How to Lay a Stone Tile Floor
Use an uncoupling membrane to prevent tiles from cracking or popping loose
Q: We're remodeling our kitchen and want to install a stone-tile floor. Anything we need to know before we begin?
—Meghan Fouracer, Ithaca, N.Y.
A: If you're going directly over subfloor, tiles are likely to crack or pop loose unless you take two extra steps. First, stiffen the subfloor by gluing and screwing a second layer of ¾-inch sheathing to the existing layer. Second, install what's called an uncoupling membrane to isolate the rigid stone or ceramic from the subfloor's flexing joints and seasonal movements. Here, we used Ditra (schluter.com), a dimpled plastic sheet that resembles a thin orange waffle. Although many tilers still slap stone directly onto the subfloor, I won't guarantee any of my jobs without the membrane.
Once the membrane is cemented in place, the tiling proceeds as usual. Be sure to use unmodified thinset, as the latex-modified kind won't harden properly when sandwiched between the tile and the membrane.
Cut the Membrane
Starting in a corner, roll out the membrane, flocked-side down, beside the room's long wall. At the end wall, crease the roll into the corner, as shown, and cut along that crease with a utility knife. Trim as needed to get around pipes, ducts, and doorways. Lay out and cut the remaining sections so that their edges butt together and they cover the entire floor.