Silicone sealant is commonly used around showers, baths, basins, sinks and other wet areas because it provides a flexible, water-resistant seal between surfaces.
But even good-quality silicone can eventually develop unsightly black mould, particularly in bathrooms and other areas that remain warm and damp.
If the silicone around your shower or bath is turning black, understanding why mould develops on and around siliconeis the first step towards preventing it from coming back.
Mould thrives in environments with moisture, warmth, and organic material to feed on.
Bathrooms provide almost perfect conditions.
Steam from showers increases humidity, water remains on surfaces, and soap residue, body oils and other contaminants can collect along silicone joints.
Although the silicone itself may be water resistant, contaminants sitting on its surface can provide conditions where mould can grow.
Several factors can make the problem worse.
One of the biggest contributors to bathroom mould is excessive moisture.
After a hot shower, condensation can remain on tiles, glass, grout and silicone for extended periods.
Without adequate ventilation, the moisture takes longer to evaporate.
Over time, consistently damp silicone joints can become an ideal place for mould to grow.
Use your bathroom exhaust fan while showering and leave it running afterwards to help remove humid air.
Where practical, open a window or door to improve airflow and allow wet surfaces to dry more quickly.
Silicone around the bottom of showers, baths and basins is regularly exposed to water.
If the area doesn’t drain or dry properly, water can remain against the silicone for long periods.
Persistent moisture increases the likelihood of mould developing.
After using a shower, removing excess water from the shower screen and surrounding surfaces can help the area dry faster.
It isn’t necessarily the silicone itself that mould is feeding on.
Soap residue, shampoo, body oils and other contaminants can accumulate on the surface of the silicone.
These deposits combined with moisture create favourable conditions for mould growth.
Regular cleaning helps prevent this build-up.
Pay particular attention to corners and edges where residue tends to collect.
Silicone doesn’t last forever.
Over time it can become damaged, discoloured, cracked or begin separating from the surface.
Once this happens, water and contaminants can become trapped around or behind the joint.
If mould appears to be inside or underneath the silicone rather than simply sitting on the surface, cleaning alone may not solve the problem.
You may need to remove and replace the silicone.
Surface preparation is extremely important when applying silicone.
Applying new silicone over dirty, damp or contaminated surfaces can prevent proper adhesion.
If gaps develop between the silicone and the adjoining surface, moisture can become trapped behind the seal.
Before applying new silicone, prepare the joint properly according to the sealant manufacturer’s instructions.
If mould is only present on the surface and the silicone is otherwise in good condition, cleaning may be sufficient.
Use a cleaning product suitable for the silicone and surrounding surfaces and follow the product manufacturer’s instructions.
Avoid aggressive scrubbing tools that could damage the silicone joint.
After cleaning, rinse the area where appropriate and allow it to dry thoroughly.
If staining remains after cleaning, or mould appears to be growing underneath the silicone, replacement may be the better option.
Continuing to clean badly deteriorated silicone won’t repair a failed joint.
Consider replacing the silicone if you notice:
Removing the old silicone also gives you an opportunity to inspect and properly prepare the joint before resealing it.
Generally, simply applying another layer over mouldy or deteriorated silicone isn’t a good solution.
The new silicone needs a suitable surface to adhere to, and covering the existing problem can trap contamination and moisture underneath.
For a proper repair, the deteriorated silicone should normally be removed and the surfaces thoroughly cleaned and dried before new sealant is applied.
Always follow the instructions supplied by the manufacturer of the silicone you’re using.
Preventing mould largely comes down to controlling moisture and keeping the silicone surface clean.
A few simple habits can make a significant difference:
Not every sealant is designed for every application.
When sealing showers, baths, basins and other wet areas, choose a product specifically recommended by its manufacturer for the intended application.
Some sanitary and bathroom silicones contain additives designed to resist mould growth, but this doesn’t mean the joint can never develop mould.
Ventilation, cleaning and moisture management are still important.
A neat silicone joint isn’t just about appearance.
Consistent application helps create a properly formed joint without unnecessary gaps and irregular areas where moisture and grime can accumulate.
Before applying silicone:
Some of the most difficult silicone joints to clean and maintain are also the hardest ones to seal correctly in the first place.
Behind basins, beside vanities, around baths and in tight internal corners, a standard silicone nozzle may not provide enough reach or the correct application angle.
Rather than forcing the caulking gun into an awkward position, a purpose-designed extension or angled nozzle can help deliver the sealant where it’s needed.
Proline Sealants offers Extension Caulking Nozzles that can be screwed together for additional reach, along with 45–90° Corner Nozzles for difficult angles and confined spaces.
Black staining on shower silicone is commonly associated with mould growth. Bathrooms provide the moisture and humidity mould needs, while soap residue and other contaminants can accumulate on the silicone surface.
Not necessarily. Surface mould doesn’t automatically indicate a leak. However, if the silicone is cracked, separating or mould appears to be underneath it, the joint should be inspected more closely.
Yes. If moisture gets behind a poorly bonded or deteriorated silicone joint, mould and staining may develop beneath or around the sealant.
If the mould is only on the surface and can be cleaned successfully, replacement may not be necessary. If the silicone is damaged, separating, badly stained or mould is underneath it, removing and replacing the silicone may be the better solution.
Good ventilation, regular cleaning, reducing standing moisture and keeping silicone joints in good condition can all help reduce mould growth.
Mouldy silicone isn’t always a sign that the silicone itself has failed.
Often, the combination of moisture, poor ventilation and surface contamination creates the conditions that allow mould to develop.
Keeping wet areas ventilated, cleaning silicone regularly and addressing deteriorated joints early can help keep bathrooms and kitchens looking cleaner for longer.
And when it’s time to reseal those difficult-to-reach areas, having the right caulking nozzle can make the application considerably easier.
Proline Sealants – Screw together. Reach further. Get the job done.