You can scrub a bathroom tile until it shines and still find that the narrow lines between the tiles look grey. Grout has a different surface from glazed tile. Cement-based grout is often porous and collects soap residue, dirt and moisture; epoxy and specialist grouts may behave differently. That is why a cleaner that works beautifully on glass may not be suitable for the joints.
Begin by identifying the grout and tile, removing ordinary surface dirt and using a mild method. Strong acids, bleach and abrasive tools can damage some materials, so don't make them your first move.
Work out what you're cleaning
Look closely at the joints. Grout fills the gaps between tiles, while flexible silicone sealant is normally used where surfaces meet, such as a shower corner or around a bath.
Silicone shouldn't be attacked with a stiff grout brush. If it is mouldy deep inside or peeling away, replacement may be necessary rather than repeated scrubbing.
Check whether the tiles are ceramic, porcelain or natural stone. Marble and limestone can react badly to acidic cleaners, even if the grout itself seems unaffected.
Check for damaged or missing grout
Before introducing water, inspect for cracks, crumbling joints or loose tiles. Water entering behind failed grout may contribute to a much larger damp problem.
Cleaning won't restore a joint that has lost material. If gaps are significant, address the underlying problem and regrout as appropriate.
A discoloured but sound joint is a different problem from a wet wall with loose tiles. Treat them differently instead of trying to bleach away warning signs.
Start with a mild cleaning solution
For suitable ceramic or porcelain tiling with sound cement grout, warm water and a small amount of mild pH-neutral cleaner are a reasonable first step.
Apply with a soft cloth or suitable brush, letting it wet the dirty surface briefly. Avoid flooding the wall or floor, particularly where you suspect failed joints.
Tile specialists such as Mapei advise selecting products compatible with both grout and tile. A cleaner that works on porcelain might etch natural stone or harm a sealant.
Use the right kind of brush
A small nylon grout brush makes it easier to work along joints without scraping a broad area of tile. Choose a brush with enough stiffness to lift dirt but not so hard that it removes grout.
Work in short sections with controlled strokes. Scrubbing one line for several minutes with extreme force is more likely to damage a weak joint than a gentle repeated cleaning.
Avoid wire brushes and metal picks. They can scratch glazed surfaces, mark softer stone and gouge cement grout.
Rinse away the loosened dirt
Wipe or rinse with clean water as appropriate, then use a dry cloth to remove dirty residue. If you leave a soapy film, the lines may attract dirt again.
Change your cleaning water frequently. A bucket that has turned grey is not an effective final rinse.
On floors, dry the surface before anyone walks across it. Cleaning solution on smooth tiles can be slippery.
What about white grout that has turned grey?
Grey appearance often comes from embedded dirt, soap scum or accumulated cleaning residue. Start by making sure you have removed the ordinary film before trying a specialist product.
If the grout is unsealed and porous, staining may extend below the surface. It may improve but not return to its original bright white colour.
Don't keep increasing chemical strength after the improvement stops. Sometimes the realistic options are professional cleaning, recolouring with an appropriate grout colourant or replacing the grout.
Black spots in shower grout
Black spotting can be surface mould or staining associated with damp conditions. Clean with a suitable product approved for the tile and grout system and address the moisture that allowed it to develop.
Improve bathroom ventilation, use the extractor fan and dry wet areas after showering. If the wall remains constantly damp, check for leaks or condensation problems.
Never mix bleach with acidic descalers or ammonia. These combinations can release hazardous gases. Follow the label on any mould cleaner and wear the specified protection.
Don't assume vinegar is harmless
Vinegar is often suggested as a cheap universal grout cleaner. Its acidity can affect cementitious grout over time and is especially risky on acid-sensitive natural stone.
Use an acid-based product only if the tile and grout manufacturers approve it for the particular job. Always follow dilution and rinsing instructions.
A label saying 'natural' doesn't prove a cleaner is non-damaging. Material compatibility matters more than whether the ingredients came from a kitchen cupboard.
Cleaning floor grout
Vacuum or sweep loose grit from the floor first. Otherwise scrubbing can drag abrasive particles over the tile.
Clean a small section of grout lines, rinse and remove the dirty liquid before moving on. A wet vacuum may be useful on suitable floors if used according to its instructions.
Don't leave large quantities of water standing on a floor with damaged grout or questionable waterproofing. A damp mop and careful spot cleaning are often sufficient for maintenance.
Cleaning grout around a kitchen splashback
Grease can be the main problem rather than limescale. Start with a mild compatible degreasing solution and a soft nylon brush.
Take care near electrical sockets and appliances. Never spray liquid directly into outlets or exposed electrical fittings.
Rinse without saturating the wall. Kitchen grout may look much cleaner after removing a thin grease layer that held dust against it.
What if the tiles are natural stone?
Stone such as limestone, travertine and marble may need a specialist pH-neutral cleaner. Acidic products can etch the stone, producing permanent dull patches.
Check whether the stone and grout have been sealed and which product was used. Cleaners that strip sealers may create uneven appearance and require professional correction.
Test any compatible product in a discreet area before treating the entire shower or floor. A small safe trial is better than discovering a problem across twenty square metres.
Are steam cleaners safe?
Some steam cleaners are advertised for grout lines, but heat and pressure may be unsuitable for certain tile, sealer or grout installations.
Consult the equipment and surface manufacturer's advice. Directing concentrated steam at cracked joints or loose tiles can introduce additional moisture where it isn't wanted.
For regular household cleaning, a mild solution and a nylon brush may be safer and more predictable.
Should you seal grout afterwards?
Some cement-based grouts benefit from an appropriate penetrating sealer, while epoxy and other formulations may not need or accept one.
A sealer can reduce how quickly some stains penetrate, but it won't waterproof a failed shower installation or repair cracks.
Follow the grout manufacturer's recommendations, allow new or cleaned grout to dry fully and apply the correct product if required. Never seal over active mould or trapped moisture.
Fixing persistent yellow or brown stains
Brown marks may be rust, mineral deposits, cleaning residue or moisture migrating through the substrate. Each has a different cause.
Identify the likely source before buying stain removers. For example, a leaking metal fitting may continue staining the joint no matter how often you clean it.
If the mark keeps returning with damp patches, investigate plumbing or waterproofing. A cosmetic cleaner is not a substitute for fixing a leak.
Preventing the dirt returning
In showers, squeegee tiles and improve ventilation after use. Wipe soap residue from lower wall sections before it becomes thick.
On floors, sweep regularly so grit doesn't work into the joints. Use compatible cleaning products and rinse away residue.
Avoid using excessive detergent. More product can leave more film, which makes the grout appear dirty again.
When to stop cleaning and repair
Grout that flakes away under gentle brushing, large cracks or loose tiles need attention before another deep clean. Regrouting may be necessary after investigating the cause.
Likewise, mould growing beneath failed silicone may call for removing and replacing the sealant properly, not painting cleaner across its surface.
For ordinary dirt, the rule is simple: identify the tile and grout, start mild, brush gently, rinse and dry. That avoids turning a small appearance problem into a damaged surface.