Silicone sealant

Silicone sealant is usually a one-part paste that reacts with moisture in the air and becomes a rubbery silicone. Acetoxy grades smell of vinegar while curing. Neutral-cure grades use different crosslinkers and are usually the safer choice around metals, mirrors and alkaline masonry. Cure starts at the exposed surface and moves inward, commonly only a few millimetres per day. A deep plug may skin over while remaining soft inside. Use a joint depth that matches the maker's design guidance rather than filling a large void solid. Silicone is chosen for movement, weather and water sealing, not because it is a high-strength general adhesive. It stays elastic and handles ultraviolet light well, so it suits sanitary joints, glazing and external seals. It is a poor base for paint, and fresh silicone adheres badly to cured silicone. Remove the old bead rather than laying another one over it. Adhesion varies sharply with formulation and substrate. Glass, glazed ceramic and clean metal are usually straightforward. Porous stone, some plastics, bituminous materials and powder coatings may need a primer or a different sealant. High-temperature, aquarium, food-area and potable-water grades are separate products with separate approvals. Do not assume a bathroom tube has any of those certifications.

Sealing baths, showers, sinks and worktops; glazing and window perimeter joints; flexible weather seals; sealing around non-porous sanitary fittings; low-load bonding where movement matters more than stiffness.

Cut out all old sealant. Remove residue rather than smearing it thinner. Clean soap, grease and dust, then let the joint dry. Mask the edges before gunning. Use backing rod to control depth in wide joints and avoid three-sided adhesion. Test plastics, coated metals and stone. Use the primer named by the sealant maker where one is specified.