Updated
Black Mould On The Kitchen Sealant
The silicone behind the worktop or around the sink has gone black or grey, and cleaning it no longer works.
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What's happening?
Kitchen sealant grows mould where it stays damp. The black is a colony living in the surface of the silicone, which is why bleach lightens it for a week and then it comes back — the roots are below the surface and cleaning only takes the top off. What keeps it damp is the real question. A seal that has shrunk, split or lifted lets water sit behind it, and a kitchen that is not extracting steam properly leaves every cool surface damp for hours after cooking. GOV.UK guidance on damp and mould in the home is direct that mould exposure carries health risks and that the underlying moisture cause has to be addressed, not just the visible growth. So re-sealing without fixing the moisture is a repair that lasts a few months.
What usually causes it?
- The sealant bead split, shrunk or lifted from the worktop or the wall, trapping water behind it
- Non-mould-resistant or general-purpose sealant used in a wet area
- Sealant applied over a damp or dirty surface, so it never bonded properly
- A worktop that moves slightly against a rigid bead, cracking it open
- Kitchen steam not being extracted, so the whole run stays damp after cooking
- Standing water left along the back edge of the worktop after washing up
- A slow leak behind the sink or from an appliance keeping the area permanently wet
Is it dangerous?
Mould in the home is a health matter, not just a cosmetic one — GOV.UK guidance sets out the respiratory and other health risks of exposure and directs that the moisture cause is identified and dealt with. In a kitchen, black sealant is also often the first visible sign of a leak behind it or a ventilation problem, both of which are doing damage out of sight.
Can I fix it myself?
Re-sealing is within reach: cut the old bead out completely with a sealant knife rather than scraping the top off, clean and dry the joint thoroughly, and run a new bead of a mould-resistant kitchen sealant. Keep the surface dry while it cures. What you should not do is run new silicone over old — the mould carries straight through into the new bead and it is black again within months.
When should you call a kitchen fitter?
Call a kitchen fitter when the mould keeps returning after a proper re-seal, when there is swelling in the worktop or the units behind the sealant, or when the joint keeps cracking because the worktop is moving. Have the extraction checked too, since a kitchen that does not clear its steam will make every seal in the room fail early.
What will the kitchen fitter actually do?
- Cut out the old sealant completely and inspect the substrate behind it for water damage
- Trace the moisture source — a failed seal, a leak, a moving worktop or poor extraction
- Dry the joint fully and prepare both faces before any new sealant goes near it
- Re-seal with a mould-resistant kitchen sealant, sized to the joint so it can flex without splitting
- Fix the movement or the extraction problem so the new seal is not doing the same job again next year
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