How to reseal a bath or shower
Quick answer: Cut out and scrape off all the old sealant, clean and dry the gap thoroughly, fill the bath with water to open the gap, mask either side with tape, run a bead of sanitary silicone, smooth it with a damp finger or tool and pull the tape off straight away. Leave it 24 hours before using the shower.
Black, peeling sealant around a bath or shower tray lets water get behind the tiles and into the wall. Replacing it is a satisfying job and costs very little, but the old sealant has to be removed completely or the new will not stick.
The trick that makes the biggest difference is to fill the bath with water first, so the bath sits at its lowest point while you seal.
What you will need
- Sanitary (anti-mould) silicone sealant and a sealant gun
- A sealant remover or a sharp scraper, and a craft knife
- Masking tape
- Isopropyl alcohol or sealant-safe cleaner and clean cloths
- A sealant smoothing tool or a soapy finger
- Rubber gloves
- A bucket or a hose to fill the bath
Step by step
Remove the old sealant
Cut along the top and bottom edges with a craft knife, then peel and scrape out all of it. Use a sealant remover on stubborn residue and give it time to soften.
Clean the gap
Scrub the surfaces with isopropyl alcohol or a bathroom cleaner and rinse. Mould spores left behind will grow through the new sealant.
Dry it completely
Let it dry for several hours or use a hair dryer. Silicone will not stick to damp surfaces.
Fill the bath
Fill the bath nearly full with water, so it sits at its lowest and the gap is at its widest. For a shower tray, stand in it while you work, or put a weight in it.
Mask the edges
Put masking tape on the tiles and on the bath, leaving a gap of about 3 to 4 mm where the sealant will go. This gives you a straight edge.
Apply the sealant
Cut the nozzle at 45 degrees to a size matching the gap. Squeeze steadily and run one continuous bead along the joint, pushing it into the gap.
Smooth and remove the tape
Smooth the bead with a sealant tool or a finger dipped in soapy water. Peel off the masking tape straight away, pulling it away from the bead.
Let it cure
Leave it for the time on the tube, typically 24 hours, before running the water or using the shower. Then let the bath out slowly.
Tips
- Choose sealant labelled 'sanitary' with fungicide for bathrooms.
- Do not use decorators' caulk in wet areas. It is not waterproof enough.
- If the gap is wider than about 5 mm, use a flexible bath seal strip or backer rod first.
Stop and get help if
- The tiles or the wall around the bath are soft, crumbly or stained. Water may have got behind them.
- The bath or tray is moving or the gap is large. It may need refitting or support.
- You can see black mould that goes deep into the grout or plaster.
- You are not sure what the old sealant is. Some old products contain things you should not sand or inhale.
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Common questions
Why do you fill the bath before sealing?
A bath moves down slightly when full of water. If you seal when it is empty, the sealant can crack or peel away when you use the bath.
How long does sealant take to dry?
Most skin over in about 15 to 30 minutes and cure fully in 24 hours. Check the tube. Do not use the shower or bath until then.
Can I put new silicone over old?
No. It will not bond. Remove the old completely.
More guides
Last reviewed 17 October 2026. This guide is general information for UK homes and is not a substitute for the manufacturer's instructions. If the job involves gas, mains wiring, asbestos, structural work or working at height, or you are unsure, ask a suitably qualified person.