Tile cracks are the slab underneath showing through.

Cracks in Floor Tiles and Grout: diagnosed and explained.

A crack that runs across several tiles in a line usually means the concrete slab beneath them has cracked or moved. Tile is the least forgiving floor covering you can put over concrete, which makes it the most informative. Porcelain and ceramic have almost no ability to bend, so when the slab beneath them flexes, cracks, or tilts, the tile answers immediately: a crack running through several tiles in a line, grout joints crumbling or separating along a path, tiles that sound hollow when tapped, or a corner of the floor where lippage has appeared, one tile edge sitting higher than its neighbor. The pattern is the diagnosis. A single cracked tile with intact neighbors usually took an impact or was installed over a small defect. A crack that travels across multiple tiles in a continuous line is telegraphing a crack in the slab below, because the tile is reproducing what the concrete under it did. Slabs crack and tilt when the soil beneath them moves, and in Southern California, Arizona, and Nevada that usually means expansive clay shrinking away from the slab in the dry season and swelling back in the wet one, a plumbing leak eroding support, or fill soil still compressing. Grout tells the same story earlier and more cheaply: grout lines that keep cracking along the same path after regrouting are marking a live joint in the slab. Before regrouting a third time, it is worth finding out what the concrete is doing.

For the repair side of this, the foundation repair solutions page lists every method Dalinghaus installs, including the ones that fix problems other than cracks in floor tiles and grout.