Deep-Clean Grout Lines the Right Way

Grout collects dirt, mildew, and soap scum faster than almost any surface in your home, and once it darkens, it makes your entire tile installation look aged and neglected. The good news: deep-cleaning grout is straightforward, requires no harsh chemicals or expensive equipment, and the results are immediate. What separates a half-hearted attempt from real results is patience and the right abrasive—something textured enough to lift embedded grime without damaging the grout itself. This guide walks you through a method that works on bathroom tile, kitchen backsplashes, and shower surrounds without requiring a steam cleaner or a contractor's truck.

1. Clear the Space First. Remove any bottles, bath mats, or loose items from the tile surface. Use a dry cloth to wipe down the grout lines and surrounding tile to remove loose dust and debris. This prevents dirt from turning into mud when you apply your cleaning paste, which wastes effort and leaves a mess.
2. Mix Your Weapon. In a small bowl or container, combine three parts baking soda with one part hydrogen peroxide (3% household grade from any drugstore). Stir until you have a thick, spreadable paste, similar to toothpaste consistency. If it's too dry, add peroxide a teaspoon at a time. If it's too wet, add baking soda. The paste should cling to the grout without running.
3. Pack It Deep. Using an old toothbrush, a grout brush, or a small painting brush, work the paste directly into each grout line. Press it in rather than just coating the surface. Pay special attention to corners where tiles meet and anywhere you see visible discoloration. The paste should fill the joint completely.
4. Let Chemistry Work. For light discoloration, you can scrub immediately. For stubborn mold, mildew, or deep stains, let the paste sit in place for 10–15 minutes. The hydrogen peroxide does the chemical work of breaking down the stain while you wait—don't leave it longer than 15 minutes or it begins to dry out and become harder to scrub.
5. Scrub It Out. Using your grout brush or toothbrush, scrub along the length of each grout line with medium to firm pressure. Work in one direction rather than random circles—this helps lift the paste and dissolved grime out of the joint rather than pushing it around. Scrub for 30–60 seconds per line, longer for heavily stained areas. You'll see the paste darken as it lifts dirt.
6. Wipe It Clean. Use a damp (not soaking) cloth to wipe away all the baking soda paste from the grout lines and surrounding tile. Rinse your cloth frequently under running water and keep wiping until you see no residue. A second pass with a clean, damp cloth ensures you've removed all the paste, which can look chalky if left behind.
7. Assess the Results. Use a dry cloth or old towel to dry all the grout lines and tile. As the grout dries, you'll see the true color and how much stain remains. Dried grout should look noticeably lighter. If you still see discoloration after drying, repeat the paste-sit-scrub-rinse cycle on those areas.
8. Go Again if Needed. If any areas remain discolored after the first pass, mix a fresh batch and repeat steps 3–6 on those specific lines. Most grout responds to one or two passes. Very old mold or heavy mineral deposits may need three applications, spaced a day apart to avoid over-scrubbing.
9. Ventilate and Cure. Open windows and doors to ventilate the area for at least 30 minutes. The hydrogen peroxide smell dissipates quickly, but air circulation also helps the grout dry evenly. Avoid walking on wet tile or applying water to the area for at least an hour after cleaning.
10. Protect Your Work. Once the grout is completely dry (wait 24 hours), apply a penetrating grout sealer per the product instructions. Sealer doesn't prevent all staining, but it does slow how quickly dirt and mold reattach to the grout surface, making your next cleaning easier and extending the time between deep cleans to 6–12 months.