Tile Grout Cracking: Why It Happens & How to Repair It
Cracked grout between tiles is usually caused by settling, moisture infiltration, or age-related shrinkage. Left unrepaired, cracks allow water to seep behind tiles and cause mold, rot, or structural damage—repairs can cost $500 to $2,000 if water damage develops. A DIY grout repair involves removing the damaged grout, cleaning the joint, and applying new grout and sealer, typically costing $20 to $50 in materials.
Step-by-Step Fix
- 1
Assess the damage
Examine all grout lines for cracks wider than 1/8 inch or discoloration that indicates water damage. Tap tiles near cracks with a rubber mallet to check for hollow spots, which mean moisture has gotten behind the tile. Mark areas that need repair with painter's tape so you don't miss any spots.
- 2
Remove the old grout
Use a grout saw or oscillating tool with a grout blade to cut out cracked grout at least 1/4 inch deep. Work at a 45-degree angle and move slowly to avoid chipping the tiles. Vacuum out all dust and debris from the joint so new grout adheres properly.
- 3
Clean and dry the joints
Wipe the cleaned grout lines with a damp sponge to remove remaining dust, then let them dry completely for at least 2 hours. Do not apply new grout to wet joints, as this weakens the bond and causes premature failure. Use a heat gun or hair dryer to speed drying in humid bathrooms or kitchens.
- 4
Mix and apply new grout
Mix unsanded grout (for joints 1/8 inch or smaller) or sanded grout (for joints larger than 1/8 inch) to a peanut butter consistency. Load a grout float and press grout firmly into the joint at a 45-degree angle, overfilling slightly. Work in small sections so the grout doesn't dry before you finish.
- 5
Tool and clean the joints
After 10 to 15 minutes, when grout becomes firm but not hard, use a grout sponge or wet cloth to clean excess grout from the tile surface. Smooth the joint with a rounded tool or your finger for a professional look. Let grout cure for 48 to 72 hours before exposing it to moisture.
- 6
Seal the grout
Apply a penetrating grout sealer 72 hours after grouting to protect against stains and water infiltration. Use a small brush or applicator bottle to coat only the grout lines, wiping excess from tiles immediately. Reapply sealer every 1 to 3 years depending on traffic and moisture exposure.
⚠️ Safety Notes
- Wear a dust mask and safety glasses when cutting out old grout, as silica dust can damage your lungs.
- Do not expose new grout to water for at least 48 hours; moisture during cure time reduces strength by up to 30 percent.
- If you find soft or crumbling substrate behind the tile after removing grout, call a professional—this indicates structural damage that DIY repair cannot fix.
When to Call a Pro
Call a professional if grout cracks reappear within 6 months, if the substrate behind tiles feels soft or spongy, or if you see signs of widespread water damage such as dark stains, mold, or tiles that rock when pressed.
Frequently Asked Questions
- Can I use caulk instead of grout to repair cracks?
- No—caulk is flexible and does not harden like grout, so it fails quickly in high-traffic areas. Use urethane or silicone caulk only for expansion joints at corners or edges where slight movement is expected; use grout for regular tile joints.
- How deep should I cut out the old grout?
- Cut out old grout at least 1/4 inch deep, or one-third the width of the joint. Deeper removal ensures new grout bonds properly and reduces the chance of the same crack reappearing.
- What's the difference between sanded and unsanded grout?
- Unsanded grout works for joints 1/8 inch or smaller and resists shrinking; sanded grout is best for joints larger than 1/8 inch and is more durable under traffic. Using the wrong type leads to cracking or sand falling out of joints.
- Do I need to seal grout after repair?
- Yes—sealing within 72 hours of grouting protects against water and stains, and extends grout life by years. Unsealed grout absorbs water, which causes mold and re-cracking.
- Why does grout crack after I repair it?
- Grout cracks if it's mixed too wet, applied to wet joints, or exposed to water before curing. It can also crack if the underlying tile or substrate has shifted; if cracks return quickly, the root cause is structural movement, not poor grouting.
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