Why Do Floor Tiles Crack?
Cracked floor tile is usually a sign that something caused the tile to move, flex, lose support, or experience more stress than it could handle. Sometimes the cause is as simple as dropping a heavy object, but when cracks begin appearing without an obvious impact, we start looking at what's happening underneath the tile.
One common cause is movement or cracking in the concrete slab. Concrete naturally expands, contracts, shrinks, and can develop cracks over time. If tile is installed directly over a crack without the appropriate preparation or crack-isolation system, movement in the concrete can transfer through the mortar and eventually show up as a crack in the tile or grout above it.
Another potential cause is poor mortar coverage underneath the tile. Tile needs adequate support from the setting material below it. If there are large voids underneath the tile, portions of it may be left unsupported. When enough pressure is applied to one of those areas—from furniture, foot traffic, equipment, or an impact—the tile can crack. Hollow-sounding tiles can sometimes be an indication of poor bonding or voids underneath, although a hollow sound by itself doesn't automatically tell us exactly what has happened.
For tile installed over a wood-framed floor, movement and deflection become especially important. The floor assembly needs to be sufficiently rigid and properly constructed for tile. If the subfloor flexes too much as people walk across it, that movement can stress the tile and grout until cracking develops.
Movement joints and expansion areas matter too. Large tile installations need room to accommodate normal movement in the building and flooring assembly. If movement is improperly restricted, that stress has to go somewhere and can eventually contribute to cracked grout, loose tile, or cracked tile.
Installation quality also plays a major role. The correct mortar needs to be selected for the tile and substrate, surfaces need to be properly prepared, mortar coverage needs to be adequate, and the installation needs to follow the requirements of the materials being used. Problems in any of these areas can reduce the life of the finished floor.
And sometimes, the tile simply gets damaged. Dropping a heavy or sharp object can crack even a properly installed tile. That doesn't necessarily mean there's anything wrong with the rest of the floor.
The location and pattern of the cracking can often give us clues. One isolated cracked tile after something heavy was dropped on it is very different from several tiles cracking along the same line. When cracks repeatedly follow a particular path, we'd be much more interested in determining what's happening underneath the tile before simply replacing the damaged pieces.
The important thing is not to assume that replacing a cracked tile fixes the problem. If the crack was caused by movement, poor support, or a problem with the substrate, installing another tile without addressing the underlying cause may eventually leave you with another cracked tile in exactly the same place.
Before repairing a cracking tile floor, the better question is: Why did it crack in the first place?
