Quick answer: Clean the surrounding tiles first, then spray the grout with white vinegar or make a bicarbonate of soda paste and leave it for five to fifteen minutes. Scrub with a soft grout brush or old toothbrush, then rinse thoroughly with clean water and dry with a towel. Never use vinegar on natural stone tiles, since it can etch and permanently dull the surface.
Grout does an unglamorous but essential job holding tiles together and keeping water out, and its porous nature means it soaks up dirt, soap, and moisture rather than letting it sit on the surface like glazed tile does. That’s exactly why grout discolours faster than the tiles around it, and why a proper clean makes such a visible difference to a whole room.
Why Grout Gets Dirty So Quickly
Grout is porous, unlike the glazed tiles it sits between. Water, oil, and soap residue soak into it rather than wiping off, which is why dirt becomes trapped inside the material over time rather than simply sitting on top. In bathrooms particularly, warm damp air with nowhere to go creates exactly the conditions mould spores need, and this moisture soaks straight into the grout lines.
Before You Start: Clean the Tiles First
It might seem backwards to clean before you clean, but wiping down the surrounding tile surfaces with an all-purpose cleaner first stops loose dirt falling into freshly cleaned grout and undoing your work. This matters even more with lighter grout colours, which show new staining quickly.
What You Will Need
- White vinegar (avoid on natural stone)
- Bicarbonate of soda
- Hydrogen peroxide (3% solution), optional for black mould
- A soft grout brush or old toothbrush
- A microfibre cloth
- Rubber gloves and eye protection
Method 1: White Vinegar
- Spray white vinegar directly onto the grout lines.
- Leave it to sit for around five minutes, letting the acidity break down mineral deposits and mild mould.
- Scrub with a soft grout brush, working along the lines rather than across them.
- Rinse thoroughly with clean water and dry with a towel or microfibre cloth.
Never use vinegar on natural stone tile such as marble, limestone, or travertine, since the acid can etch and permanently dull the surface. Also avoid it on sealed grout or polished finishes, where it can degrade the sealant.
Method 2: Bicarbonate of Soda Paste
- Mix bicarbonate of soda with a small amount of water to form a thick paste.
- Apply it directly to the grout lines, working horizontal lines first, then vertical.
- Leave it to work for ten to fifteen minutes.
- Scrub with a grout brush, then rinse thoroughly with clean water.
Method 3: Hydrogen Peroxide (For Black Mould)
Hydrogen peroxide, the standard 3% solution available from any chemist, is particularly effective on black mould spots.
- Spray hydrogen peroxide directly onto the mouldy grout.
- Leave it to sit for a few minutes, allowing it time to break down the mould.
- Scrub with a brush, then rinse thoroughly.
- Repeat if the stain is stubborn, since heavier mould sometimes needs a second application.
For particularly tough combined staining, mix bicarbonate of soda with hydrogen peroxide instead of water to make a stronger paste, apply it the same way, then scrub and rinse.
Method 4: Steam Cleaning
A steam cleaner can lift ingrained dirt from grout lines using heat alone, without any chemicals.
- Fill the steam cleaner with water only, following the manufacturer’s instructions.
- Once heated, apply the cleaning brush attachment directly to the grout lines.
- Go over stubborn areas a few times, then dry the area thoroughly with a cloth.
Be aware that steam cleaning can strip away grout sealant along with the dirt, so you may need to reseal afterwards.
Preventing Grout From Getting Dirty Again
- Spray the shower with a 1:1 vinegar and water solution before stepping out, which helps stop soap scum and mineral deposits settling into the grout.
- Keep the bathroom well ventilated with an extractor fan or an open window, since good airflow significantly reduces mould returning.
- Wipe down tiles and grout regularly rather than waiting for visible staining to build up.
- Reseal grout every twelve to eighteen months to help it resist future staining and moisture.
When Cleaning Isn’t Enough
If you’ve tried every method above with plenty of elbow grease and the grout still looks tired, a grout reviver pen can restore a bright, uniform colour to discoloured lines without needing to regrout. For grout that is cracked, crumbling, or has been beyond saving for some time, regrouting is a relatively low-cost option that gives a genuinely fresh result rather than repeatedly fighting the same stains.
Related Guides
Frequently Asked Questions
Why does grout turn black or mouldy?
Grout is porous and absorbs moisture and soap residue rather than letting it sit on the surface. In bathrooms without good ventilation, warm damp air soaks into the grout and creates ideal conditions for mould to develop.
Is vinegar safe to use on all grout?
No. Vinegar is safe on standard grout between ceramic or glazed tiles but should never be used on natural stone tiles like marble or limestone, since the acid can etch and permanently damage the surface.
How often should grout be resealed?
Every twelve to eighteen months for most bathrooms, which helps it resist staining and moisture between deep cleans.
Is it cheaper to clean grout or replace it?
Cleaning is almost always cheaper and worth trying first. Regrouting is a relatively low-cost option worth considering only once grout is cracked, crumbling, or genuinely beyond restoring through cleaning.
Final Thoughts
Grout looks worse than it needs to mainly because of its porous nature, but vinegar, bicarbonate of soda, or hydrogen peroxide will restore most everyday staining with a bit of scrubbing. Keep ventilation good and give tiles a regular wipe-down, and grout will need far less deep cleaning over time.