Symptoms
- Visible hairline or wider cracks between tiles
- Grout crumbles when scratched
- Cracks concentrated in corners or along the tub edge
- Tiles otherwise feel solid
Likely causes
- CommonNormal aging and shrinkage of groutGrout is porous and becomes brittle with age and repeated wetting and drying.
- CommonGrout used in a corner or expansion joint instead of caulkRigid grout cracks where tile surfaces meet at an angle and need to flex slightly.
- PossibleWater intrusion behind tile weakening the bondLong-term leaks can soften the backer board, causing tiles to shift and grout to crack.
- Less commonStructural movement or a loose subfloorWidespread cracking across many tiles can indicate the wall or floor structure is flexing.
What to do
- Press gently on tiles near the cracks; if any feel loose or hollow-sounding when tapped, treat this as a bigger repair, not just grout.
- Use a grout saw or oscillating tool to remove the cracked grout to a consistent depth of about 1/8 inch.
- Vacuum out all dust and debris from the grout lines.
- Mix new grout matching the existing color and press it into the joints with a rubber float, working diagonally across the lines.
- Wipe off excess grout with a damp sponge after about 15–20 minutes, rinsing the sponge frequently.
- Let the grout cure per the product instructions, typically 24–72 hours, before it gets wet again.
- Seal the new grout once fully cured to help resist future water absorption.
Tools and parts
- Grout saw or oscillating tool
- Rubber grout float
- Sponge
- Vacuum
Sanded grout matching tile colorSearch: “sanded tile grout”
When to call a pro
Call a tile contractor if tiles feel loose or hollow, or if cracking is widespread, since it may mean the wall behind is damaged.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.