Grout is basically a line of porous concrete sitting a hair below the tile faces, which makes it a dirt trap by design. Every mop pass pushes dirty water into the lines, the water evaporates, and the grime stays behind. The good news: in most kitchens and bathrooms the grout itself is fine. It's wearing a film of soap scum, mineral scale, and tracked-in dirt — the same kind of buildup covered in our guide to removing hard water stains — and it comes off in layers. Work the ladder below from mild to strong, and stop at the first rung that does the job.
Dry-clean first. Vacuum or sweep the grout lines before anything gets wet. Loose grit under a scrub brush works like sandpaper, and you'll grind the very surface you're trying to save.
Hot water and a brush. Wet a test section with plain hot water and scrub. On sealed or lightly soiled grout this is honestly all it takes — and the test patch tells you how bad the rest of the room really is before you mix anything.
Baking soda paste. Stir baking soda with just enough water to make a paste about the thickness of toothpaste — roughly three parts soda to one part water. Spread it along the lines, scrub, and rinse with clean water. The mild abrasion plus mild alkalinity handles most kitchen floors.
Oxygen bleach soak, for whole floors. Dissolve oxygen bleach in hot water at the ratio on the label, mop or pour it on so every line stays wet, and give it 10–15 minutes before scrubbing the worst lines. This is the room-at-once method instead of line-by-line work. Rinse twice — cleaner residue left in grout grabs fresh dirt fast.
Peroxide for mildew spots. In showers, spray plain 3% hydrogen peroxide on the dark spots, wait about 10 minutes, scrub, and rinse. Test a hidden line first if your grout is colored. If the black stuff turns out to be growing on the caulk bead rather than the grout, that's a different fix — see our walkthrough on getting mold off shower caulk.
Steam, if you own a steam cleaner. Slow going, but heat and pressure lift grime out of the lines with no chemicals at all, which makes it the safest option around natural stone tile. Work short sections and wipe up the loosened sludge as you go, or it resettles.
Here's the test. Compare a grout line out in the open with one that's been hiding under a bath mat or behind the toilet, out of the traffic path. If the hidden line is the color you remember and the exposed lines still dry dark or blotchy after a full ladder clean, the discoloration has soaked into the grout's pores. Scrubbing can't reach it, because there is nothing left sitting on the surface to scrub off.
The honest fix at that point is a grout colorant — sold as grout refresh or grout paint — which recolors the line and seals it in the same pass. It goes on with a small brush, takes an afternoon for a bathroom, and looks startlingly like new grout. If the grout is also cracked, crumbling, or hollow-sounding under a tap, cleaning and coloring are both beside the point: that's a removal-and-regrout job, and our shower regrouting guide shows how the removal half of that work goes.
Clean cement grout drinks water. That's how it got dirty, and unsealed, it will happily do it again. A penetrating sealer, applied after the grout is completely dry — give it at least 24–48 hours after a deep clean — slows the next round way down. Most sealers call for a fresh coat every year or two; the label on yours is the authority. Epoxy grout is the exception: it doesn't need sealer, and if your grout shrugs off coffee and red wine no matter what you spill, that's probably what you have.
Grabbing a wire brush. It cleans fast by chewing the grout line wider and rougher, and a rougher line collects dirt faster next time. Nylon only, even if it means a second pass.
Sealing dirty grout. Sealer over grime locks the stain in and makes the colorant route harder later. The order is clean, dry, seal — never seal first and hope.
The one-bucket mop shortcut. Mopping with a single bucket of grey water mostly redistributes the dirt into the lines and calls it cleaning. Grout needs a brush and rinse water that's actually clean.
Reaching for chlorine bleach first. It's the harshest option on the ladder, the riskiest bottle in the cabinet, and it fades colored grout. The ladder exists so you rarely get there.
Brush, paste, soak, seal. Most grout that looks ruined is two rungs up the ladder and a coat of sealer away from looking new again, and the whole job on a typical bathroom floor costs a few dollars in supplies you probably already own. Save the colorant for grout that's stained through and regrouting for grout that's falling out. Everything else is just cleaning, and cleaning is cheap.
Kitchen and bathroom floors hold up well with a full ladder clean a few times a year, plus fresh sealer every year or two. Shower grout in daily use benefits from a quicker scrub every month or so, before mildew gets a foothold in the corners.
It can fizz away mineral film on ceramic or porcelain tile, but it's hard on cement grout with repeated use — acid slowly dissolves the surface — and it etches natural stone outright. A baking soda paste gets most people the same result without either risk.
Yes. The heat loosens the grime film and the jet lifts it out of the line, no chemicals involved. It's slow on a big floor, but it's the safest method around stone tile and the best option for anyone avoiding cleaner fumes in a small bathroom.
Water temporarily darkens even clean grout, so judge the result dry. If it dries back to blotchy and dark in the traffic lanes while the edges of the room stay light, the stain is down in the pores. That's the colorant situation, not a scrubbing failure.
Yes, if it's cement grout — once it has dried fully, at least a day or two after a wet deep clean. Sealer doesn't make grout waterproof or stain-proof; it slows absorption down enough that spills wipe up instead of soaking in. That bought time is the whole point.