As a tile contractor and consultant, I’ve had plenty of opportunity to observe failed tile installations. But I’m also aware of tile work that is centuries old and still looks fresh and new. Why? Maybe because most of the ancient tile work was done for pharaohs and kings, and the penalty for less than perfect craftsmanship was death. About the worst that can happen today is to have an installation red-flagged by the inspector. Most of the installation failures I’ve seen have resulted from a failure to follow directions. Whether the directions are in the form of specifications, industry recommendations, or the printed instructions on a container, failure to heed the advice will almost guarantee problems. Most contractors don’t intentionally ignore instructions, but they often fail to make themselves aware of the recommended methods. What follows are the instructions and recommendations most often ignored by tilesetters, and the problems that result.

Allowing for Movement

Probably 90% of the tile installation problems I’ve encountered are a result of the tilesetter failing to allow for substrate movement. Typical problem spots are vertical wall planes that intersect with horizontal surfaces, concrete substrates with control joints or random cracks, and the junctures of dissimilar materials. In these situations, a "movement joint" (my term for a broad class of expansion or control joints) should be used. Inside corners should be left free of grout, then caulked after the grout has cured. Use a high-quality silicone caulk, and install a foam backer rod in the open joint before caulking. It’s also important that all "hard" material be cleaned out of an open joint before caulking. Small bits of hardened adhesive or grout can apply point pressures to adjacent wall surfaces, causing cracks as the substrate expands. When installing tile over a concrete slab, creating movement joints can be a little trickier. One approach is to position an open tile joint directly above any slab joints, install backer rod, and caulk. The trouble with this approach is that the location of this open joint may disrupt a patterned tile layout, or you may be forced to follow a slab joint that is crooked or out of square. A more adaptable approach is to use a crack isolation membrane like the one manufactured by the Noble Company (614 Monroe St., Grand Haven, MI 49417-0350; 800/878-5788). Although its use will not completely eliminate cracks, the 1/32-inch membrane material isolates the tile from the substrate movement and allows tile movement joints to be located near the slab joint instead of directly over it. The width of the membrane should be three times the tile size, and it should be bonded to the slab using either Noble’s proprietary latex-based adhesive or an acrylic or polymeric modified thinset mortar (see Figure 1).

Figure 1. A tilesetter uses a floor roller to adhere a crack isolation membrane over a slab control joint. The membrane should be three times the width of the tile.

After the membrane is installed, the tile is bedded in thinset adhesive and two movement joints are located on either side of the slab joint (Figure 2).

Installing Isolation Membrane

Figure 2. Install an isolation membrane over slab cracks and control joints (top) and at the juncture of dissimilar materials (second). Use a movement joint on each side of the crack. In the case of diagonal tiles (third), use a zigzag movement joint. For random cracks (bottom), movement joints should be located on both sides, following the direction of the crack. When the slab joint is covered by angled pattern tile, the movement joint is zig-zagged over the slab joint. This isolation membrane is also ideal for bridging random slab cracks (a difficult item to work into a tile pattern) and joints created when two dissimilar substrates meet. The same ratio of membrane width to tile size applies, and movement joints must be located on either side of the random slab crack. Unless you’re using a white grout, you may have difficulty finding an off-the-shelf caulk for the movement joint that matches the grout color. Color Caulk (723 W. Mill St., San Bernardino, CA 92410; 909/888-6225) carries an inventory of colored and sanded caulks that will match just about any manufactured grout on the market.