White bathroom silicone when the old bead has gone black
Updated: 23 October 2026
You are replacing a black or stained line on a white bath, shower or basin, and you want the new bead to stay pale. White bathroom silicone can do that only if the cartridge states a fungicide, the old bead is cut out, and soap does not sit on the new one. A fungicide slows mould in the sealant. It does not clean the face of the bead, and it does not replace the extractor fan. The [Silicone white comparison](/hub/fillers-adhesives-and-sprays/silicone-white) is the product table. Prices are the 21 October 2026 snapshot. A qualifying purchase through our amazon.co.uk links can earn us a commission at no extra cost to you.
You are replacing a black or stained line on a white bath, shower or basin, and you want the new bead to stay pale.
You are replacing a black or stained line on a white bath, shower or basin, and you want the new bead to stay pale. White bathroom silicone can do that only if the cartridge states a fungicide, the old bead is cut out, and soap does not sit on the new one. A fungicide slows mould in the sealant. It does not clean the face of the bead, and it does not replace the extractor fan. The Silicone white comparison is the product table. Prices are the 21 October 2026 snapshot. A qualifying purchase through our amazon.co.uk links can earn us a commission at no extra cost to you.
Our top picks
| Badge | Product | Fungicide line | Stars and reviews | Cure on the listing | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Unibond UniBond Triple Protection silicone, white, 291 g | Anti-mould | 4.6 from 4,120 | 20 min / 24 h | 9.4 | about £13.49 | View offer |
 Sika Sika sanitary silicone, white | Mould resistant | 4.5 from 10,620 | Not stated | 9.6 | about £7.69 | View offer | |
| Best value |  Sika Sika general purpose silicone, white | Anti-fungal, no class digit | 4.5 from 7,959 | Not stated | 9.4 | about £5.00 | View offer |
On this page
What a bathroom bead is for
BS EN 15651-3 covers interior joints in bathrooms, showers and domestic kitchens, and non-pressurised water. It does not cover swimming pools, drinking water or food contact, and it does not tell you how to gun the bead. A 70 g tube that only says waterproof has not said any of that.
Sika sanitary and UniBond are written as bath cartridges. Dowsil 785 names baths and showers. Sika general purpose lists shower as a surface. The 151 tube at about £3.35 is filed as repair. Siroflex puts bathrooms in a title that is really about windows and 12.5 percent movement. If the joint is a uPVC frame, leave this page. If it is the black line under the rim, ask whether the listing states a fungicide.
Fungicide is not a cleaning contract
Soudal's FAQ says the fungicide does not stop mould on soap film, grease and damp dust sitting on the bead. Warmth and a weak fan make that film worse, and the fungicide in the sealant is used up over time. A monthly wipe is a maintenance line, with the label's own conditions. It is not a result measured on these twelve cartridges.
A bead that has gone black inside has to be cut out. UniBond's listing says the silicone repels, kills and prevents mould. That is UniBond's wording, not a white bead for life. Wipe the joint after showers and run the fan. If you will not, a dearer cartridge still blackens on the surface.
Which listings in this set state it
Sika sanitary (about £7.69) says mould resistant. Sika general purpose (about £5.00) says anti-fungal, with no class digit. UniBond (about £13.49) says anti-mould and prints 20 minutes and 24 hours. Dowsil 785 says it resists mould. Enócilis says anti-mould, and the reviews say the cure is not solid white.
Both 151 tubes, Siroflex and the Shopstop kit do not state a fungicide. None of the twelve prints an S1 digit. Anti-mould is the phrase on the page, not the higher class code.
When the chemistry changes
Glazed ceramic and glass are the acetoxy pattern in trade notes. Dowsil 785 names acetoxy, and its sheet excludes natural stone. Test acrylic in a hidden spot, because a vinegar-cure bead can mark a rim. Everbuild 500 lists PVCu, so there is no rule that every acetoxy cartridge ruins plastic.
UniBond's sheet is alkoxy neutral, with a stone claim the amazon file does not repeat. Follow the sheet on marble. A general-purpose white at about £5.00 can be enough for a low-risk ceramic gap. It is a weak stand-in when the surround is stone or the old bead failed in a power shower.
After you choose
Cut the old bead out, wipe with white spirit, dry the joint, fill the bath, and tool while the paste is wet. Where the listing is blank, wait at least 24 hours. UniBond prints 20 minutes and 24 hours. Twenty minutes is touch dry, not a shower. The order of that cut is on the how to apply silicone sealant page.
Then wipe the face of the bead. Ventilate an acetoxy smell while it cures. A white sanitary cartridge is still the wrong movement class for a frame, even when the fungicide line is the strongest in this set.
Common questions
Which white silicone for a shower?
Choose a listing that states a fungicide and names a bath or shower. Sika sanitary at about £7.69 has 4.5 from 10,620 reviews and a mould-resistant title. UniBond adds 20 minutes and 24 hours. The £3.35 151 tube states no fungicide, so it is the short repair, not the shower bead.
Why did anti-mould silicone go black?
Usually because soap and moisture sat on the bead, or the old silicone was left underneath. Soudal says the fungicide does not stop mould on that film. A black line inside the sealant has to be cut out. A different brand will not cancel a dirty joint.
Can you clean black mould out of the bead?
You can bleach the face, and you cannot clean mould that has grown through the rubber. Surface stain is a wipe, with the cleaner the label allows. Mould inside the section means cutting the bead out, degreasing with white spirit, drying, and sealing again. A skim of new silicone over the black line peels along the old edge.
Is general-purpose white silicone enough?
Sika general purpose at about £5.00 states anti-fungal ingredients and names showers, with no class digit. It can be enough for a ceramic gap you will keep clean. It is a weaker choice when the bead has already failed and you wanted a cartridge sold as sanitary.
Does the fungicide mean you can skip the extractor fan?
No. The fungicide is in the sealant. The fan, and a wipe after showers, deal with the soap film where mould starts. Soudal is explicit that an anti-mould cartridge still grows mould on residue. The cartridge and the fan do different jobs.
Acrylic bath or glazed tile: same cartridge?
Often the same sanitary cartridge, with a test on acrylic. Glazed tile suits the acetoxy pattern Dowsil 785 states. Natural stone changes the tube: Dow's sheet excludes it, and UniBond's sheet claims it while the amazon listing stays silent.
Related pages
Sources
Public UK sources used for this comparison. amazon.co.uk prices, stars and review counts were taken from the listings on 21 October 2026.
- BSI, BS EN 15651-3:2017 sanitary sealants (retrieved 21 October 2026)
- GOV.UK construction products regulation in Great Britain (retrieved 21 October 2026)
- GOV.UK acetic acid general information (retrieved 21 October 2026)
- Sika Everbuild Everflex 500 bath and sanitary silicone (retrieved 21 October 2026)
- Sika Everflex 500 EN 15651-3 declaration of performance (retrieved 21 October 2026)
- DOWSIL 785 sanitary acetoxy silicone technical data sheet (retrieved 21 October 2026)
- Bostik SX Contractors LMN silicone technical data sheet (retrieved 21 October 2026)
- UniBond Triple Protection technical data sheet (retrieved 21 October 2026)
- Soudal UK, acetoxy and neutral silicones (retrieved 21 October 2026)
- Soudal UK, painting over silicone sealant (retrieved 21 October 2026)
- Screwfix, how to silicone a shower (retrieved 21 October 2026)
- Toolstation sealant buying guide (retrieved 21 October 2026)