How to Repair Cracked or Crumbling Grout
Updated September 18, 2026
Can I do this myself?
Safe to DIY
Yes, regrouting is a safe and satisfying DIY job. Wear eye protection and a dust mask when removing old grout. Loose, hollow-sounding tiles or a soft floor point to water damage underneath and need a professional.
Grout fills the gaps between tiles, locks them in place, and keeps water and dirt out from underneath. When it cracks, crumbles or falls out, water can seep behind the tiles and into the floor or wall, which over time leads to loose tiles, mould and rot. Fixing damaged grout early is one of the best ways to protect a bathroom or kitchen floor.
The repair is simple in principle: remove the damaged grout, mix and press in new grout, clean the tile faces, let it cure, and seal it. The main choices are which grout to use (sanded for wider joints, unsanded for narrow ones, and epoxy for very wet or stain-prone areas) and how much to remove. Small cracked sections can be patched, but widespread cracking usually means regrouting the whole area.
Before you start, press and tap the tiles around the cracked grout. Cracked grout on its own is a common wear issue. Tiles that move, sound hollow, or a floor that feels soft underfoot, usually mean water damage or movement below the tiles. Regrouting won’t fix that; it needs a professional.
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Signs of the problem
- Hairline or wide cracks in the grout lines
- Grout crumbling, powdery or missing between tiles
- Dark stains or mould in grout lines that won’t clean
- Water seeping or staying dark in grout long after showering
- Tiles rocking or sounding hollow when tapped (a more serious sign)
Common causes
Age and wear
Most commonCement-based grout is porous. After years of foot traffic, cleaning and moisture, it can erode, crack and crumble, especially in high-traffic floors and wet areas.
Wrong grout or mix
Most commonUsing unsanded grout in wide joints, adding too much water, or not letting grout cure properly makes it weak and prone to shrinkage cracks.
Harsh cleaning products
SometimesStrong acidic or bleach-based cleaners gradually dissolve cement grout. Scrubbing with hard brushes wears it down further.
Floor movement
SometimesA timber subfloor that flexes, or seasonal expansion, puts stress on rigid grout lines. Cracks that follow straight lines across the floor, or return quickly after repair, often come from movement.
Water damage under the tiles
Less commonLeaks from showers, toilets or pipes can soak the subfloor or backing, loosening tile adhesive. The tiles then move and crack the grout. This needs finding and fixing before any regrouting.
Safety first: before you start
- Critical:Wear safety glasses when removing grout. Grout chips and dust fly out, and tile edges can chip.
- Critical:Wear an N95/FFP2 dust mask when removing old grout and mixing powder. Cement and sand dust contain crystalline silica, which is harmful to breathe.
- Wear gloves when mixing and applying grout. Wet cement is alkaline and can burn skin with prolonged contact.
- If using an oscillating tool, keep both hands on the tool, keep power cords out of water, and use a GFCI/RCD-protected outlet in bathrooms.
- Ventilate the room when using sealers or cleaning products, and never mix bleach with acid or ammonia cleaners.
- In older homes, tile adhesive and flooring below tiles may contain asbestos. Don’t lift tiles or grind adhesive without testing.
Tools & materials
Tools
- Manual grout saw or carbide grout scraper (or oscillating tool with a grout blade)
- Rubber grout float
- Large grout sponge and two buckets
- Margin trowel or putty knife for mixing
- Vacuum
- Safety glasses, N95/FFP2 dust mask and gloves
Materials
- Grout: sanded for joints over about 3 mm (1/8 in), unsanded for narrower joints, or epoxy grout for wet areas
- Clean water for mixing (follow the product’s ratio)
- Penetrating grout sealer (for cement-based grout)
- Flexible silicone sealant (for corners and changes of plane)
- Soft cloths
Step-by-step fix
- 1
Check the tiles first
Press on each tile around the damaged grout and tap it gently with the handle of a screwdriver. A solid click is good. A hollow sound, rocking tile or soft spot means the tile has lost its bond, often from water. Loose tiles must be reset before regrouting, and widespread hollowness needs a professional.
- 2
Remove the damaged grout
Using a grout saw or scraper, carefully remove the old grout to at least two-thirds of the tile depth, or at least 2-3 mm (1/8 in), so the new grout has room to grip. Work along the line with short strokes, keeping the blade straight to avoid chipping tile edges. For larger areas, an oscillating tool with a grout blade speeds things up.
Warning: Wear safety glasses and a dust mask. Go slowly near tile edges; glazed tiles chip easily.
- 3
Clean out the joints
Vacuum the joints thoroughly, then wipe with a damp sponge to remove dust. The joints should be clean and slightly damp, but with no standing water, before grouting.
- 4
Choose the right grout
Use sanded grout for joints wider than about 3 mm (1/8 in); the sand makes it strong and less likely to shrink. Use unsanded grout for narrow joints and on delicate tiles such as polished marble or glass, which sand can scratch. Epoxy grout resists stains and water best but sets fast and is harder to work with. Match the colour to existing grout if patching.
- 5
Mix the grout
Pour clean water into a bucket first, then add powder gradually, stirring until it reaches a thick paste like peanut butter, following the product’s ratio. Let it rest (slake) for the time on the label, then mix again briefly. Mix only what you can use in about 20-30 minutes.
Tip: Too much water makes weak grout that cracks and looks blotchy. Measure carefully rather than adding water to loosen it.
- 6
Apply the grout
Scoop grout onto the tiles and hold the rubber float at about 45 degrees. Press grout firmly into the joints, working diagonally across the lines so the float doesn’t dig in. Then scrape off excess by holding the float nearly upright and dragging diagonally.
- 7
Clean the tile faces
Wait until the grout is firm to the touch (often 15-30 minutes, check the label). Wipe diagonally with a well-wrung damp sponge to clean haze from tile faces and smooth the joints. Rinse the sponge often. When dry, buff off the remaining haze with a soft cloth.
- 8
Let it cure
Keep the area dry and avoid walking on it for the time on the product, often at least 24 hours for light use and about 72 hours before showers or wet cleaning. Cement grout usually needs to cure for a few days before sealing.
- 9
Seal the grout and corners
Once cured, apply a penetrating grout sealer along the joints with a small brush or applicator, and wipe off any on the tiles. Use flexible silicone sealant, not grout, in corners, at the edges of tubs and where floors meet walls, since these joints move.
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How to check it's fixed
- Grout lines are full, smooth and level with no gaps or pinholes
- Tiles are solid and don’t move or sound hollow
- Water beads on the sealed grout instead of soaking in
- No new cracks appear after a few weeks of use
When to stop and call a professional
- Tiles are loose, hollow-sounding over a large area, or lift easily
- The floor feels soft or spongy, or there are stains on the ceiling below
- Mould keeps coming back behind or under tiles, or there’s a musty smell
- Cracks run through tiles as well as grout, or reappear quickly along a line
- You suspect asbestos in old tile adhesive or flooring
How to prevent it
- Seal cement-based grout after installation and reseal about once a year in wet areas.
- Clean with pH-neutral cleaners and a soft brush, avoiding strong acids or bleach.
- Squeegee or wipe down shower tiles after use to reduce moisture and mould.
- Fix leaks and failing silicone around tubs and showers promptly.
Frequently asked questions
Sanded or unsanded grout: which should I use?
Sanded grout for joints wider than about 3 mm (1/8 in), because the sand prevents shrinking and cracking. Unsanded grout for narrower joints and for delicate tiles like polished marble or glass that sand could scratch.
Can I put new grout over old grout?
Not usually. A thin layer won’t bond well and will crack or flake off. Remove at least 2-3 mm (1/8 in) of the old grout so the new grout has depth to hold onto.
How long does grout take to dry?
Most cement grout can take light foot traffic after about 24 hours, but needs about 72 hours before heavy use or getting wet, and a few days before sealing. Check the product label.
Do I need to seal grout?
Cement-based grout is porous, so sealing helps it resist water and stains. Epoxy grout doesn’t need sealing. Reseal cement grout about once a year in wet areas.
Does cracked grout mean water damage?
Not necessarily; it’s often just wear. But if tiles sound hollow, move, or the floor feels soft, water may have got underneath. Get that checked before regrouting.
This guide is general information, not professional advice. Homes differ, so follow your product manuals and local codes. If anything looks different from what's described, or you feel unsure, stop and call a qualified professional. In an emergency, leave the area and call your local emergency number.
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