Mastic sealant — the silicone sealant that seals the joints between the bath and tiles, the shower tray and tiles, and the floor and wall tiles — is one of the most important but most overlooked elements of bathroom maintenance.

When to Replace Bathroom Mastic

Black mould — black discolouration in sealant is mould growing within the silicone. It cannot be cleaned out — the sealant must be removed and replaced.
Cracking and shrinkage — old sealant cracks and shrinks away from the surfaces it was sealing, allowing water to penetrate behind tiles and under bath rims.
Peeling or lifting — where the sealant has lost adhesion to the tile or bath surface.
Discolouration — yellowing or browning of white sealant from age and cleaning products.

The Mastic Replacement Process

The existing sealant is removed completely using a Stanley knife and sealant remover tool. Surfaces are cleaned and dried thoroughly. New silicone sealant is applied in a single continuous bead and tooled smooth.

Good mastic application is a skill — a poorly applied sealant bead looks untidy and fails faster than a professionally applied one.

How Often Should Mastic Be Replaced?

In a regularly used bathroom, mastic should be inspected annually and replaced every 5-10 years as a preventive measure — or immediately when mould, cracking or lifting is observed.