Scrub grout with a paste of baking soda and water and a stiff nylon brush, then rinse. For stubborn stains, use an oxygen-bleach cleaner mixed as the label says and let it sit before scrubbing. Rinse well, dry the area, and seal cement grout once it's clean so it stays that way.
Grout is the part of a tiled floor or shower that makes the whole room look dirty — or clean. Because cement grout is porous, it soaks up soap, grease, body oils and dirty mop water, and slowly goes from white or light grey to dark. The good news: most dark grout is just dirty, not ruined.
Why grout gets dirty
- It's porous. Unsealed cement grout absorbs whatever sits on it.
- It sits lower than the tile. Mops and cloths glide over the tile and skip the grout lines.
- Dirty mop water. Mopping with the same water for the whole floor pushes grime into the lines.
- Moisture. In showers, grout that never dries can grow mildew — the black or pink spots.
How to clean grout, step by step
- Sweep or vacuum so you're not scrubbing grit into the lines.
- Make a paste of baking soda and a little water.
- Apply it along the grout lines with your finger (gloved) or an old toothbrush.
- Spray lightly with water, or with a mild dish-soap solution, and let it sit 5–10 minutes.
- Scrub with a stiff nylon brush. A grout brush or an old toothbrush works. Short back-and-forth strokes along the line.
- Rinse with clean water and wipe up the dirty residue straight away — don't let it dry back into the grout.
- Dry the area with a towel or a fan.
Some guides suggest spraying vinegar over the baking soda for fizz. On glazed ceramic or porcelain tile it's fine occasionally, but vinegar can etch natural stone and, over time, wear down cement grout. Plain water or dish soap is the safer default.
For tough stains and mildew
- Oxygen bleach (sodium percarbonate, sold as a powder) is the go-to for grey or stained grout. Mix it with warm water following the label, apply it to the grout, let it sit for the time the label gives, then scrub and rinse. It's colour-safe for most grout and doesn't have chlorine fumes.
- A steam cleaner with a narrow nozzle works well on floor tile grout — just not near wood floors or on unsealed stone.
- Mildew spots in the shower: a bathroom cleaner labelled for mildew, used as directed with the fan on. If the spots come back in the same place quickly, the moisture problem is the real issue. See our guide to condensation and mould.
Let us do the scrubbingA Good Maid deep clean gives bathrooms and floors the detailed attention regular cleans skip.
See my deep clean price →What not to use on grout
- Never mix chlorine bleach with vinegar, ammonia or other cleaners. The fumes are toxic.
- Wire brushes or metal tools — they scrape grout out of the joints and scratch tile.
- Acidic cleaners on natural stone like marble, travertine and limestone.
- Coloured cleaners or dyes on light grout unless you mean to change the colour.
Sealing grout, and when to replace it
Once cement grout is clean and completely dry (usually at least a day), a penetrating grout sealer helps it resist stains and water. Follow the product's directions; many need reapplying every year or two. A quick test: drip water on a grout line. If it darkens and soaks in within a few minutes, it's time to reseal.
Epoxy grout, common in newer showers, doesn't need sealing and resists stains much better.
Replace or repair grout when it's cracked, crumbling, missing, or has black mould that comes back from underneath. That's a tile-repair job rather than a cleaning one.
Keep grout clean between deep cleans with a squeegee after showers and fresh mop water for each room. Our bathroom cleaning checklist puts it all in order.
Frequently asked questions
What is the best homemade grout cleaner?
A paste of baking soda and water, scrubbed in with a stiff nylon brush and rinsed off, handles most dirty grout. For stubborn stains, an oxygen-bleach powder mixed as the label says works well.
Can I use vinegar on grout?
Occasionally on glazed ceramic or porcelain tile it's fine, but vinegar can etch natural stone and wear down cement grout over time. Plain water, dish soap or oxygen bleach are safer choices.
Why does my grout keep turning black?
Usually because it's unsealed and absorbing dirt, or because it stays damp and grows mildew. Clean it, let it dry fully, seal it, and improve ventilation in showers.
How often should grout be sealed?
Many sealers need reapplying every year or two. If a drop of water soaks in and darkens the grout within a few minutes, it's time.
Do house cleaners clean grout?
Our cleaners scrub showers, tubs and floors in every clean. Detailed grout scrubbing is part of a deep clean. Grout that's cracked or has mould underneath needs a tile repair specialist.
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