sealant

Sealant is a viscoelastic material used to seal joints and cracks, blocking the passage of liquids or gases and accommodating movement between adhered surfaces. It is applied as a paste or extrudable compound and cures in place to form a flexible or rigid seal that remains bonded over time. Sealants differ from caulks in being designed to resist environmental exposure and to accommodate substrate movement.

Common sealant families include silicone, polyurethane, polysulfide, acrylic, and epoxy. Silicone sealants are highly elastic and weather-resistant, widely used in glazing, bathrooms, and exterior joints. Polyurethane sealants offer strong adhesion and good chemical resistance, suitable for structural joints, concrete, and expansion joints. Polysulfide sealants provide chemical resistance and durability for aerospace, industrial, or fuel-resistant applications. Acrylic sealants are easy to apply and paintable, often used indoors where movement is limited. Epoxy sealants are rigid and very strong, used for metal and concrete joints where minimal movement is expected.

Curing mechanisms vary: many silicones cure by moisture in the air, while polyurethanes may cure by moisture or solvent evaporation. Epoxies cure chemically, and some hot-melt sealants set with heat. Selection depends on substrate, expected movement, exposure to water or chemicals, temperature range, and whether the sealant must be paintable.

Applications span building construction (joints between panels, windows, doors), glazing, plumbing, automotive, electronics, and industrial equipment. Proper surface preparation and adhesion testing improve performance and longevity.