Why is my bathroom grout turning black?
Black marks on bathroom grout are often mould growing where moisture lingers. Cleaning can remove the visible problem, but better drying and ventilation are usually needed to stop it returning.
Why does mould grow on grout?
Grout lines regularly collect water, soap residue and skin oils. In a warm room that stays damp after bathing, this gives mould the conditions it needs. Areas with little airflow, such as corners, behind bottles and around the lower part of a shower, may darken first.
Grout is not necessarily failing just because its surface is stained. However, recurring mould is a sign that the area is staying wet for too long, so it is worth addressing the cause as well as cleaning the marks.
How should I clean black grout?
Start with a bathroom cleaner that is suitable for the tile and grout, following its label carefully. Ventilate the room, wear gloves and test the product on a small hidden area first. A soft brush can help lift dirt without damaging the surface.
Never mix cleaning products, especially bleach with acidic or ammonia-based cleaners, because dangerous fumes can be produced. Avoid harsh scrubbing tools that scratch tiles or wear away grout. Rinse away the cleaner and dry the area afterwards.
How can I stop the black marks coming back?
Run the extractor fan while bathing and leave it on afterwards for the period recommended for your fan. Wipe down wet shower walls, spread towels out to dry and avoid leaving bottles directly against damp grout lines. Keep the room warm enough to dry and open the door after the steam has cleared if this helps air move through the room.
If the fan is weak, very noisy or does not clear condensation, it may need cleaning, adjustment or replacement. Persistent condensation can also mean the fan, air path or room heating needs a closer look.
When does grout need replacing?
Cleaning will not repair grout that is cracked, loose, powdery or missing. Damaged joints can allow more water into the surrounding construction and should be assessed rather than repeatedly covered with fresh grout.
If black staining quickly returns despite good cleaning and drying, or there is a damp smell, loose tile, swollen surface or water appearing outside the bathroom, ask a bathroom professional to investigate. The source may be failed joints, a leak or a waterproofing problem hidden behind the finish.
Quick black-grout checklist
- Use a cleaner approved for your particular tile and grout.
- Never mix bleach or other cleaning products.
- Run the extractor during and after baths or showers.
- Wipe wet surfaces and let towels dry properly.
- Keep bottles and clutter away from damp corners.
- Have cracked, loose or repeatedly stained grout assessed.