In short
- Most dark grout is soap scum, body oils, dirt or surface mould, and it cleans up.
- Mould that has grown under silicone, or grout that's cracked or crumbling, needs replacing.
- Sealing cement-based grout helps it resist stains and water.
Why grout goes dark
- Soap scum and body oils in showers build up on the rough grout surface.
- Mould and mildew grow where surfaces stay damp and ventilation is poor.
- Dirt from mopping. Dirty mop water settles in the lower grout lines.
- Unsealed grout. Cement-based grout is porous, so it soaks up whatever lands on it.
Cleaning grout the right way
- Rinse the area to soften the grime.
- Use a cleaner suited to the job: a bathroom cleaner for soap scum, a mould remover for mould.
- Scrub along the grout line with a stiff nylon brush. Wire brushes damage grout and tiles.
- Rinse well, so no cleaner is left in the grout, and dry the area.
Check your tile type first. Acidic cleaners and vinegar can etch marble, limestone and travertine, and bleach can fade coloured grout.
When cleaning won't fix it
| Problem | Usual fix |
|---|---|
| Grout stained right through | Regrouting, or a grout colour sealer |
| Cracked, crumbling or missing grout | Regrouting, and a check for leaks |
| Black spots under the silicone | Removing and replacing the silicone |
| Tiles that sound hollow or move | A tiler, as water may be getting behind them |
A professional clean will lift most discolouration, and a good cleaner will tell you before starting if replacement is the only real fix.
Sealing grout
A penetrating sealer soaks into cement-based grout and makes it resist water and stains. Apply it only when the grout is clean and completely dry. In showers, resealing every year or two keeps it working. Epoxy grout doesn't usually need sealing.
Keeping grout clean
- Improve ventilation: run the exhaust fan during and after showers, or open a window.
- Squeegee shower walls and screens after use.
- Mop floors with clean water, changing it often, and rinse the mop.
- Clean the shower weekly, before soap scum has a chance to harden.
