Mouldy Sealant Round The Bath

What's happening?

The bead round a bath is a movement joint. The bath moves as it fills and empties, the wall does not, and the silicone is what absorbs the difference. Mould grows in it because the surface stays wet, and once the growth is into the body of the silicone rather than on it, no cleaner reaches it — you are bleaching the surface of something that is stained all the way through. The other failure is mechanical: the bead lifts away from the tile or the bath rim on one edge, so water runs behind it and sits there permanently. Both are usually a symptom of the same two causes, a room that does not dry out and a bath that was sealed while empty and then filled.

What usually causes it?

• The bath sealed empty and then filled, so the first bath stretched the bead and tore it off one edge
• A bath or tray that moves more than the joint can take, because it is not fully supported underneath
• Sealant applied over a damp, dusty or soapy surface, so it never bonded
• The wrong product — decorator's or general-purpose silicone instead of a sanitary grade with a fungicide
• A new bead run straight over old, mouldy silicone, so the mould carries on growing under the new layer
• Poor ventilation, leaving the joint wet for hours after every use
• A joint too thin or too wide for the movement it has to absorb

When should you call a bathroom fitter?

Call a bathroom fitter if the seal has failed twice, if the bath or tray visibly moves when you stand in it, if the wall or floor beside the bath is soft, or if there is a stain on the ceiling below. Repeated seal failure is almost always movement, and the fix is under the bath, not in the joint. A bath that needs re-supporting, or tiling that finishes short of the rim, needs the sanitaryware taken out rather than another bead.

What will the bathroom fitter actually do?

• Strip the failed sealant out entirely and inspect the gap, the tile edge and the bath rim for water damage behind
• Check the bath or tray for movement and re-support or re-anchor it where it is not solid
• Correct the joint geometry where the gap is too wide, packing it properly rather than filling it with sealant
• Treat and dry any mould or damp in the void before resealing
• Reseal with a sanitary-grade silicone with the bath loaded, so the joint cures at its working width
• Check ventilation and report where the room's drying is the reason the last seal failed

Resealing a bath so it lasts

1. Cut the old bead out completely and remove every residue.
2. Clean the joint, treat any mould in the gap and let it dry fully.
3. Fill the bath with water to its normal level.
4. Run a single bead of sanitary-grade silicone and tool it once.
5. Leave the bath full and unused for the curing time on the tin, normally 24 hours.
6. Drain the bath only once the joint has cured.