If the tile is moving in and of itself, the grout lines will generally crack and pop loose. Tile movement could be due to improper support of the tile by the mortar bed, or lack of proper notch trowel to include improper back buttering the tile before setting into the thin-set mortar. This is usually identified with a hollow sound in and around the problem area, using the tried and true screwdriver handle tap test.
If the subfloor is moving, the movement is transmitted through the tile and manifesting itself as surface cracks in the tile and generally not following the grout lines. Without removing the tile in the affected areas, we can only speculate (based on past experience) what the cause is! But it’s fun to speculate! Wall Street has been doing it for years. It makes us play other fun games like “What If” and “Cause and Effect.”
Photos 1a and 2 show a typical thin line crack in a low-traffic area, with Photo 1b showing a close-up of the cavity. The crack is in somewhat of a straight line and passes through several tiles. Could this be a saw cut telegraphing due to improper prep of the saw cut? “You Make the Call.”
Photos 3 and 5 are in high-traffic areas and have more of a multi-fracture appearance. Photo 4 is a close-up of the higher-traffic cracks. Also visible in Photo 3 is the lack of metal on the tile’s edge where it meets the carpet. Without it the carpet will eventually matt down, exposing the tiles edge to the vacuum sweeper, and chipping along the entire edge will take place.