A loose floor tile that rocks or sounds hollow when tapped has lost its adhesive bond to the subfloor. Regluing it before it cracks or someone trips on it is a simple repair.
Slide a putty knife under the edge of the loose tile and gently pry it up working slowly around all four edges. Scrape all old adhesive off the subfloor and off the back of the tile. Both surfaces need to be clean and flat for the new adhesive to bond.
Inspect the subfloor for moisture or softness before regluing. Spread a thin even layer of tile adhesive on the subfloor and on the back of the tile. Press the tile firmly into place and align it with surrounding tiles. Put something heavy on top for 24 hours.
Once the adhesive has fully cured, mix grout to match the existing joints and apply it around all four edges. Press firmly with your finger or a grout float. Wipe excess grout off the tile surface with a damp sponge before it dries.
If the tile is cracked or chipped, regluing will hold it down but the crack will still be visible. Replace a cracked tile — see Page 22 for that process.