting pads. But that
was dfor mechanical fastening- dunno if thinset or mastic wil stick to
epoxy.

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