Tile Grout Repair: Removal, Replacement, and Resealing
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Grout deteriorates before the tile does. Cracks, stains, and crumbling joints are cosmetic problems that become water damage if you ignore them. The repair is hands-and-knees work but not difficult. Removing the old grout is the slow part. Applying new grout goes quickly once the joints are clean, and the result looks like a brand new tile installation.
When to Repair vs. Replace All Grout
Repair individual joints when you see isolated cracks, chips, or missing sections. This is spot work: remove the damaged grout from specific joints and refill them. Spot repairs take 30 minutes to an hour for a small area and the material cost is minimal.
Replace all the grout when the damage is widespread, the color has become permanently stained, or the grout is soft and crumbles when you scrape it with a utility knife. Full regrouting gives you a uniform appearance and fresh sealant protection across the entire surface. A typical bathroom floor (about 40 to 60 square feet) takes 3 to 5 hours for complete grout removal and replacement.
If tiles are loose or hollow-sounding (tap them with your knuckle or a small rubber mallet), the problem is underneath the grout. A bonded tile sounds solid. A loose one sounds hollow. Loose tiles need to be pulled up, the old thinset adhesive cleaned off both the tile and the substrate, and the tile reset with fresh thinset before regrouting. Regrouting over a loose tile just hides the problem temporarily, and the grout will crack again as the tile continues to move.
Grout Removal Tools
A manual grout saw (a small blade with carbide grit, about $5 to $8) removes grout from individual joints. It is slow but gives you the most control and is the safest option for tile edges. For spot repairs on a few joints, a manual saw is all you need. Manufacturers like Kraft Tool and QEP make durable options available at most hardware stores.
For larger areas, an oscillating multi-tool with a grout removal blade speeds up the work significantly. The Fein MultiMaster, DeWalt DCS354, and Milwaukee M18 oscillating tools all accept grout removal blades. Set the depth stop so the blade does not go deeper than the grout joint. You do not want to chip the tile edges or disturb the thinset underneath. A grout removal blade for an oscillating tool runs $8 to $15 and handles dozens of linear feet before wearing out.
A rotary tool (Dremel-style) with a grout removal bit works well for narrow joints. The Dremel 570 wall tile cutting bit and the dedicated grout removal attachment are the most common options, running about $10 to $20. Rotary tools are faster than a manual saw but require a steady hand to avoid chipping glaze on the tile edges.
Whichever tool you use, remove grout to at least 2/3 of the joint depth. Shallow removal gives the new grout insufficient thickness and it will crack out again within months. Vacuum the dust from the joints after removal. A shop vac with a crevice attachment gets into the narrow joints effectively.
Choosing New Grout
Sanded grout fills joints wider than 1/8 inch. Unsanded grout fills joints 1/8 inch and narrower. Using sanded grout in narrow joints is difficult because the sand particles are too large to work into the space. Using unsanded grout in wide joints causes shrinkage cracking as the material cures. Match the grout type to your joint width. Most floor tile uses sanded grout. Most wall tile with tight joints uses unsanded.
Color matching matters if you are doing spot repairs rather than full replacement. Grout color changes as it cures: wet grout is noticeably darker than dry grout. Buy a small amount and test it in an inconspicuous spot, letting it dry fully (at least 72 hours) before comparing to the existing grout. Manufacturers like Mapei, Prism, and Custom Building Products offer color-matching charts on their websites and in-store displays. Bring a piece of the old grout to the store if possible.
If exact color matching is not possible (the existing grout has faded or yellowed with age), regrouting the entire surface with a new color is sometimes the better approach. It takes more time but produces a clean, uniform result.
Epoxy grout is stain-resistant, waterproof, and does not need sealing. It is the premium option for showers, kitchen countertops, and other areas with heavy moisture exposure. However, it is harder to work with (shorter working time, stickier consistency) and more expensive (about $30 to $50 per unit vs. $8 to $15 for standard grout). User reviews consistently note the difficulty of cleanup if you let it haze on the tile surface.
Applying New Grout
Dampen the joints lightly with a sponge before grouting. Dry joints pull moisture out of the grout too fast and weaken the cure. The joints should be damp, not wet. Standing water in the joints dilutes the grout.
Mix grout to the consistency of thick peanut butter, following the manufacturer's water ratio on the bag. Too much water is the most common mixing mistake and results in weak, discolored grout. Let the mix sit (slake) for 10 minutes after initial mixing, then stir briefly again before use. This rest period allows the polymers and cement to fully hydrate.
Work the grout into the joints at a 45-degree angle with a rubber grout float, pressing firmly to fill the joint completely. Pull the float diagonally across the tile to remove excess without pulling grout out of the joint. If you drag the float parallel to a joint, the edge of the float dips into the joint and scoops grout out.
Let the grout set for 15 to 30 minutes (it will haze on the tile surface), then wipe diagonally with a damp sponge. Rinse the sponge frequently and wring it nearly dry. Too much water washes pigment out of the grout and weakens it. A second pass with a barely damp sponge removes remaining haze. Buff with a dry cloth after another 30 minutes. Keep the grout damp for 72 hours during curing by misting it lightly if the air is dry.
Sealing Grout
Seal grout with a penetrating grout sealer after it has fully cured. Most manufacturers specify at least 72 hours before sealing, and 28 days for maximum durability. Penetrating sealers absorb into the grout and block moisture and stains without changing the appearance. Topical sealers form a film on the surface that can peel and discolor over time. For most residential applications, a penetrating sealer is the better choice.
Apply sealer with a small brush, a foam roller, or a squeeze-bottle applicator that targets just the grout lines. Products like the Miracle Sealants 511 Impregnator (about $15 to $25) are widely recommended for residential use. Wipe excess sealer off the tile surface immediately. Sealer on glazed tile creates a hazy film that is difficult to remove once it dries.
In wet areas (showers, tub surrounds, kitchen backsplashes), reseal annually. In dry areas (floor tile in living spaces), every 2 to 3 years is sufficient. You can test whether the existing sealer is still effective by dropping a few drops of water on the grout. If the water beads up, the sealer is working. If it absorbs into the grout and darkens it, the sealer has worn off and needs reapplication.
Frequently Asked Questions
Can I Apply New Grout Over Old Grout?
Not effectively. New grout does not bond well to old grout surfaces, and the resulting joint is too thin to be durable. It will crack and fall out quickly. You must remove the old grout to at least 2/3 of the joint depth before applying new grout. This gives the new material enough thickness to cure properly and bond to the sides of the tiles rather than sitting on top of the old grout.
How Do I Remove Grout Stains Without Replacing the Grout?
For surface stains, a grout cleaning solution (hydrogen peroxide-based for organic stains, oxygen bleach for mildew) and a stiff nylon brush often restore the color. Products like OxiClean Versatile Stain Remover or ZEP Grout Cleaner work well for most household stains. For deep stains that do not respond to cleaning, a grout colorant or grout pen covers the existing grout with a new color layer. It is faster than regrouting and works well when the grout is structurally sound but permanently discolored.
Why Does My New Grout Keep Cracking?
The three most common causes are: grout mixed too wet (excess water weakens the cure and increases shrinkage), joints not cleaned deep enough (thin grout cracks as it shrinks because there is not enough material), and substrate flex (the surface underneath moves when walked on). Fix the first two by mixing stiffer grout and removing old grout deeper. Fix the third by addressing the structural issue, typically adding screws to tighten the subfloor to the joists, or installing cement board as an underlayment to create a rigid surface.