How do I keep tile from cracking?

Most tile cracking is decided before the first tile is set. A floor stiff enough for the tile, a membrane over substrates that move, full mortar coverage and flexible joints at the edges prevent most of it. For tile already in place, the work is simpler: keep hard impacts off it, keep the joints at walls and tubs flexible, fix leaks quickly, and keep spare tiles so a cracked one can be swapped without a visible patch.

Looking after tile you already have

Keep the edges flexible. Tile, grout and the floor under them move with temperature and humidity, and the edges are where that movement goes. Custom's grout data sheet says movement joints are required for perimeters and other changes of plane in all installations,^[2] and that cement grout is not for use in them.^[2] If the joint where your floor meets the tub, or your backsplash meets the countertop, is packed with hard grout, raking it out and caulking it is one of the cheapest ways to protect the tile.

Use a sealant that can move. For movement joints, ANSI's tile installation standard recommends a silicone, polysulfide or polyurethane caulk that meets ASTM C920.^[1] Custom's paper points out that low-cost siliconized acrylics do not meet ASTM C920 or perform as a movement joint in most specified tile installations,^[1] and notes that ANSI and TCNA recommend a caulk with a Shore A hardness greater than 35 for traffic areas.^[1] It also says an interior movement joint can usually be as wide as the grout joint, but never less than 1/8 inch.^[1] When a bead splits or pulls away, cut it out and redo it; see why caulk keeps cracking and how to recaulk a bathtub.

Think about sun. The same paper notes that floors in direct sunlight need movement joints every 8 to 12 feet,^[1] so a sunroom or a floor below a large window deserves a look if cracks show up there first.

Spread the load. Felt or rubber pads under chair legs, and plywood or hardboard sheets under a refrigerator or piano when it is moved, keep weight off tile edges and corners. A dropped cast-iron pan or tool can crack a tile outright, so a rug where you work at the counter is cheap insurance.

Keep spares. Daltile recommends buying about 10% more tile than you need and storing it^[8] so a repair matches. If you are moving into a house with tile, ask the seller whether any leftover boxes are in the garage or attic.

Keep water out of the subfloor. On a wood floor, Custom's plywood bulletin calls for all wood subfloors and joists to be dry before tile goes down, because any shrinkage afterward will result in bond failure.^[4] A dripping toilet seal or a leaking dishwasher can wet the wood from below. Fix leaks quickly and dry the area.

Check the grout seal. Sealing does not stop cracks, but it keeps grout resisting water and stains. Daltile's test is a few drops of water: "If the water droplets bead up, the sealant is fine."^[8] If the water soaks in, it is time to reseal.

Getting it right when tile goes in

If you are tiling a room or redoing one, these are the questions that prevent cracks. Most of them are invisible once the tile is down.

Is the floor stiff enough? Custom notes that building codes recommend floor deflection of no more than L/360,^[3] and that the Marble Institute of America recommends no more than L/720 for soft, large, heavily veined or thin stone.^[3] For tile bonded over a plywood floor, Custom's bulletin describes a subfloor at least 5/8 inch thick on joists 16 inches apart, plus a 3/8-inch exterior-grade plywood overlay,^[4] with 1/8-inch gaps between the panels and 1/4 inch where they meet walls and other fixed surfaces.^[4] It also says OSB, particle board, luan and interior-grade plywood are not suitable for bonding tile directly.^[4] If the floor bounces, stiffening it is structural work for a builder, not the tile setter.

Is there a membrane where it is needed? Crack isolation and anti-fracture membranes are designed to isolate tile and stone from minor in-plane cracking in the substrate.^[7] Custom explains that uncoupling mats absorb stress from movement in the floor below,^[5] and that its own mat can be used over young concrete and over single-layer plywood on joists up to 19.2 inches apart.^[5] Over a slab with cracks or joints, ask which one the installer plans to use and where.

Has the concrete cured? Most makers of tile-setting products require concrete to cure 28 days before tile is bonded directly to it,^[5] unless an uncoupling method made for young concrete is used.

Where will the movement joints go? Ask the installer to show you on a plan: around the room, at changes of plane, over joints in the slab, and through large or sunny floors.

Will the tile be fully bedded? Custom lists a recommended minimum of 80% mortar coverage in dry areas and 95% in wet areas and exteriors.^[6] Ask how the installer checks it, for example by lifting a freshly set tile to look at the back.

Is the layout right for the tile? For long tiles, Daltile says rectangular porcelain should not be set in a running bond pattern, but with no more than a 1/3 overlap.^[9]

Stop and call a pro if

• New cracks keep appearing, especially in lines across several tiles, or the floor bounces or sags.
• Tiles that used to sound solid now sound hollow over a growing area.
• You find water damage, soft wood or sagging joists under a tiled floor.
• Grout or tile is cracking in a shower, which can let water into the wall.

For the causes in more detail, see why floor tiles crack; for a single broken tile, see how to replace a cracked tile. Browse tile and backsplash work, find flooring businesses around Blacksburg, or read the other handyman answers.

When you need a hand, describe the tile repair once and local businesses quote it.