Why is my bathroom sealant going mouldy?
Mouldy bathroom sealant is usually a sign that moisture is sitting around for too long. Sometimes it is just cleaning and ventilation. Sometimes it points to a leak, failed seal or poor fitting detail.
Why silicone turns black
Silicone sits at the wettest joints in a bathroom: around baths, shower trays, screens, basins and sometimes worktops. If soap residue, shampoo and moisture stay on the surface, mould can grow on top of the sealant.
Good quality sanitary silicone resists mould better than general-purpose sealant, but it still needs airflow and regular cleaning.
When it is more than normal wear
If the sealant is peeling away, splitting, soft, stained behind the bead, or the wall/floor nearby feels damp, the joint may have failed. Simply putting new silicone over old silicone will not fix trapped moisture.
A shower screen that leaks, a tray with movement, poor falls, tired grout, or weak extraction can all make sealant fail faster.
What you can do first
Keep the bathroom ventilated after showers, wipe standing water from corners, and clean the silicone gently so soap film does not build up. Avoid harsh scrubbing that damages the surface.
If mould keeps returning quickly after cleaning, it is worth checking the ventilation, the shower screen seal, the tray edge and any movement around the bath or shower.
Quick checks for mouldy sealant
- Does the extractor fan run properly and stay on after showers?
- Is water pooling along the tray, bath or screen?
- Is the silicone lifting, cracked or loose?
- Is there staining, swelling or damp below the joint?
- Has new silicone been applied over old silicone?