If you've noticed the silicone around your shower, bath, or basin turning black, lifting at the edges, or peeling away in strips, you're not alone. It's one of the most common bathroom problems we see, and in most cases it's completely fixable without replacing your tiles.
Here's exactly why it happens and what you can do about it.
What causes shower silicone to go black?
The black discolouration you see on silicone is mould, specifically Stachybotrys and Cladosporium species, which thrive in wet, warm environments. Shower silicone is the perfect breeding ground because:
- It stays damp for long periods after each use
- Soap scum and body oils provide nutrients for mould to feed on
- Bathrooms are typically warm, accelerating mould growth
- Silicone has a slightly porous surface that mould can penetrate over time
Once mould has grown into the silicone itself (not just on the surface), no amount of bleach or scrubbing will shift it permanently. The black staining comes back within weeks because the mould roots are embedded inside the sealant.
Key point: Surface cleaning removes visible mould temporarily, but if the silicone has turned black inside, the only real fix is to remove it and apply fresh silicone.
Why does silicone start peeling and lifting?
Black mould is one problem and peeling silicone is another, though the two often go together. There are a few reasons silicone pulls away from surfaces:
1. Poor surface preparation when it was first applied
If the surface wasn't completely clean and dry before the silicone was applied, adhesion is compromised from day one. Grease, soap residue, old silicone, or moisture trapped underneath all prevent a proper bond. The silicone looks fine initially but begins lifting within months.
2. Movement in the structure
Baths and shower trays flex slightly under the weight of water and a person. If the silicone joint isn't flexible enough, or was applied too thinly, this movement causes it to crack and separate from the tiles or tray over time.
3. Using the wrong type of silicone
Not all silicone is the same. Standard decorator's silicone is not suitable for wet areas as it breaks down with prolonged water exposure. Only bathroom-grade or sanitary silicone with anti-mould additives should be used in showers and around baths.
4. Age
Even properly applied, high-quality silicone has a lifespan. Most bathroom silicone lasts between 5 and 10 years before it starts degrading. If your bathroom is older than that and the silicone has never been replaced, it's likely past its best.
Can I just apply new silicone on top of the old?
No, and this is a mistake that causes more problems than it solves. Applying fresh silicone over old silicone means the new layer bonds to degraded material, not the tile or bath itself. It looks fine briefly but peels away much faster, and any mould in the old layer continues to grow underneath.
The old silicone must be completely removed first. This requires a silicone remover, a scraper, and patience. If any residue is left, the new application won't bond properly.
How to prevent silicone going black
Once you have fresh silicone fitted, a few habits will keep it in good condition for much longer:
- Ventilate after every shower. Open a window or run the extractor fan for at least 15 minutes after use.
- Wipe down the silicone. A quick wipe with a dry cloth after showering removes standing moisture.
- Use a bathroom spray weekly. A diluted white vinegar spray or a bathroom anti-mould spray helps prevent mould taking hold.
- Avoid harsh abrasive cleaners on silicone. These break down the surface and make it more porous over time.
When should you call a specialist?
If the silicone is black throughout, lifting away, or has been leaking (causing water staining on walls or ceilings below), it needs to be replaced professionally. DIY silicone jobs are notoriously tricky to get right. Getting a clean, straight bead that bonds properly and looks professional takes practice and the right tools.
A professional silicone replacement typically takes 1 to 2 hours, costs far less than a bathroom refit, and when done correctly will last years before needing attention again.
At Ultra-Seal, silicone replacement is one of our most common jobs. We remove all old sealant, prepare the surface properly, and apply a fresh, neat bead of premium sanitary silicone in whatever colour matches your tiles. Most jobs are done the same day.