Cracked grout in a bathroom isn’t just ugly — it’s a slow leak waiting to happen. Water works its way through those cracks, gets behind the tile, soaks into the substrate, and eventually causes mold, rot, or tile failure. The fix is manageable if you catch it early. Here’s what you’re dealing with and how to handle it.
Why Does Grout Crack?
Grout is rigid. Houses move. That mismatch is the core of the problem. Specifically:
- Normal settling: Every house settles slightly over time, and that movement stresses rigid grout joints.
- Subfloor flex: Floor tiles are especially vulnerable. If the subfloor flexes when you walk on it, the grout will eventually crack.
- Poor original installation: Too little grout, wrong grout type for the joint width, or grouting over a damp surface all lead to early failure.
- Corners and edges: These areas move more than the field, which is why grout in corners almost always cracks first. (This is why corners should be caulked, not grouted — but many installers skip that step.)
Assess the Damage First
Press on the tiles near the cracked grout. Do they move? If tiles are loose or hollow-sounding when tapped, the adhesive behind them has failed and you may need to remove and reset tiles — a bigger job. If the tiles are solid but the grout is cracked, you’re in better shape.
How to Regrout a Section
What you’ll need: Grout saw or oscillating tool with grout removal blade, vacuum, sponge, matching grout, grout float, grout sealer.
- Use the grout saw to remove cracked grout to a depth of about 1/8 inch. Be careful not to chip the tile edges.
- Vacuum out all debris and wipe the joints clean.
- Mix grout per package directions until it’s the consistency of peanut butter.
- Apply with a grout float at a 45-degree angle, pressing firmly into joints.
- Wipe excess with a damp sponge before it hardens — this is time-sensitive.
- Let cure for 24–72 hours, then apply grout sealer.
Use Caulk in Corners
At inside corners and along the tub/tile seam, use color-matched silicone caulk instead of grout. Silicone is flexible and handles movement without cracking. This is the single most effective thing you can do to prevent repeat failures.
When to Call a Tile Contractor
If more than 20–30% of the grout is cracked, if tiles are loose, or if you see any soft or spongy substrate when tiles are removed, bring in a professional. Widespread grout failure usually signals a deeper waterproofing or substrate problem that needs to be fixed before new grout goes in.