Use this guide when sealant around your bath or shower is black with mould, peeling or cracked, or water is getting behind it. You will need a sealant remover tool or plastic scraper, a sharp blade, sanitary silicone, a sealant gun, masking tape and a smoothing tool.
Step by step
Remove the old sealant
Cut along the top and bottom edges of the old sealant with a sharp blade, taking care not to scratch the bath or tiles. Pull it away in strips and use a plastic scraper or removal tool for stubborn sections. Remove every trace, as new silicone will not bond well to old.
Clean and dry the joint
Clean the gap with a mould remover or bathroom cleaner, rinse, then wipe with methylated spirit or a surface prep product to remove soap residue. Leave the joint to dry completely, ideally overnight with the window open or a fan running. Silicone applied to a damp joint will fail early and trap mould.
Fill the bath first
Fill the bath with water before you seal it, and stand in the shower tray if that is safe. The weight makes the bath or tray drop slightly, so the sealant is applied at its widest gap. Leave the water in until the sealant has cured.
Mask and apply the silicone
Run masking tape along the tiles and the bath edge, leaving an even gap where the sealant will go. Cut the nozzle at 45 degrees slightly narrower than the gap, and apply a continuous bead in one steady movement along each side. Work on one side at a time.
Smooth and remove the tape
Smooth the bead straight away with a profiling tool or a finger dipped in soapy water, wiping off excess as you go. Peel the masking tape away at an angle while the silicone is still wet. Do not go back over areas that have started to skin.
Let it cure
Leave the silicone to cure for the time stated on the cartridge before using the bath or shower, usually at least a day. Keep the room ventilated. Drain the bath only once the sealant has fully set.
Ready-to-use checklist
- All old sealant removed
- Joint cleaned with mould remover and degreaser
- Joint completely dry
- Bath filled with water or tray weighted
- Masking tape applied with an even gap
- Sanitary grade silicone with mould inhibitor used
- Bead smoothed and tape removed while wet
- Curing time on the cartridge followed
Practical tips
- Practise running a bead on a piece of cardboard first to get a feel for the gun and your speed.
- Choose a sealant labelled for kitchens and bathrooms with a fungicide, not general-purpose or decorators' caulk.
- Keep a roll of kitchen paper and a bin bag within reach, because wet silicone gets everywhere quickly.
Common problems
The gap is wider than a pencil in places.
Push foam backer rod into wide gaps before sealing so the silicone has a firm base and does not sink. For very large gaps, consider a plastic bath trim or ask a tiler to check that the bath is properly supported.
Black mould has come back within weeks.
The joint was probably damp or dirty when sealed, or mould spores remained under the new bead. Remove the sealant, treat the area with mould remover, dry it thoroughly and reseal, and improve ventilation with an extractor fan.
The silicone has come out lumpy and uneven.
If it is still wet, wipe it off and start again on that section. If it has set, cut it out once cured and reapply, as layering new silicone over old rarely looks or seals well.