If the mould sits only in the sealant, a proper reseal fixes it. That means cutting out every trace of the old silicone, cleaning and drying the joint thoroughly, and applying fresh sanitary sealant. Wiping bleach over mouldy silicone rarely works for long because the growth lives inside the sealant, not on it. If the tiles are loose, the grout is crumbling or there are stains on the ceiling below, the sealant is a symptom, and the bathroom needs a closer look.
Why mould grows in sealant
Silicone sits in the wettest, least ventilated corner of the room. Soap residue and body oils give mould something to feed on, and a joint that never fully dries between showers gives it the damp it needs. Once the spores are inside the sealant, surface cleaning only lightens the colour for a while.
Poor ventilation makes every one of those factors worse. A bathroom without a working extractor fan, or one where the fan is switched off because it is noisy, will grow mould on fresh sealant within months.
How a proper reseal is done
The difference between a reseal that lasts and one that fails is almost entirely preparation.
- Cut out all old sealant, including thin traces left in the corners
- Clean the joint and treat any remaining mould spores
- Let the joint dry out completely, which can take longer than people expect
- Fill a bath with water before sealing so the joint is set at its widest
- Apply a sanitary grade sealant in one smooth, continuous bead
- Leave the shower unused until the sealant has fully cured
Signs it is more than a sealant problem
Mould that returns quickly after a careful reseal is a clue in itself. Water may be getting behind the tiles or the tray and wicking back out through the joint. Press gently on tiles around the shower; any movement or a hollow sound suggests the adhesive behind has let go.
Downstairs, look for staining or bubbling paint on the ceiling under the bathroom. In the room itself, a soft or springy floor near the bath or shower, crumbling grout lines or a musty smell that never clears all point to water where it should not be.
Reseal, regrout or refit
A sound bathroom with tired silicone needs a reseal and nothing more. A bathroom with good tiles but failing grout can often be refreshed by raking out and regrouting the worst areas at the same time. Where tiles are loose, the tray has moved or water has damaged the wall or floor behind, patching tends to be a false economy, and a planned refit with proper waterproofing behind the tiles is the lasting answer.
If you are already thinking about a new bathroom in the next year or two, it is still worth resealing now. It protects the structure while you plan, and it costs little compared with repairing rot.
Grout, tiles and the joint between them
Sealant and grout do different jobs. Grout fills the narrow gaps between tiles and is rigid, while sealant goes wherever two surfaces meet and may move against each other: the bath and the wall, the tray and the tiles, the corners of the room. Using grout where sealant belongs is a common cause of cracking, because a bath flexes slightly every time it is filled and a rigid joint simply splits.
It is also worth checking the grout along the lowest rows of tiles when the sealant is cut out. If it is soft, dark or missing, water has probably been sitting in the joint for a while, and raking out and regrouting that strip before resealing gives the new bead a sound, dry edge to stick to.
Keeping new sealant clean
Run the extractor during showers and for a while afterwards, leave the shower door or curtain open to let the tray dry, and wipe the joint down now and then. None of this is complicated, and together it keeps a well laid bead clean for far longer. Cracked or peeling sealant should be dealt with promptly, because it lets water straight into the joint behind.