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Silicone around a bath tool, without a leak path

Updated: 21 October 2026

The black line around your bath looks like dirt, and a neat new bead will not fix it if the old silicone stays in the joint or the bath was empty when you sealed it. A silicone around bath tool only profiles what you have already prepared. This page is the wet-room job: a bath, a shower tray, or a sink, including a mouldy bead. Window frames stay out of it. The generic pass is on [how to use a sealant finishing tool](/hub/flooring-tools-and-accessories/joint-smoother/sub/joint-smoother-how-to-use). Kits and prices are on the [joint smoother comparison](/hub/flooring-tools-and-accessories/joint-smoother). Peter F. did not reseal a bath in a lab. A qualifying amazon.co.uk purchase can earn a commission at no extra cost to you.

The black line around your bath looks like dirt, and a neat new bead will not fix it if the old silicone stays in the joint or the bath was empty when you sealed it.

Our top picks

Presch Presch sealant finishing tool set, 5 pieces

Best overall

Presch Presch sealant finishing tool set, 5 pieces
8.3/10about £9.99
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RAVN HAMAN RAVN HAMAN 5-piece sealant finishing set

Best value

RAVN HAMAN RAVN HAMAN 5-piece sealant finishing set
7.2/10about £5.39
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ORHOMELIFE ORHOMELIFE 11-piece caulking tool kit

Alternative

ORHOMELIFE ORHOMELIFE 11-piece caulking tool kit
7.2/10about £11.89
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On this page
  1. 1.When the black bead is more than a stain
  2. 2.Strip the old joint without wrecking the bath
  3. 3.Fill, gun, and profile
  4. 4.Corners, cure, and when to stop

When the black bead is more than a stain

Mould in bathroom silicone sits in the bead, not on it. Mills Building Consultancy's note is that the spots are inside the silicone, so a bleach wipe leaves the colony in place. Cut the bead out, dry the gap, and seal again with a sanitary silicone that carries a fungicide. Water behind a failed joint can reach joists and the ceiling below. A brown stain on that ceiling, or a soft patch beside the bath, means the profiler is no longer the first tool. Wear goggles, gloves and a mask while you cut. Uttlesford District Council's advice is not to brush mould, because brushing throws it into the room. The finger-versus-paddle argument is on smooth silicone with a finger or a tool.

Strip the old joint without wrecking the bath

Glazed tile and glass can take a metal scraper if you keep the blade flat and you do not dig at the glaze. Plumbing Superstore's reseal note says scrape, then white spirit, and do not scratch the tile. ORHOMELIFE's UK reviews describe a scraper lifting old silicone from tiles, sinks and baths. That is the hard surface. It is not a permission slip for acrylic. An acrylic bath marks under a stainless blade. Cramer's Kit 7 method keeps the knife off acrylic. A buyer in the Stone Reef file kept the metal blades off plastic shower walls and used a plastic scraper. After the bead is out, the gap has to be dry and free of grease, soap film and white-spirit residue. Do not gun onto a rim you have just wiped with washing-up liquid. UniBond's cure times belong to that tube only.
Presch Presch sealant finishing tool set, 5 pieces

Testsieger

Presch Presch sealant finishing tool set, 5 pieces
8.3/10about £9.99
View offer

Fill, gun, and profile

Fill the bath and leave it full while you seal and while the bead cures. Plumbing Superstore states that step, and Mills explains why: the joint is at its widest when the bath is loaded. Seal an empty acrylic or steel bath and the next fill can pull the fillet off one face. A shower tray does not need filling in the same way. A basin usually does not either, unless it is a large plastic bowl that moves when it is full. Gun a sanitary silicone with a fungicide, not a decorator's sealant left from a skirting board. Cut the nozzle with the bath still full, and tool one pass with light pressure. A 16 mm sweep on a 5 mm gap leaves a shelf that holds water. If the old bead is still in place, you want a remover as well as finishers. That choice is on the buying guide.

Corners, cure, and when to stop

Do the three-way corner in an order. Cramer's method is verticals first, leave those beads to bond, then run the rim joint outwards from the corner. Guides keep the smoother out of the grout where the walls meet the rim. If you tool the horizontal bead first, the verticals smear across it. Cure time is on the cartridge. Plumbing Superstore, Checkatrade and the UniBond sanitary sheet use about 24 hours for that tube, and another brand can differ. Do not shower, and do not empty the bath as a test, until that cure has passed. Emptying it halfway lets the rim rise and stress the skin. Stop if the ceiling below is stained or the floor is soft. A new bead will not dry a joist, and this page will not promise the black spots never return.

Common questions

Should the bath be full?
Yes. Fill it and leave it full while you seal and while that bead cures. The rim sits lower under the water, so the joint is at its widest. Seal it empty and the next proper bath can pull the fillet off one face. A shower tray is different. You are not filling a tray to stretch it. You are still sealing onto dry, clean faces.
How do I get mouldy silicone out?
Cut the whole bead out. The mould is in the silicone, so a surface wipe leaves it behind. Use a plastic scraper on acrylic and keep metal for glaze you can work without digging in. Wear goggles, gloves, and a mask, and do not brush the spores around the room. Dry the empty gap before you gun. White spirit can lift residue on tile. It is not a soak for acrylic.
Can I use the metal scraper on an acrylic bath?
No. A stainless blade marks acrylic, and the kit listings that say the plastic tools will not scratch tiles do not clear the blades for a plastic bath. Use a plastic scraper, even if it is slower. Cramer's own method keeps the knife off acrylic. Glazed wall tile is the surface where a careful metal blade is the usual DIY approach.
How long before a shower?
Follow the cartridge you opened. About 24 hours is the figure Plumbing Superstore, Checkatrade, and the UniBond sanitary sheet use, and the UniBond time is for that tube. Another brand can differ. Keep the bath full during the wait if you sealed it full. A shower that wets the bead early is how a tidy fillet peels in the first week.
Do I need a fungicidal sanitary silicone?
Yes for a bath, shower, or sink. Mills's repair is a sanitary silicone with a fungicide after the old bead is gone and the joint is dry. A general-purpose sealant from another job is the wrong tube. Fungicide does not make up for silicone left in the gap, and it does not promise the mould will never come back if the room stays wet and unventilated.

Related pages

Best sealant finishing tool

Joint smoother

Silicone profiling kit: fan, profile set or remover

Smooth silicone with finger or tool for a wet room

How to use a sealant finishing tool on a dry joint

Sources

Public UK sources from the research digest. Listing prices, stars and review counts are the amazon.co.uk lines used for this comparison, retrieved 19 October 2026.

  1. GOV.UK — General Product Safety Regulations 2005: Great Britain (retrieved 19 October 2026)
  2. legislation.gov.uk — General Product Safety Regulations 2005 (retrieved 19 October 2026)
  3. GOV.UK — Consumer Rights Act 2015 (retrieved 19 October 2026)
  4. BSI Knowledge — BS EN ISO 11600:2003+A1:2011 (retrieved 19 October 2026)
  5. Cramer UK — Profiling Kit 7 (retrieved 19 October 2026)
  6. wolfcraft — Joint smoother fan set 4332000 (retrieved 19 October 2026)
  7. Henkel — UniBond sanitary sealant UK datasheet (retrieved 19 October 2026)
  8. Uttlesford District Council — Removing mould (retrieved 19 October 2026)