Bathroom tile grout cracking
moderate 2–5 h
Tools: grout saw or oscillating tool with a grout blade, vacuum, grout float, sponges and bucket, caulk gun, utility knife · Materials: sanded or unsanded grout matching the joint width, 100 % silicone bathroom caulk, grout sealer, mould cleaner
Steps
- Tap each tile around the cracked grout: a hollow sound or a tile that rocks means the tile is loose and needs re-setting, not just regrouting.
- Check the corners and the joint where tile meets the tub: those must be flexible caulk, not grout — grout in a corner always cracks.
- Cut out the cracked grout to at least two-thirds of its depth with a grout saw, vacuum the dust, and clean any dark mould with a mould cleaner; let it dry overnight.
- Mix grout to a peanut-butter consistency, press it into the joints diagonally with a float, and wipe the haze off with a damp sponge in two passes 15 minutes apart.
- Wait 48–72 hours, then seal the grout, and caulk every corner and the tub or shower-tray joint with 100 % silicone.
- Keep the shower dry for 24 hours after caulking and run the exhaust fan after every shower from now on.
Stop and call a pro if
- several tiles are loose or the wall flexes when pressed — the backing board is wet
- there is a water stain on the ceiling below the bathroom
- the grout is cracking in a straight line across the room and the floor slopes — that is movement, not wear
What a pro does that you can't
A tile contractor re-sets loose tiles on a fresh bed, replaces water-damaged backing board behind the shower, and rebuilds the corners with proper movement joints so the cracks do not come back.
DIY cost: $25–60 in grout, caulk and sealer