Q: I thoroughly enjoyed Tom Meehan’s article
Tiling With Limestone. My wife just purchased 520 sq. ft. of multicolored 12-in. by 12-in. slate tile that varies in thickness from 3/8 in. to 3/4 in. Can slate be used in a shower like limestone?
Doug House, Houston, TX
A:
Tom Meehan, a tile installer in Harwich Center, Massachusetts, replies: Using slate in a shower stall is not a common installation, but it certainly can be done. The layout of slate tiles is almost the same as limestone. Because slate can vary in color and in grain, make a point of opening all the boxes, and spend some time blending tiles in the most pleasing color pattern.
I would bed slate tile in a latex-modified thinset mortar. My biggest concern with the installation would be establishing a consistent 1/4-in. grout joint between the tiles. As you’ve noticed, slate tiles tend to differ slightly in size. And with the natural cleft of slate, there can be thickness variations in any given tile, which means that the edges of adjacent tiles may not be in the same plane, a condition I call lippage. A 1/4-in. grout joint makes it possible to contour the sanded, latex-modified grout to the high and low points of the tile in an attractive manner.
Another concern is that slate, unlike limestone and marble, requires a light acid wash after grouting and before sealing. Always test a small area first. I recommend leaving the acid wash to a professional tile installer or stonemason.
Once the slate is installed, grouted and acid-washed, it should be sealed thoroughly. First, I apply a coat of impregnator; I’ve had good luck with Miracle Sealants’ 511 impregnator (800-350-1901; www.miraclesealants.com). Next, I put on a finish coat of Miracle Sealants’ Mira Matte. Keep in mind that slate is made of countless thin layers of stone. From time to time, a piece of the face of the tile may peel or chip off.
But don’t worry; just reseal the newly exposed area.
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