How to Repair Cracked or Damaged Grout Between Tiles

Grout fails because it's porous and sits in the one place where water, temperature swings, and movement converge. Cracks let water behind the tile, and water is your enemy—it turns into mold, loosens adhesive, and eventually rots substrate. The good news is that regrout repair is straightforward and doesn't require a professional. You're just clearing out the old, dead material and replacing it with fresh grout that will harden and seal the joint again. This repair works on shower walls, bathroom floors, kitchen backsplashes, and any tiled surface where grout has failed. The scope matters. A single cracked line running through grout joints calls for targeted removal and regrout. Wide cracks, spalling, or grout that crumbles when you touch it means full joint removal and replacement. Either way, you'll spend a weekend on this, and the result is a watertight, lasting repair.

1. Read the Grout First. Examine the crack or damage closely. Tap the grout with a screwdriver handle—if it crumbles or sounds hollow, it needs full removal down to the substrate. If it's a hairline crack in otherwise solid grout, you may only need to apply grout caulk. For repairs wider than 1/8 inch or any spalling, plan on removing grout to a depth of at least 1/4 inch, ideally up to half the joint width.
2. Excavate the Dead Grout. Use a manual grout saw for isolated repairs—place the blade in the joint, angle it slightly, and saw back and forth with steady pressure. For larger areas, a rotary tool with a grout-removal bit is faster and more uniform. Work the entire length of the damaged joint, keeping the blade centered in the grout line. Remove grout to a consistent depth—aim for at least 1/4 inch. Blow out dust as you go with compressed air or a shop vac.
3. Clear the Battlefield. Vacuum out all loose grout dust and debris using a shop vac with a hose attachment. Follow with a damp cloth or sponge to wipe the joint clean—you want bare tile edges and substrate visible. Let the joint dry completely before you grout. For bathroom joints, wait at least 2 hours or overnight if the air is humid. If the area behind the grout is still damp or shows mold, spray with a mold-killing cleaner, let it sit 10 minutes, then rinse and allow to dry.
4. Mix to Peanut Butter. Pour unsanded or sanded grout (depending on joint width—use sanded for joints wider than 1/8 inch) into a bucket with clean water. Stir with a drill-mounted paddle or by hand until you reach a peanut-butter consistency. The mix should hold together when squeezed but still be workable. Let it sit for 5 minutes (called slaking), then stir again briefly. Don't add extra water if it thickens; work with what you have.
5. Force Grout Home. Hold a grout float (the trowel with rubber face) at a 45-degree angle to the tile surface. Load grout onto the float and force it into the joint using firm, diagonal strokes. Go in both directions along the joint length so you're packing grout from above and beside. Don't worry about smoothness yet—your goal is to fill the void completely with no voids or air pockets. Overfill slightly so grout sits proud of the tile surface.
6. Strike the Joint. Wait 15–20 minutes for the grout to firm up slightly, then use the grout float held at a 90-degree angle to rake off excess. Draw the float diagonally across the joints, not parallel to them, to avoid pulling grout back out. The finished joint should be slightly concave and flush with the tile face. If you overstrike and pull grout out, let it firm up more and try again. Stop when the joint looks consistent with adjacent grout lines.
7. Wait, Don't Shower. Once grout firms up (30–45 minutes), use a damp sponge in circular motions to wipe tile faces clean. Rinse the sponge between passes. Do not overwork the joints—gentle passes only. After cleanup, don't let water run on the repair for at least 24 hours. Keep the area dry and undisturbed. Grout cure time varies by type; standard grout takes 48–72 hours before it can handle moisture. Epoxy grout cures faster—check the bag.
8. Seal It In. Once grout is fully cured, apply a penetrating grout sealer according to product instructions—this is most important in bathrooms and kitchens where grout contacts water regularly. Pour a small amount of sealer onto the joints and work it in with an applicator bottle or brush. Seal both sides of a joint if exposed. Let it cure per product directions (typically 24–48 hours) before allowing water contact.