Mastics for Weatherproofing and Joint Sealing

Mastic sealants are formulated to seal joints and gaps against water, air and dust. They remain flexible to accommodate movement and are commonly used around windows, doors, baths and exterior cladding.

Applications and product types

There are silicone mastics for wet areas and high elasticity, polyurethane mastics for strong adhesion and paintable acrylic mastics for interior finishing. Choose the right mastic depending on exposure, substrate and whether painting over is required.

How to choose and use mastic

• Flexibility and movement: select a mastic with suitable elongation for joints that expand and contract.
• Paintability: some mastics accept paint; others, like neutral-cure silicones, are not paintable.
• Surface prep and tooling: clean and dry joints, apply with a cartridge gun and tool smooth for a neat finish.

Mastic sealants come in cartridges and tubes for easy application. For larger projects, compare trade sizes and look out for promotional deals to reduce costs. Follow curing times and manufacturer instructions, especially in cold or damp conditions where cure can be slower. Correctly applied mastic keeps buildings weathertight and improves energy efficiency by sealing air leaks and preventing moisture ingress.