Which sealant to use in the bathroom (and which not to)

The map of the room

On meetings that see water — shower corner, tray, bath, basin — I want sanitary silicone: elastic, water-shedding, with fungicides. Tile moves a little; acrylic moves more. A stiff sealant opens.

On dry meetings you will paint — ceiling, a door lining, sometimes skirting out of splash — acrylic sealant. It is water-based, it takes paint, and it is not meant to sit in a puddle.

Hybrid or MS: when you need to paint a meeting outside the wet zone, or a very specific substrate. It is not the shower shortcut. Silicone does not bond on moisture; hybrid sometimes will, but “a bit damp” on a tray is still a bad idea. Dry first.

Stone and the cheap cartridge

Marble, granite, agglomerate: natural-stone silicone, without plasticisers that stain the edge. Ordinary shower sanitary is not that chemistry.

The cheap cartridge is often full of fillers. They evaporate, the bead shrinks, it pulls the flanks and leaves hairline cracks. Fungicides fade early. On ceramic I use OTTOSEAL S100; on stone, the stone line. I want it to stretch and come back.

How to apply it (colour is the easy bit)

Old silicone out, film included. Technical degrease, not glass cleaner. In deep joints, PE backer rod so you do not bond on three faces. Primer if the substrate needs it — acrylic tray rims, often. Push the mass in; tool with a neutral liquid.

Acetoxy or neutral

Acetoxy smells of vinegar and, on glazed tile, holds up well. It can attack aluminium and some plastics. Neutral is kinder to metals and acrylic. In a mixed bathroom I choose by meeting, not “one tube for the lot”.

Mistakes

Acrylic in the shower: it softens or washes out. Silicone over old residue: it will not grab. Washing-up liquid when tooling: goodbye fungicides. Paint on silicone: paint will not stick; if it has to be painted, it was not silicone.

Exceptions

Substrate still damp: wait. Primer only where it is needed — well-degreased glass and ceramic often do not. Typical cure: around 2 mm a day; a shower joint often wants 24–48 hours before water load, longer if it is thick.