How to remove silicone sealant, and why nothing in the cupboard dissolves it

Start with the blade. Run it along the edge where the silicone meets the tiles, then along the edge where it meets the bath or tray, keeping it flat to each surface. Pull the strip out, then go back over the joint with a removal tool. Soudal's remover sheet opens with the same step: remove the cured sealant as much as possible using a sharp knife. UniBond's says the same about its gel.

What is left after that is a film. It is thin, it is stuck in the texture of the tile, and it is the part people give up on. This is where a solvent or a remover earns its keep, because a thin film swells through and lets go. A full bead only swells on the outside.

Owners who have tried both say the same thing. One put remover on whole beads and found it did nothing at all, not even softening them. Another explained why: people put it on full beads and expect them to come off, when the job is to cut away as much as you can and use the remover on the thin layer left.

If the bead was black with mould, the sealant makers want the mould gone as well before the new bead goes in, and why mould grows into silicone and keeps coming back is a page of its own. And if the seal had failed long enough for water to get behind it, the full reseal job, and what a failed bath seal does to the ceiling below, is worth reading before you buy anything.

The sealant makers do not leave room for argument here. UniBond's bathroom sealant sheet says residues of old sealant, and mould, must be removed completely, and that surfaces must be clean and dry, free from dust and grease. Its how-to says the new sealant won't adhere unless the surface is clean and dry.

There is one product sold to go over old sealant, a coating called Re-New. Its own data sheet says a working, waterproof seal must already be in place before you use it, and that it will not provide a seal on its own. So it can freshen a seal that still works. It cannot fix one that leaks.

Three things sabotage a clean joint after all that scraping. Remover left on the surface, which is why UniBond says to wipe the area clean and then go over it with methylated spirit before resealing. The oily film from WD-40, which its maker says must be completely removed. And soap: Soudal's sanitary silicone sheet says that if a soapy finishing solution touches the surface, the sealant will not stick to it. Don't wash the joint down with washing-up liquid as the last step.

Then check it with your fingers. It should feel smooth, with no remnants of the old sealant. Give it time to dry properly too, because a wet joint is no better than a dirty one, and how long the new silicone needs before the shower goes back on is the next question you will have. The bead itself, the tape and the smoothing are all on how to apply silicone sealant neatly.

One last reason to do it properly. A seal that lets water past at the back of a bath or shower tray sends it somewhere you can't see, and a mark on the ceiling under a bathroom is one place it can show. It is the same rule as anywhere else on this site: water getting in has a location, and a gap in a bead of silicone is a location. If you would rather not do the job yourself, what it costs to have a bath resealed is on its own page.