How do I reseal a bath?

Two things make a resealing job fail. New silicone will not bond to old silicone, so any residue guarantees a leak. And a bath sags several millimetres when full of water and a person — sealing an empty bath means the joint stretches and splits the first time it's used.

Safety

What you'll need

• Sanitary (mould-resistant) silicone and a cartridge gun
• Sealant removal tool or sharp knife
• Silicone remover solvent
• Masking tape
• Isopropyl alcohol or methylated spirit
• Cloths and a smoothing tool

Step by step

1. Cut out the old sealant along both edges and lift it away in strips.Work along the joint rather than picking at it. Long strips come out cleanly; picking leaves fragments.
2. Remove every remaining trace with a solvent silicone remover and a plastic scraper.New silicone will not stick to old silicone. This step is the whole job — do not rush it.
3. Clean the joint with isopropyl alcohol and let it dry completely.Any moisture, soap film or dust in the joint becomes a failure point.
4. Fill the bath with water before sealing.A full bath sits several millimetres lower. Sealing empty means the bead tears the first time someone uses it.
5. Mask both sides of the joint, leaving the gap you want the bead to be.This is what gives a straight professional line, and it takes ten minutes.
6. Cut the nozzle at 45° to slightly under the joint width and apply one continuous bead.Steady, even pressure and constant speed. Stopping and restarting shows.
7. Tool the bead smooth in one pass with a wetted finger or smoothing tool, then pull the tape off immediately.Immediately — while the silicone is still wet. Waiting drags the bead.
8. Leave it to cure per the tube — usually 24 hours — before draining the bath.Draining early puts the joint under stress before it has strength.

Tips

• Use sanitary-grade silicone with a mould inhibitor. Standard silicone in a wet area grows black spots within a year.
• A drop of washing-up liquid in water makes a good tooling solution — it stops the silicone sticking to your finger.
• Cut the nozzle smaller than you think. You can always widen it; you cannot make the bead thinner once it's out.
• Warm the cartridge in a bowl of warm water first in cold weather. Cold silicone is very hard to extrude smoothly.

Common mistakes

• Sealing over old silicone — It will not bond. The joint fails within weeks and you do the whole thing again.
• Sealing an empty bath — The bath drops when filled and the new bead splits immediately.
• Leaving masking tape until the silicone skins — Pulling it then tears a ragged edge into the bead.
• Using general-purpose rather than sanitary silicone — No mould inhibitor means black spotting within a year in a wet room.

Questions people ask