Quick answer: Make a paste from bicarbonate of soda and white vinegar, apply it to the mouldy sealant, and leave for five to ten minutes before scrubbing with an old toothbrush. For stubborn mould, spray a diluted bleach solution and leave for fifteen to thirty minutes instead. If the mould keeps coming back or has spread beneath the surface, the sealant likely needs replacing rather than cleaning.
Black mould on bathroom or kitchen sealant is one of those problems that seems to appear overnight and then refuses to budge. It thrives in the warm, damp conditions around baths, showers, and sinks, and beyond looking unpleasant, it is worth taking seriously since prolonged exposure can affect respiratory health. This guide covers how to clean it properly, when cleaning is not enough, and how to stop it coming back.
Why Mould Grows on Silicone Sealant
Silicone sealant around baths, showers, and sinks is constantly exposed to moisture, soap residue, and warmth, which together create an ideal environment for mould spores to settle and multiply. Poor ventilation makes this worse, since steam and humidity have nowhere to escape after a bath or shower.
Signs of Mould on Sealant
- Small black or dark green spots along the sealant line
- A musty smell in the bathroom, sometimes noticeable before any visible spots appear
- Larger black areas in more advanced cases, which often indicate the mould has been present for some time
What You Will Need
- Rubber or chemical-resistant gloves
- A face mask, particularly important if using bleach
- An old toothbrush or stiff-bristled brush
- Bicarbonate of soda and white vinegar, or a dedicated mould remover spray
- A microfibre cloth
Method 1: Bicarbonate of Soda and Vinegar
This natural approach is a good first attempt for mild to moderate mould, without the smell or harshness of bleach.
- Mix one cup of white vinegar with two to three teaspoons of bicarbonate of soda to form a paste.
- Apply the paste generously to the mouldy areas using a damp cloth.
- Leave it to sit for five to ten minutes, longer if the mould is more established.
- Scrub in circular motions with an old toothbrush, working into any grooves in the sealant.
- Rinse with a cold, damp sponge and dry the area thoroughly with a microfibre cloth.
Method 2: Bleach Solution
For tougher, more ingrained mould, a diluted bleach solution is more effective at killing spores rather than just lifting the visible stain.
- Mix one part bleach with four parts water in a spray bottle.
- Ventilate the room well before you start, opening a window if possible.
- Spray the solution generously over the affected sealant and leave it to sit for fifteen to thirty minutes.
- Scrub gently with a brush, then rinse thoroughly with clean water.
- Dry the area completely, since any remaining moisture will encourage the mould to return.
Never mix bleach with other cleaning products, particularly anything containing ammonia, since this can produce dangerous fumes.
Method 3: Dedicated Mould Remover Spray
A good-quality mould remover spray with an active biocide, rather than just a bleach-based stain remover, is often the most reliable option for silicone sealant specifically. Look for a product that states it kills mould spores rather than simply masking the stain, since this reduces the chance of it returning in the same spot. Follow the product’s instructions and safety advice closely, particularly around ventilation and contact time.
When Cleaning Isn’t Enough: Time to Reseal
Sometimes mould has grown into the sealant itself rather than sitting on the surface, in which case no amount of scrubbing will fully remove it. Signs it is time to replace the sealant rather than keep cleaning include mould that returns within days of cleaning, dark staining that does not lift even after scrubbing, or sealant that has become cracked, shrunk, or is starting to peel away from the surface.
How to Reseal After Removing Old Sealant
- Cut along both edges of the old sealant with a utility knife or a dedicated sealant remover tool.
- Peel away the old sealant fully, using a scraper for any stubborn residue.
- Clean the area thoroughly with a mould and mildew cleaner, then let it dry completely.
- Apply masking tape along both edges of the gap for a neat finish line.
- Apply the new sealant with a caulk gun in a steady, continuous line.
- Smooth the bead with a silicone finishing tool or a wet finger before it starts to skin over.
- Remove the masking tape while the sealant is still fresh, then leave it to cure fully according to the product’s instructions before getting it wet.
Choosing a mould-resistant sealant with built-in fungicide additives for the replacement will help delay mould returning compared with standard sealant.
Preventing Mould From Coming Back
- Open a window or run an extractor fan during and after every bath or shower to clear humidity quickly.
- Wipe down the sealant and surrounding tiles with a dry cloth after use, since mould struggles to establish on a dry surface.
- Wash shower curtains, bath mats, and towels regularly, since these can harbour spores that spread back onto the sealant.
- Choose a mould-resistant sealant when resealing, rather than a standard silicone.
Related Guides
- How to Remove Old Caulk or Silicone Sealant (if the sealant needs full replacement rather than cleaning)
- How to Clean Grout
Frequently Asked Questions
Can black mould on sealant be permanently removed?
Surface mould can usually be cleaned effectively with the methods above. If the mould has grown into the sealant itself, cleaning will only be a temporary fix and the sealant will need replacing for a permanent result.
Is mould on silicone sealant dangerous?
It can affect health with prolonged exposure, particularly for people with asthma, allergies, or other respiratory sensitivities, so it is worth addressing promptly rather than leaving it to spread.
How do I stop mould coming back on bathroom sealant?
Good ventilation is the biggest factor. Opening a window or running an extractor fan after every bath or shower, and wiping the sealant dry afterwards, makes a significant difference.
When should I replace sealant instead of cleaning it?
If mould returns within days of cleaning, or the sealant is cracked, peeling, or shrinking away from the surface, cleaning alone will not solve the problem and it is time to reseal.
Final Thoughts
Most mould on silicone sealant responds well to a bicarbonate of soda and vinegar paste or a diluted bleach solution, provided you catch it early and dry the area thoroughly afterwards. If mould keeps returning despite regular cleaning, replacing the sealant with a mould-resistant version, alongside better ventilation, gives a much longer-lasting result.