Black spots along the bath or shower sealant are one of the most common complaints in any bathroom. Some of it wipes away. Some of it won’t move however hard you scrub. The difference is whether the mould is sitting on the surface or has grown into the sealant itself. This guide explains what works, what doesn’t, and when the only real fix is to replace the bead.
Surface mould or mould in the sealant?
Mould needs moisture, warmth and something to feed on. Soap residue, skin cells and body products along a sealant joint give it all three.
Surface mould sits on top of the bead. It often looks like grey or black smudges and lifts when you wipe with a mould cleaner. Mould in the sealant looks like black dots or streaks inside the bead itself. It doesn’t move with cleaning because it is not on the surface any more. Silicone is slightly porous to mould once it is old or damaged, and the growth spreads into it.
What usually works on surface mould
- A bathroom mould remover, used exactly as the label says, with the room ventilated.
- A soft cloth or soft brush. Avoid scouring pads, which roughen the surface and give mould more to grip.
- A thorough rinse and then drying the joint with a towel or squeegee.
Never mix cleaning products, especially bleach-based products with anything acidic. The fumes can be dangerous.
Why bleach and scrubbing often fail
Bleach can lighten black staining, so the bead may look better for a while. But it often can’t reach mould that has grown into the sealant, so the spots come back. Scrubbing hard can scuff the bead, open small cracks and make the problem worse.
If you have cleaned properly two or three times and the black is still inside the bead, it is time to stop cleaning and start planning a replacement. Our longer guide to why sealant goes mouldy goes into the causes.
Need it done properly? Mr Mastic covers the South East, London and Scotland, with a one-year guarantee on every job. Call or email for a quick quote.
The fix: cut it out and start again
Once mould is in the sealant, the lasting fix is to remove the whole bead, clean the joint, treat it and lay new sealant. That is exactly what a bathroom reseal involves. We cut out every bit of the old sealant, treat any mould in the joint, let it dry and apply anti-fungal sanitary silicone such as Everbuild’s.
Anti-fungal silicone resists mould growth, but it is not a guarantee against it. If the room stays damp and the joint stays dirty, mould can still appear in time.
Stopping it coming back
- Ventilate. Run the extractor fan during and after a shower, or open a window.
- Dry the joint. A quick wipe with a squeegee or towel after showering makes a big difference.
- Rinse off product. Shampoo and shower gel left on the bead feed mould.
- Clean little and often with a mild cleaner, rather than an occasional harsh scrub.
See our aftercare tips for more.
Mould on grout as well
If the grout around the bath or shower is also black, the same rules apply. Surface staining on grout often cleans off. Mould deep in old, porous grout may not. Raking out and replacing badly stained grout before resealing gives the new bead clean, sound tiles to sit against.
Quick answers
Is black mould in sealant dangerous?
Mould and damp can affect health, particularly for people with breathing problems or weak immune systems. It is worth dealing with rather than living with.
Can I paint over mouldy silicone?
No. Silicone isn’t paintable, and painting over mould doesn’t remove it. The sealant needs to come out.
How long does new anti-fungal silicone stay clean?
It depends on ventilation, cleaning and use. In a well-ventilated room with regular wiping, it stays clean far longer than in a damp one.
Is mould behind the sealant a sign of a leak?
It can be. Mould that keeps returning, or dampness behind the bath panel, can mean water is getting behind the bead and is worth checking.
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More advice
- Why Does Bathroom Sealant Go Mouldy?
- Looking After New Sealant: Aftercare Tips
- Can You Put New Silicone Over Old Silicone?
- All advice
This guide is general information about sealant work. It isn’t legal, fire-safety or structural advice; for those, speak to a qualified professional.