Silicone joints are so-called movement or connection joints. Unlike rigid grout between tiles, silicone stays permanently elastic and absorbs the slight movement of a bathtub, shower tray or furniture. That is exactly why corner joints and connections at sanitary fixtures are always done with silicone rather than cement grout. In the bathroom, sanitary silicone with a fungicide is usually used to inhibit mould.
The joint is a wear part. Over time, moisture, cleaning agents and temperature changes make it brittle; it lifts at the edges or turns black from mould inside the material. It then no longer seals reliably and water can run behind the tub or tiles – a common but easily avoidable cause of moisture damage. As a rule of thumb, a sanitary silicone joint lasts around five to ten years before it should be renewed.
The renewal process: the old joint is fully cut out with a joint knife or silicone remover, the flanks are cleaned, degreased and dried. The tradesperson then masks the edges with painter's tape, applies fresh silicone evenly, smooths the joint with a spreader and removes the tape immediately. After curing – usually about 24 hours – the joint is fully serviceable again.
Renewing a single joint takes around half an hour to an hour depending on length and condition. As a guide, resealing a shower or bathtub costs roughly CHF 150 to 400, depending on call-out fee, joint length and the effort to remove the old joint (no guarantee). Many firms charge an hourly rate of around CHF 90 to 130 plus material.
What to watch for: the flanks must be clean and grease-free, otherwise the silicone won't hold. Never simply paint over an old joint – new silicone does not adhere to old. In the bathroom always use fungicidal sanitary silicone and occasionally wipe the joint dry after showering so mould cannot take hold.