What you need
- A sharp blade or sealant removal tool and silicone remover
- Isopropyl alcohol or a suitable cleaner, and lint-free cloths
- Mould-resistant sanitary silicone and a sealant gun
- Masking tape and a smoothing tool
Step by step
- Cut out all of the old sealant, then remove the residue. New silicone won’t stick to old.
- Clean the joint, treat any mould and let it dry completely.
- Fill the bath with water. This lowers it to its heaviest position, so the joint is at its widest.
- Mask a neat line either side of the joint.
- Apply a continuous bead, smooth it with the tool, then peel off the tape straight away.
- Leave the water in and let the sealant cure, usually around 24 hours, before draining and using the bath.
Common mistakes
- Sealing over old silicone
- Sealing a damp joint
- Sealing an empty bath, so the bead tears when the bath is first filled
- Missing the awkward bits behind the taps
Choosing the right sealant
Use a sanitary silicone made for baths and showers, ideally labelled as mould-resistant. Decorators’ caulk and general-purpose acrylic sealants aren’t suitable for joints that stay wet. Choose white or clear to match the bath and tiles; clear shows dirt and mould behind it less obviously when new, but white usually looks neater against a white bath. Check the date on the tube, because old silicone may not cure properly.
Removing old silicone completely
This is the step most DIY reseals skip, and it’s the main reason new silicone peels. Cut along both edges of the old bead with a sharp blade held flat, pull it out, then remove the thin film left behind with a plastic scraper and a silicone remover. Wipe the joint with isopropyl alcohol so no residue is left. If there’s mould in the grout or under the old silicone, treat it with a mould remover and let the joint dry fully, ideally overnight.
Getting a neat bead
- Cut the nozzle at an angle to suit the gap, starting small; you can always cut more off.
- Push the gun along the joint rather than dragging it, so the silicone is forced into the gap.
- Work in one continuous run along each side if you can, so there are fewer joins.
- Smooth with a profiling tool or a gloved finger dipped in soapy water, wiping excess off as you go.
- Peel the masking tape off straight away, pulling away from the bead, before the silicone skins over.
Wide or uneven gaps
If the gap between the bath and the wall is wider than about the width of a pencil, silicone alone is likely to sag or split. Push a foam backing rod into the gap first, so the silicone has something to sit on, or use a bath sealing strip for very wide gaps. If the gap keeps getting wider, the bath may be moving, which needs fixing first; acrylic baths in particular need firm support.
How long a reseal lasts
A well-applied reseal should last a long time, but in a bathroom it will eventually discolour or let mould grow behind it, especially if the room isn’t well ventilated. Signs it needs doing again include black spots that won’t clean off, gaps or lifting at the edges, and water getting behind the bead. Read black mould in bath sealant.
Keeping new sealant clean
- Ventilate the bathroom during and after showers, with an extractor fan or open window.
- Wipe water off the sealant after use where you can.
- Clean it gently with a mild bathroom cleaner; avoid scraping it with anything sharp.
- Don’t leave shampoo bottles sitting along the joint.
Resealing a shower tray or basin
The same method works for shower trays, basins and kitchen worktops. For a shower tray, stand in it while the sealant is applied if you can, or put weight on it, for the same reason you fill a bath: it opens the joint to its widest. Around a shower screen, seal the outside of the screen rather than the inside, so water that gets past the screen can drain back into the tray. For basins and worktops, make sure the surface is completely dry, as these joints often stay damp from splashes.
When resealing won’t fix the problem
If sealant keeps splitting within weeks, something is moving. Common causes are an acrylic bath without enough support, a shower tray that flexes, or a stud wall that moves. Resealing again won’t cure it until the movement is fixed. Water staining below a bath or tray, or tiles that sound hollow, can also mean water has been getting behind the seal for some time. In those cases, it’s worth having the bath or tray checked before resealing.
Or let us do it
Our resealing service removes the old mastic completely and reseals baths, showers and sinks, including behind the taps.
Quick answers
Can I put new silicone over old?
No. New silicone doesn’t bond to old silicone, so it peels and lets water behind.
How long before I can use the bath?
Leave it as long as the sealant’s instructions say, usually around 24 hours.
Do you reseal on the same visit as a repair?
Yes. We often repair a chip and reseal the bath on one visit, so you only have one day without it.
What does professional resealing cost?
It depends on how many joints and how long they are; we give a fixed price with your quote.
Every job is different. Send us a photo and we’ll tell you what we’d recommend for your bath, sink or surface.
