How to Clean Grout: What Works, What Ruins It, and When to Call a Pro

You mop the kitchen every week, the tile looks clean — and the grout lines keep getting darker. We hear this all the time, and it isn't your fault. Grout is porous, and mopping is often what makes it dirty.

This guide explains how to clean grout the right way: the safe DIY methods that work, the popular "hacks" that slowly destroy grout and stone, and the signs that it's time for a professional deep clean. It's written for real New York homes — prewar bathrooms full of tiny hex tile, busy family kitchens, and Long Island entryways that take a beating from sand and road salt.

Why grout turns dark

Most grout is made of cement, sand and water. Once it hardens, it's full of tiny pores — like a hard sponge. Tile is smooth, so dirt slides off it. Grout sits a little lower than the tile, so dirty water runs into the lines and soaks in.

That's the mop problem. After the first few strokes, your mop water is dirty. Every pass spreads that water across the floor, it drains into the grout lines, and when it dries, the dirt stays behind. Do that every week for a few years and light gray grout turns brown or almost black.

In bathrooms there's a second problem: soap scum, body oils and moisture. Shower grout stays damp, and that's exactly what mildew likes. The pink or black spots in the corners of a shower are usually mildew growing on soap residue in the grout.

First, know what you're cleaning

Before you grab any cleaner, take ten seconds to check two things. The wrong product on the wrong surface can cause damage you can't undo.

Is the tile ceramic, porcelain or natural stone?

Ceramic and porcelain are tough and handle most cleaners. Natural stone — marble, limestone, travertine and slate — is different. Marble and other calcium-based stones react with acid. Even a splash of vinegar or lemon can leave dull, etched marks on polished marble. Many NYC bathrooms have marble floors, marble thresholds (saddles) at the doorway, or marble shower walls, so check before you clean.

Is the grout cement-based or epoxy?

Almost all older grout is cement-based and porous. Epoxy grout, used in some newer kitchens and showers, is slightly shiny, feels like plastic, and resists stains much better. If your grout looks glossy and has never really darkened, it's probably epoxy and only needs gentle cleaning.

Grout cleaners: what's safe and what isn't

How to clean grout yourself: step by step

1. Remove loose dirt first

Vacuum or sweep the floor well, paying attention to the grout lines. Sand and grit act like sandpaper when you scrub, and they turn into mud the moment they get wet.

2. Pre-wet and apply your cleaner

Work in small sections, about three feet by three feet. Wet the grout with warm water and a little pH-neutral cleaner. For darker lines on ceramic or porcelain, spread a paste of baking soda and water along the grout. For mildew or stubborn stains, spray 3% hydrogen peroxide, or mix oxygen bleach powder with warm water following the label. Let it sit for five to ten minutes. Don't let it dry.

3. Scrub with the right brush

Use a stiff nylon grout brush or an old toothbrush. Scrub along the line, then across it. Never use a wire brush or steel wool — they scratch tile, gouge grout, and steel wool can leave rust marks.

4. Pick up the dirty water — this is the step most people skip

Scrubbing loosens the dirt, but if you leave that dirty water on the floor, it soaks right back into the grout. Wipe it up with clean microfiber towels, a squeegee, or a wet-dry vacuum. Then rinse the section with clean water and pick that up too.

5. Dry it and keep air moving

Run a fan or open a window. In bathrooms, turn on the exhaust fan and leave the shower door open. Grout that dries fast stays cleaner and grows less mildew.

Mistakes that ruin grout

• Using vinegar every week. It's popular online, but regular acid cleaning slowly washes away the cement in the grout. Lines get sandy, rough and wider — and dirtier.
• Mixing cleaners. Bleach plus vinegar, ammonia or many bathroom cleaners creates toxic gas. Use one product, rinse, then use another if you must.
• Mopping with a dirty mop. Change the water often, or use a flat microfiber mop with clean pads. A dirty string mop is a grout-darkening machine.
• Sealing dirty grout. Sealer locks in whatever is in the pores. Always deep clean first and let the grout dry fully.
• Steaming cracked or loose grout. Heat and pressure can push water under damaged grout and loosen tiles. Repair first.

When DIY isn't enough

If you've scrubbed and the lines are still dark, the dirt is deep in the pores where a brush can't reach. That's when professional tile and grout cleaning makes a real difference. Here's how our IICRC-certified technicians do it:

1. Inspect and test. We identify the tile, stone and grout type, and check for cracked or missing grout. If a stain is permanent, we tell you before we start.
2. Protect the room. Nearby carpet, rugs, cabinets and wood floors are covered.
3. Pre-treat. A cleaner matched to your surface goes on — stone-safe products for marble and travertine — to loosen soil and oils from the grout.
4. Agitate the lines with grout brushes, by machine and by hand in the corners.
5. High-pressure hot-water rinse with extraction. The dirty water is pulled up at the same moment it's rinsed, so nothing settles back into the grout.
6. Optional sealing. A penetrating sealer fills the pores so spills and mop water stay on top, and your weekly cleaning actually works again.

The floor is usually dry within a few hours. If you choose sealing, we'll tell you how long to keep foot traffic light while it cures. Many families book grout on the same visit as their carpet cleaning, so the whole home is done in one appointment.

NYC apartments: hex tile, marble and building rules

Many prewar apartments in Manhattan and brownstones from Park Slope to Harlem still have original small white hex or penny tile. These floors have far more grout per square foot than modern large tile, so they darken quickly and take forever to scrub by hand. They're often next to a marble saddle that acid cleaners will etch.

Co-ops and condos usually require a certificate of insurance before any contractor goes upstairs. We're licensed and insured and provide COIs for buildings — our COI guide for NYC buildings explains what to ask your managing agent so there's no delay at the front desk.

Long Island homes: sand, salt and mudrooms

In Nassau County and Suffolk, tile entryways, mudrooms and kitchens get beach sand all summer and road salt all winter. Salt leaves a white film on tile and a crust in the grout lines, and it gets tracked onto carpet too — see our guide to winter salt stains. A deep grout clean and fresh sealer in late fall, before the first snow, makes the whole winter easier.

If grout stays damp near a tub, a dishwasher or a basement wall, look for a hidden leak. Ongoing moisture can damage the subfloor, and that's a job for our water damage restoration team.

How to keep grout clean longer

• Daily or weekly: sweep or vacuum, then damp-mop with clean water and a pH-neutral cleaner.
• After every shower: squeegee the walls and run the fan for a while.
• Monthly: spot-scrub the grout in busy areas — in front of the sink, stove and doorways.
• Every one to two years: a professional deep clean and reseal for most kitchens and baths; more often for busy entryways and businesses.
• At the door: use good mats inside and outside to stop sand and salt before they reach the tile.

Frequently asked questions