A hollow sound is not always a loose floor tile
A floor can sound hollow while the tile is still well bonded. The Tile Council FAQ says this shows up when a mortar bed has let go of the layer under it, or when the subfloor is too thin or poorly fastened. Systems that are built to separate the tile layer on purpose, such as a mortar bed over a cleavage membrane in handbook detail F111, need a closer look before a hollow tap is treated as debonding.
When a hollow spot is more serious
A hollow spot is not ideal, and it is not automatic proof that the floor is about to fail. Over concrete, with no bounce in the floor, grout and gravity can hold the assembly if movement joints are sufficient and shear is small. Over wood, movement in the subfloor is more likely to break grout away from the tile and make the floor less stable.
Other ways bond is lost
The same FAQ lists expansion without enough movement joints, weak thinset where shear is present, paint or sealer on the subfloor, moisture damage, too much deflection, thinset placed in dabs, thinset used past its working time, and adhesive that fails when it gets wet. Only an on-site inspection can sort those causes. A tap test alone does not name which one happened.
Source
Fetched 2026-10-11 from Tile Council hollow and loose tile FAQ. The sentences above follow that page. They are not a contractor promise.
Related notes
- Tile notes index
- Lippage is the step between adjoining tile edges
- Cracked floor grout often starts with movement
- Shower photos
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