SEALING IN THE BATHROOM

In a bathroom, shower or around a kitchen sink use a silicone intended for sanitary and damp rooms. Sanitary silicones are formulated for high-humidity environments and normally contain protection against mould growth.

Typical applications are:

• bath to tiles
• around a shower tray
• internal corners of the tiling
• around sinks and basins
• between worktop and splashback
• on certain sanitaryware
• other connections regularly exposed to water

Do not apply new silicone over the old one, especially if the old joint is:

• blackened
• cracked
• debonded
• covered in mould
• no longer elastic

Cut the old silicone out with a knife or a dedicated tool and remove the residues from both faces. The new silicone must bond to the clean substrate, not to remains of the old sealant.

Pay particular attention to residues of:

• soap
• shampoo
• cleaning agents
• grease
• limescale
• old silicone

They can be almost invisible on the tiles and still reduce adhesion significantly.

On suitable non-porous surfaces use a degreaser recommended by the manufacturer or a suitable alcohol-based cleaner.

This matters most when refurbishing an old bathroom. Once you remove the silicone around a bath or shower, trapped moisture may sit behind it.

Do not close a wet joint with fresh silicone. Let the area dry out fully. If needed, leave the shower or bath unused long enough before the work so no residual water remains in the joint zone.

Acrylic and some plastic baths shift slightly when filled with water and when someone steps in. If you seal an empty bath and then load it, the gap between bath and wall can widen and stretch the finished joint on first use.

For an acrylic or plastic bath, where both the bath and sealant manufacturers allow it: fill the bath about half with water before sealing and keep it loaded for the time stated in the sealant instructions. The joint then forms closer to its real working position.

For heavy steel, cast iron or otherwise rigidly fixed sanitaryware the rule does not apply in the same way.

A huge amount of silicone is not the point. What matters is continuous contact with both faces along the whole length of the joint.

Silicone can feel dry on the outside fairly quickly, which does not mean it is cured through. Curing progresses from the surface inwards.

For sanitary silicones a typical rate is around 2–3 mm per 24 hours at about 23 °C and 50% relative humidity, but it varies with product, temperature, humidity and joint size.

One rule applies to tiling: wherever two planes can move relative to each other, an elastic joint is required. Typical places are:

• wall to wall
• wall to floor
• tiles to bath
• tiles to shower tray
• worktop to wall

Rigid cementitious grout struggles to absorb movement between these elements and can crack. Such connections are therefore normally made with a suitable elastic sanitary sealant.