Q: I'm redoing a bathroom, using 12-inch-square tiles on the countertops. My tile installer refuses to use these same tiles in the shower, though, saying they are too heavy. He's afraid that water will soak through the grout and dissolve the mastic underneath, causing the tiles to fall. I'm quite familiar with the use of thickened marine epoxy on boats, so I thought I'd use that to secure the tiles. Any thoughts?

— Bruce, Dresden, Maine

A: Joe Ferrante replies: Perhaps your contractor has had problems in the past with tiles falling off shower-stall walls. It's true that moisture can migrate through grout and soften up some mastics enough to reduce their grip. But that doesn't mean that epoxy is the way to go: The stuff is expensive and not fun to work with.

For a more suitable tile adhesive, use a thinset mortar blended with a latex-modified mixing additive. Thinset is durable, relatively inexpensive, easy to apply, strong, and impervious to moisture. Applied to cement backer board, it'll hold up any tile you're planning to use, even if you wanted to tile the ceiling. I've put all sorts of tiles on ceilings, including granite and even concrete, and have yet to see one come down.

In shower stalls and tub surrounds — anyplace that's often wet — I'll skim the walls first with a thin coat of thinset, using a flat trowel to force it into all the joints. Then I'll come back the next day to lay the tile, bedding it in more thinset, spread this time with a notched trowel. An unusually heavy tile might need spacers to support it on the wall, or long sticks to hold it against the ceiling while the mortar sets, but there's no reason not to put tile up there.

If I were to guess, I'd bet your contractor just doesn't want to do the job. Saying tile is too heavy to set is like saying he can't do the work because he doesn't like the color.

(Joe Ferrante, a tiling contractor in Medford, Massachusetts, has worked on several This Old House TV projects.)
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