How to reseal a bath
Black mould in the sealant, a bead that’s peeling away, or a gap you can slide a fingernail into. Resealing a bath is one of the best-value DIY jobs in the house, as long as you take the prep seriously.
Guide · The Honest Fix
A good first job. The prep matters more than the bead.
Tools and materials
- Sanitary silicone with fungicide (white or clear)
- Sealant gun
- Silicone remover gel or a dedicated sealant removal tool
- Plastic scraper and a sharp blade (used carefully)
- Isopropyl alcohol or white spirit, and lint-free cloths
- Low-tack masking tape
- Profiling tool, or a spray bottle of soapy water for your finger
- Mould remover, if there’s mould under the old sealant
What the job is and when you need it
The sealant between your bath and the wall keeps water out of the gap, off the wall behind and away from the floor below. Once it peels, splits or grows mould you can’t clean off, water gets behind it. That leads to stained ceilings downstairs, rotten floor timbers and loose tiles.
Expect to redo it every few years. If it fails within months, something else is going on, usually a bath that moves when it’s filled. More on that below.
Step by step
1. Strip out the old sealant
Cut along both edges of the old bead with a sharp blade, holding it flat to avoid scratching the bath or tiles. Pull the bead out in strips. On an acrylic bath, use a plastic scraper rather than a metal blade.
Thin smears left behind won’t come off with scraping alone. Apply silicone remover gel, leave it for the time on the tube, then scrape and wipe. New silicone will not stick to old silicone, so every trace has to go.
2. Deal with any mould and let it dry
If there’s mould in the joint, treat it with a mould remover and rinse. Then leave the joint to dry fully, ideally overnight with the window open or the extractor on. Sealing over damp is the main reason new sealant fails early.
3. Clean and degrease
Wipe both surfaces with isopropyl alcohol or white spirit on a clean cloth to remove soap film and grease. Don’t touch the joint with your fingers afterwards.
4. Fill the bath with water
Fill the bath most of the way with cold water before you seal. A full bath sits lower, especially an acrylic one, so you seal it in its loaded position. If you seal it empty, the bead gets stretched the first time someone gets in.
5. Mask the joint
Run low-tack masking tape along the tiles and along the bath edge, leaving a gap the width you want your bead (usually 6–8mm). It’s the easiest way to get clean, straight lines.
6. Apply the silicone
Cut the nozzle at 45 degrees, a little smaller than the gap. Push the bead ahead of the nozzle in one steady run per side, rather than dragging it behind. Keep the pressure even and don’t stop halfway along if you can help it.
7. Tool it off and remove the tape
Lightly mist the bead with soapy water, then run a profiling tool or a wet finger along it in one pass. Wipe off excess as you go. Pull the tape away at an angle straight away, before the silicone skins.
8. Leave it to cure
Leave the water in the bath and don’t use it until the silicone has cured. Most sanitary silicones need around 24 hours, but check the cartridge for the product you’re using. Then drain the bath.
Safety
- Silicone removers and white spirit give off fumes. Open a window and keep the extractor running.
- Cut away from yourself and keep the blade flat. Old enamel chips easily and acrylic scratches.
- If the bath is near an electric shower or shaver socket, keep water and solvents away from them.
Stop here: call a pro if…
- There’s a stain on the ceiling below, or the floor around the bath feels soft or spongy.
- The bath moves, rocks or drops noticeably when you stand in it. It needs its legs or cradle adjusting and possibly extra support first.
- Tiles are loose, cracked or hollow-sounding behind the joint, or the wall behind is soft.
- The gap is wider than about 10mm, or very uneven. It probably needs a trim, backing rod or the bath refitting.
- New sealant splits again within a few months.
DIY or Hire?
DIY, for most people. Materials cost around the price of a takeaway, and the skill is mostly patience. Your first bead may not be perfect, but it can be cut out and redone.
It’s worth getting someone in if the bath moves, if there are signs of a leak, or if the joint is behind a tricky shower screen and you only want to do it once. A pro will also spot a bath that isn’t properly supported, which is the root cause behind many failed seals.
Common mistakes
- Sealing over old silicone. It won’t bond and will peel within weeks.
- Sealing onto a joint that’s still damp underneath.
- Sealing with the bath empty, so the bead tears when the bath is used.
- Using decorators’ caulk or general-purpose sealant instead of sanitary silicone with fungicide.
- Laying too fat a bead and smearing it trying to tidy it up.
- Using the bath before the silicone has cured.
FAQs
Can I put new silicone over the old?
No. Silicone doesn’t stick to silicone, and you’ll be sealing in any mould. Strip it all out.
White or clear silicone?
White matches most baths and hides small imperfections. Clear shows any mould or dirt underneath, so prep has to be spotless.
Should I use sealant strip instead?
Self-adhesive strips are quick but tend to lift on uneven tiles and in steamy bathrooms. A properly laid silicone bead lasts longer.