How to Patch Cracked Tile Grout

Cracked grout lines look bad and invite water into spaces where it doesn't belong. Once water gets behind tile, rot and mold follow fast. The good news: patching cracked grout is one of the easiest tile repairs you can do, and you don't need special skills or expensive tools. If the cracks are small and isolated—not a grid of failures across your whole floor or wall—this is pure DIY territory. You'll have a waterproof seal again by tomorrow.

1. Identify Your Damage Level. Look at the cracks. If they're surface-level spider cracks in otherwise solid grout, use a grout colorant or epoxy pen. If the grout is actually missing or loose, you'll need to remove the old stuff and regrout. Press firmly along the cracked line with a screwdriver—if grout crumbles or falls out, it's time to remove and refill.
2. Carve Out the Damage. Use a grout saw (a small carbide tool that looks like a miniature hacksaw blade) or a rotary tool with a grout-removal bit to cut out the bad grout along the crack. Work slowly and keep the blade centered in the joint. You're aiming to remove about ¼ inch deep and create a clean, V-shaped channel. Don't gouge the tile itself.
3. Clear and Dampen the Channel. Use a shop vac to remove all dust and debris from the channel. Then dampen the joint with a wet sponge or cloth—not soaking wet, just damp. This prevents the porous grout from drying too fast and cracking again. Let excess water drain.
4. Mix the Perfect Batch. If using powdered grout, mix a small batch—just enough for your patch job—with water to a peanut butter consistency. Stir for 2 minutes, then let it sit for 5 minutes and stir again. If using pre-mixed grout or a grout pen, follow the manufacturer's directions. For color matching, bring a sample of old grout to the hardware store or test the new grout on an inconspicuous joint first.
5. Pack the Joint Tight. Using a grout float or a putty knife held at a 45-degree angle, push fresh grout firmly into the channel. Overfill slightly—grout will shrink. Work along the length of the crack in one direction, then repeat if needed to completely fill the gap. Press hard enough that you hear a slight resistance.
6. Strike It Flush and Smooth. Wait 15-20 minutes for the grout to firm up slightly, then use a wet sponge or a grout joint tool to smooth the surface flush with the surrounding grout lines. Work in light, diagonal strokes. The goal is a clean, level surface that matches the depth and shape of the adjacent joints. Don't oversaturate or you'll pull grout back out.
7. Wait, Then Seal. Allow the patched grout to cure for 24-48 hours before exposing it to water. Keep the area dry during this window. Once cured, you can apply grout sealer if you're in a wet area like a shower or outside the bathtub. Sealer prevents staining and extends the life of your patch.