Short answer
Clean grout by working along the lines themselves with a stiff, narrow brush and a mild cleaner, starting with warm water and washing-up liquid or a bicarbonate of soda paste, then rinsing and drying. Only move up to a stronger grout or tile cleaner if the gentle method fails, test it on a hidden spot first, and never mix products. Grout that is cracked or crumbling needs regrouting rather than cleaning.
Why grout gets dirty when tiles stay clean
Most grout is cement-based and porous, so it soaks up water, soap residue and cooking grease that simply wipe off a glazed tile. On floors the grout lines sit a little lower than the tiles, so dirty mop water settles into them every time the floor is washed. In showers, the lines stay damp for long periods, which is why black mould tends to appear there first.
Wiping across tiles with a cloth or mop cleans the tile faces but tends to push grime further into the grout. The trick is to clean the line, not the surface around it.
Check your tiles before you choose a cleaner
Glazed ceramic and porcelain tiles are tough and tolerate most household cleaners. Natural stone, such as marble, limestone and travertine, is different: acidic products like vinegar, lemon or some descalers can etch the surface and leave dull marks that cannot be wiped away. If you are not sure what your tiles are made of, treat them as stone and use pH-neutral products only.
Coloured grout can also fade or blotch with bleach-based cleaners. Whatever you plan to use, test it on a small, out-of-sight area first and let it dry before judging the result.
What you will need
A stiff, narrow grout brush or an old toothbrush, warm water, washing-up liquid, bicarbonate of soda, clean cloths and rubber gloves. Avoid wire brushes and metal scrapers, which gouge grout and scratch glaze. With a shop-bought cleaner, add eye protection and open a window.
Step by step
- Clear the area and vacuum or sweep floor tiles so loose grit does not scratch the surface as you scrub.
- Start gently. Wet the grout with warm water and a little washing-up liquid and scrub along each line with the brush, working in small sections.
- For lines that stay grey, mix bicarbonate of soda with a little water into a paste, press it into the grout with the brush or a finger in a glove, leave it to sit briefly, then scrub again.
- Rinse the section with clean water and a cloth, changing the water as soon as it looks dirty, so you are not wiping grime back into the lines.
- If marks remain, try a grout or tile cleaner suitable for your tile type. Follow the label for dilution and contact time, keep the room ventilated and rinse it off completely.
- Dry the tiles and grout with a clean towel. On floors, keep people off until everything is fully dry.
Black mould in shower grout
Spots of black mould in shower grout can often be lifted with a mould remover made for bathrooms. Use it exactly as directed, ventilate well, wear gloves and keep it away from natural stone unless the label says it is suitable. Never use a mould remover or bleach alongside any other cleaner, especially anything acidic or ammonia-based, as some combinations give off harmful gases.
If mould keeps coming back in the same place, look at how the room dries out. Running the extractor fan during and after showers, leaving the door open and wiping down the screen and tiles after use all reduce the damp that mould needs.
Silicone sealant around the bath, shower tray and basin is not grout. When black mould has grown into the silicone itself, cleaning rarely gets it out, and the usual fix is to cut the old sealant out and apply new.
Keeping grout cleaner for longer
Once cement grout is clean and completely dry, a penetrating grout sealer can help it resist stains, as long as it suits your tiles; follow the product instructions and test it first. After that, a quick wipe-down of shower walls, mopping floors with clean water that is changed often, and dealing with splashes behind the hob promptly will keep the lines from darkening as quickly. Our guide to cleaning hard floors covers mopping methods for tiled floors in more detail.
Clean or regrout?
Cleaning lifts dirt and residue sitting on or near the surface of the grout. If the grout is stained right through, it may lighten without returning to its original colour. If it is cracked, crumbling, missing in places or lets water through, it has failed. That is a repair job: the old grout is raked out and new grout is applied.
When to call a professional
It is worth calling a professional when a whole floor or bathroom needs doing and the gentle method is barely making a difference, when you have natural stone and do not want to risk the wrong product, or when you would like the room brought back up to standard before a sale, a new tenancy or a family occasion.
We clean wall and floor tiles and grout in kitchens and bathrooms across Essex, as well as washrooms and staff kitchens in commercial premises. We will tell you honestly what we see before the work starts, including whether grout or silicone is past cleaning and needs replacing instead. Call Jason on 07774 252535 or ask for a free quote.
Rather have it done for you?
Kitchen and bathroom tiles and grout lines cleaned of soap residue, grease and grime. Family-run by Jason and Lucas Prior, covering south Essex.
Frequently asked questions
What is the best homemade grout cleaner?
Warm water with a little washing-up liquid, or a paste of bicarbonate of soda and water, scrubbed along the lines with a stiff narrow brush. Avoid vinegar on natural stone, and never mix homemade mixtures with bleach or other cleaners.
Can I use bleach on grout?
Only on ceramic or porcelain tiles with white grout, diluted as the label says, in a well-ventilated room and never mixed with any other product. Bleach can fade coloured grout and is not suitable for many stone tiles.
Why does my grout go black again so quickly?
Usually because the area stays damp, or because the grout is porous and unsealed. Better ventilation, drying the shower after use and sealing clean, dry grout all help.
Should I seal grout after cleaning?
Sealing clean, completely dry cement grout with a suitable penetrating sealer can help it resist stains. Check that the product suits your tiles and test it on a small area first.
Related guides
- How to clean hard floors: routine and deeper cleaning for vinyl, LVT, tiled and natural stone floors, with the products each one needs and the ones to avoid.