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Reseal a bath silicone so the bead does not crack

Updated: 23 October 2026

The last bead around your bath or shower tray cracked after a proper soak, or it went black in the corner, and you are about to gun a new one. Reseal a bath silicone only after the joint is stripped and dry, with the bath filled before you gun, and with the water left in until that cartridge has cured. An empty bath, a damp joint or a film of old silicone is how the new line fails. The [joint scraper comparison](/hub/hand-tools/joint-scraper) is for the tool, not the cure. Peter F. has not tested your bath. A qualifying purchase can earn us a commission at no extra cost to you.

The last bead around your bath or shower tray cracked after a proper soak, or it went black in the corner, and you are about to gun a new one.

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On this page
  1. 1.Why the last bead failed
  2. 2.Strip, then dry, then fill
  3. 3.The cartridge, including acrylic
  4. 4.Gun once, then leave the water in

Why the last bead failed

Three causes cover most split or mouldy bath beads. The bath was empty, so the first soak dropped the rim. The joint was damp, so the silicone skinned on water. Or you sealed over old silicone. Mould in the old bead comes away when you strip it. A wet wall behind it is a stop, not a thicker bead. Soudal, Plumbing Superstore and Brewers leave the water in for the cure. Wickes fills the bath before the old sealant comes off. Do not follow that order. Strip and dry first.

Strip, then dry, then fill

Cut and peel the old bead, then clear the film. Dry until the joint does not look or feel damp. An overnight wait is a rule of thumb, not a British Standard. Do not use a dichloromethane stripper in the bathroom. Only then fill the bath, close to the overflow. Keep the water in until the sealant has cured. Soudal’s gap of about 5 mm and Plumbing Superstore’s tape at least 3 mm off the wall are tape positions, not the bead size. Cramer’s removal tool is not for acrylic or plastic.
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The cartridge, including acrylic

Use a sanitary silicone and read the class. Unibond cites type S and F-25LM. Bostik S31 cites XS2. ISO 11600 and BS EN 15651-3 describe the cartridge, not the scraper. A 25% class on a 5 mm joint is 1.25 mm of movement, which is why an empty bath tears a thin bead. illbruck’s practical fillet is about 4–5 mm on each face. Soudal sells Stay Fresh as acetoxy and as neutral. Read the tube before an acrylic bath. If the bath or screen is glass, or the stone is porous, stop. A fungicide does not dry a wet wall.

Gun once, then leave the water in

Gun onto the dry joint while the bath is full, and tool once inside the skin time on that tube. Bostik S31 is about 8 minutes at 23°C and 50% relative humidity, with a wet round-ended tool. Unibond is about 30 minutes. Brewers is about 5 minutes. Pull the tape while the bead is wet, and keep finishing solution out of the bond line. Cure is often about 2–3 mm per 24 hours. Stay Fresh’s sheet is about 2 mm per 24 hours. Leave the water in until the tube says it has cured. Do not empty the bath because the surface feels dry.

Common questions

Why does a new bath bead crack after the first proper soak?
The bath was probably empty when you sealed it. Filling it later drops the rim and tears a bead with little movement left. A 25% class on a 5 mm joint is about 1.25 mm. Seal with the bath already full, leave the water in through the cure, and keep the fillet near 4–5 mm on each face.
Should the bath be full before I scrape, or only before I seal?
Fill it after the joint is stripped and dry, and before you gun. Soudal and Plumbing Superstore leave the water in for the set. Wickes publishes a fill before the old sealant comes off. Do not copy that. You want the rim low for the new bead, not a full bath while you are still cutting.
How dry does the joint need to be?
Dry enough that it does not look or feel damp after you degrease it. An overnight wait is a rule of thumb, not a standard. If the corner is still dark in the morning, wait. Mould on the old bead is not the same as a wet wall, which is a reason to stop.
Which silicone goes around a bath, and what do I check on an acrylic bath?
Use a sanitary cartridge and read the class. Unibond cites type S and F-25LM. Bostik S31 cites XS2. On acrylic, read the tube. Soudal Stay Fresh is sold as acetoxy and as neutral, so the name is not the chemistry. Natural stone is excluded on several sanitary sheets.
How wide should the bead be?
illbruck’s practical fillet is about 4–5 mm on each face. Soudal’s 5 mm masking gap and Plumbing Superstore’s tape at least 3 mm off the wall are gun paths, not the same measurement. A very thin bead has almost no movement when the bath drops. A very wide bead cures slowly at about 2–3 mm per 24 hours.
How long does the water stay in the bath?
Until the cartridge has cured through, not merely skinned. About 2–3 mm per 24 hours is the figure used here, and Stay Fresh’s sheet is about 2 mm per 24 hours. Do not use the bath as a soak while that water is the weight. Do not empty it the same evening because the surface feels dry.
When should I stop and call someone?
Stop if the wall is wet, if the joint has failed twice, if the bath or screen is glass or a costly finish, or if you are stripping a whole room. Also stop if the only chemical to hand is an unknown solvent in a closed bathroom. A sanitary bead cannot seal a leak behind the panel.

Related pages

How to remove silicone sealant

Best silicone remover tool

Joint scraper

Silicone sealant tool kit: what to check before buying

Grout rake or silicone tool for the joint you have

Sources

Public UK sources listed below, last checked in October 2026. Shelf prices and star lines are the amazon.co.uk figures used on this page.

  1. Screwfix — How to remove silicone sealant (retrieved October 2026)
  2. Homebuilding — Specialist tool trial for silicone and caulk (retrieved October 2026)
  3. Bostik UK — S31 sanitary sealant technical data sheet (retrieved October 2026)
  4. illbruck UK — Wet rooms and bathrooms, the fillet (retrieved October 2026)
  5. HSE — DCM2, dichloromethane in bathrooms (retrieved October 2026)
  6. HSE — INDG463, silica dust and the workplace limit (retrieved October 2026)
  7. Soudal UK — Sealing around a bath (retrieved October 2026)
  8. legislation.gov.uk — Consumer Rights Act 2015, section 22 (retrieved October 2026)