Sealant fills gaps to prevent air or water passage. It is a flexible material that adheres to the surfaces and cures to form a seal. It is used around windows, doors, pipes, and joints. It is different from caulk, though the terms are often used interchangeably. Caulk is usually acrylic or latex and is paintable. Sealant is usually silicone, polyurethane, or butyl and is more durable and flexible. Sealant is used where movement is expected. Caulk is used where movement is minimal.

Sealants come in several chemistries. Silicone sealant is flexible, waterproof, and long-lasting. It is used in bathrooms, kitchens, and exteriors. Polyurethane sealant is strong and abrasion-resistant. It is used in concrete joints and automotive applications. Butyl sealant is sticky and permanent. It is used in roofing and gutters. Acrylic sealant is paintable and easy to clean up. It is used indoors. Each has its own adhesion, cure time, and movement capability. The choice depends on the substrate, the exposure, and the movement.

Sealant application requires preparation. The joint must be clean, dry, and free of old sealant. A backer rod may be inserted to control the depth and allow the sealant to move. The sealant is applied with a gun and tooled to a smooth bead. The bead must be concave to allow movement. A convex bead will peel. The sealant must cure before it is exposed to water. The cure time depends on the chemistry and the humidity. Sealant is a small part of the construction. It is a critical part of the envelope. A gap that is not sealed is a leak waiting to happen.