Cracked, powdery, or missing grout is not just ugly — it is an open door for water to get under your tile, and on floors it lets tiles rock and eventually pop. The good news: grout repair is one of the most DIY-friendly tile jobs there is, usually $20 to $40 in materials for a typical bathroom. The bad news: most repairs I get called to redo failed because someone smeared new grout over old without removing anything, or grouted a joint that should have been caulked. Let me walk you through diagnosing why the grout failed, then fixing it so it stays fixed.
Part of our Tile & Grout guide — explore the full guide →
First, Diagnose Why the Grout Failed
New grout over an unsolved problem fails on the same schedule as the old grout. Match the symptom to the cause before you buy anything:
- Hairline cracks along many joints — usually normal structural movement or grout that was mixed too wet originally. Repairable joint by joint.
- Cracks concentrated at wall corners, tub edges, and floor perimeters — these are change-of-plane joints that move. Grout will always crack here. The correct repair is flexible caulk, not more grout.
- Powdery, crumbling grout you can scratch out with a fingernail — weak original mix (too much water) or old age. Remove and regrout; a surface repair will not hold.
- Grout cracking plus loose or hollow-sounding tiles — the substrate is flexing or the tile bond has failed. Tap tiles around the damage; a hollow “thock” means the tile must be re-set first. Grouting a loose tile is wasted effort.
- A crack running in a straight line across multiple tiles and joints — the slab or subfloor cracked beneath. This needs a movement joint or professional attention, not cosmetic grout.
Tools and Materials
- Grout removal tool: carbide-tipped hand saw ($8–$12) for small jobs, or an oscillating multi-tool with a grout-removal blade ($20–$30 for the blade) for anything over a few feet.
- Vacuum, stiff brush, utility knife.
- Matching grout — sanded for joints 1/8 inch and wider, unsanded for narrower. A 1 lb repair box is $5–$8; a 10 lb bag is $12–$18. Pre-mixed acrylic grout in a tub ($15–$25) is convenient for small repairs and color-consistent.
- Grout float, sponge, two buckets, and painter’s tape if you are working next to fixtures.
- Color-matched siliconized or 100% silicone caulk for movement joints ($6–$10).
Matching the Grout Color (The Step Everyone Botches)
Grout color is the difference between an invisible repair and a patchwork quilt. Three realities to work with: existing grout is dirtier and often lighter or darker than its original chip; new grout dries lighter than it looks wet; and even the correct color reads different next to 10-year-old joints. My approach: deep-clean the surrounding grout first so you are matching its true color, then buy the closest chip and mix a small test batch. Let the test cure 48 hours on a piece of cardboard before committing. If the floor is old and no chip matches, grout the repair in the closest color and then apply a grout colorant/sealer over all the joints in the room — a $15 to $25 bottle unifies everything in an afternoon and doubles as a sealer.
Step-by-Step Grout Repair
1. Remove the failed grout
Rake out the damaged joints to at least half the tile depth — 1/8 inch minimum, ideally 3/16 to 1/4 inch. New grout needs that depth to key in; a skim coat over old grout delaminates within months. Work the carbide saw or oscillating tool down the center of the joint, then clean the joint edges. Keep the blade off the tile edges; glazed edges chip if you lever against them. On a shower wall this is dusty, tedious work — figure 15 to 20 minutes per 10 linear feet by hand, a third of that with the multi-tool.
2. Clean and prep
Vacuum the joints thoroughly, then wipe with a damp sponge. Cement grout bonds poorly to dust. Joints should be damp-not-wet when you grout — on hot dry days, misting the joints prevents the porous edges from sucking the water out of the grout before it cures (that flash-drying is exactly how crumbly grout happens).
3. Mix the grout right
Follow the bag ratio and err dry — the mix should be peanut-butter thick and hold a peak. Let it slake (rest) 5 to 10 minutes, then remix without adding water. Overwatered grout is weak grout; this single mistake causes most premature failures.
4. Pack the joints
Force grout into the joints diagonally with a rubber float held at 45 degrees, making several passes from different directions so the joint fills completely with no voids. Then hold the float nearly upright at 90 degrees and squeegee the excess off diagonally, never parallel to the joints (parallel strokes rake grout back out).
5. Sponge and tool
Wait 15 to 30 minutes until the grout firms up and hazes, then sponge in light diagonal strokes with a barely damp sponge, rinsing constantly in clean water. Two goals: flush the joints to a slight concave profile that matches the old joints, and clean the tile faces. Too much water at this stage washes out the pigment and gives you blotchy, weak joints. Buff off the remaining haze with a dry microfiber cloth after a couple hours.
6. Cure and seal
Keep the repair dry for 24 hours (72 hours before soaking in showers), then seal cement grout with a penetrating sealer after it has cured about 48 to 72 hours. Sealing is what keeps the fresh joints from staining darker than their neighbors.
When the Repair Should Be Caulk, Not Grout
This is the rule that saves you from repeating the job annually: any joint where two planes meet gets flexible sealant, not grout. Tub-to-tile, shower corners, floor-to-wall, countertop-to-backsplash, and where tile meets wood or another flooring. These joints move seasonally, and rigid cement cracks there every time. Rake out the cracked grout completely, clean and dry the joint, and run a color-matched caulk — the major grout brands sell caulk matched to their grout colors, so the fix is invisible. If your “grout keeps cracking in the shower corner,” this paragraph is your answer.
Repair Costs: DIY vs. Hiring It Out
| Job | DIY materials | Pro cost (typical US) |
|---|---|---|
| Spot repair, a few joints | $10–$20 | $150–$300 minimum call |
| Regrout shower surround | $30–$60 | $400–$900 |
| Regrout 100 sq ft floor | $40–$80 | $500–$1,200 |
| Caulk change-of-plane joints | $10–$20 | $100–$250 |
Pros earn their money on removal speed and color blending, but a patient homeowner gets equal quality on small repairs.
Pre-Mixed Repair Grout vs. Powder
For repairs under a few square feet, the pre-mixed acrylic tubs deserve a serious look even though pros rib them. The color is factory-consistent (no mixing-water variables), a tub keeps for months once opened, and the acrylic tolerates slightly more joint movement than site-mixed cement. The trade-offs: cure-to-water time stretches to 3 to 7 days, it should not go in joints wider than about 3/8 inch or in constantly submerged spots, and per pound it costs three times the powder. My rule: pre-mixed for small floor and backsplash patches, powder for anything in a shower or bigger than a doormat.
Small Tricks That Make Repairs Invisible
- Feather your sponge strokes onto the surrounding old grout so there is no hard line between new and old.
- Grout an entire joint from tile corner to tile corner, even if only the middle cracked — partial-joint patches always show a seam.
- On floors, do the repair last thing in the evening so it cures overnight without foot traffic.
- Save a cup of dry grout from the batch, labeled, taped inside a vanity. Future you will be grateful.
Grout repair rewards patience at three moments: raking deep enough, mixing dry enough, and sponging gently enough. Get those right, put caulk where movement lives, seal when cured, and the repair outlasts the original. And if tiles sound hollow or a crack telegraphs through tile after tile, stop — fix the substrate problem first, because no bag of grout can hold down a floor that is moving underneath it.
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