Symptoms
- Visible cracks running along the grout lines
- Grout crumbling or coming out in small pieces
- Cracks concentrated near doorways or high-traffic areas
- Grout feels soft or powdery when scratched
Likely causes
- CommonNormal aging and shrinkage of groutGrout can develop hairline cracks over years, especially in high-movement areas.
- CommonSubstrate movement or flexIf the floor beneath flexes slightly, the rigid grout cracks before the more flexible tile does.
- PossibleGrout mixed or applied incorrectly during installationToo much water in the mix or poor curing can lead to early cracking.
- PossibleWater intrusion weakening the grout from belowChronic moisture can degrade grout from the underside over time.
What to do
- Use a grout saw or an oscillating multi-tool with a grout blade to rake out the cracked grout to a consistent depth.
- Vacuum out all dust and debris from the grout lines.
- Mix new grout to match the color and type (sanded or unsanded, matching the original joint width) of the existing grout.
- Apply the new grout with a rubber float, packing it fully into the joints at a diagonal angle to the tile lines.
- Wipe off excess grout with a damp sponge before it fully sets, rinsing the sponge frequently.
- Let the grout cure per the product's instructions, typically 24–72 hours, before getting it wet or walking heavily on it.
- Seal the new grout with a grout sealer once fully cured to help prevent future staining and moisture absorption.
Tools and parts
- Grout saw or oscillating tool
- Rubber grout float
- Sponge
- Bucket
Matching tile groutSearch: “matching tile grout sanded unsanded”
Grout sealerSearch: “grout sealer”
When to call a pro
Call a tile professional if cracking is widespread or recurring soon after regrouting, since it may point to a subfloor movement issue.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.