Bathroom silicone sealant: when to redo it and what it cannot fix

The flexible bead between a bath or shower tray and the tiles has one job: to stop splashes and run-off getting into the gap behind. It has to stay flexible because baths and trays move slightly when they are filled and stood in. When the bead goes black, peels or splits, water can get behind it, and the damage that causes is far worse than the effort of redoing it.

Which sealant

Sanitary silicone is made for wet areas around baths, showers, basins and sinks. It usually contains a fungicide to slow mould growth and stays flexible once cured. This is the one for bathroom joints.

General purpose silicone may not have the mould resistance, and some types are intended for other jobs, such as glazing.

Decorators' caulk (acrylic) is for painted joints in dry areas. It is not designed for constant wetting and should not be used around a bath or tray.

Colour. White and clear are the usual choices. Clear shows mould and dirt underneath it more.

Check the tube for the surfaces it suits, especially for natural stone, which some silicones can stain.

When to redo it

• Black mould that is in the silicone, not just on the surface. Cleaning products will not reach it.
• Peeling, shrinking away from the tile or bath, or gaps you can push a fingernail into.
• Splits at the corners or along the long edge of a bath, where most movement happens.
• After any work that disturbs the bath, tray or tiles.

Removing the old sealant

New silicone does not stick well to old silicone, so all of it needs to come off.

1. Cut along both edges of the bead with a sharp blade or a sealant removal tool, keeping the blade flat to avoid scratching an acrylic bath or the tile glaze.
2. Pull the bead away in strips.
3. Remove the residue. A plastic scraper and a silicone remover product help with the thin film left behind. Follow the remover's instructions and ventilate the room.
4. Treat mould in the joint, rinse, and let it dry completely. Silicone will not bond to a damp or soapy surface. Leave it as long as you reasonably can, ideally overnight with the window open or the extractor running.

Applying new sealant

• Fill the bath first. A common tip is to part-fill the bath with water before sealing and leave it in until the silicone has cured, so the joint is sealed with the bath at its lowest. It is less likely to tear when the bath is used.
• Mask both edges with low-tack tape to get straight lines.
• Cut the nozzle to suit the gap, run a steady, continuous bead and smooth it with a profiling tool or a wetted finger, following the product instructions.
• Remove the tape straight away, before the silicone skins over.
• Leave it to cure for the time on the tube before using the bath or shower.

Keeping mould away

Fungicide in the silicone slows mould. It does not stop it in a room that stays damp. Run the extractor fan during and after showers, wipe the bead dry now and then, and leave the shower door open to let it dry. If mould returns within weeks, look at ventilation and at whether water is getting behind the joint.

What silicone cannot fix

Silicone seals the gap at the surface. It does not repair anything behind or under it:

• A leaking waste or trap under a bath or tray. See bath panels and traps and shower trays and wastes.
• A tray or bath that moves when you stand in it. The seal will keep splitting until the support is sorted.
• A leak from pipes in the wall, such as a shower valve connection.
• Failed grout or tanking inside a shower enclosure.
• A leaking toilet pan connector. See WC pan connectors.

If a stain on the ceiling below grows after you have resealed, the leak is somewhere else. Turn off the shower or bath, use the stopcock if you need to (see finding a leak and the stopcock), and call a plumber.

Sanitary silicone at Wickes

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

How often should bathroom silicone be replaced?

There is no fixed interval. Replace it when it is mouldy inside, peeling, split or shrinking from the edge. A well-ventilated bathroom with a stable bath will need it less often.

Can I put new silicone over old silicone?

It is not a good idea. New sealant does not bond well to old silicone, and any mould under it stays there. Remove the old bead completely first.

Why does my new silicone keep going mouldy?

Usually because the room stays damp, the joint was not fully dry when sealed, or water is getting behind the joint from a leak. Improve ventilation first. If it keeps happening quickly, ask a plumber to check for a leak.