Adhesives and glues are used to bond substrates like metal, glass, plastic, and wood in a wide range of sealing, joining, and attaching applications. Depending on the surface material and adhesive type, different methods are used to create bonds. These methods include air drying, heat drying, and chemical reaction. Drying adhesives include solvent-based adhesives like contact cements and construction adhesives. These types of adhesives harden as the solvent evaporates from the compound. Heat-activated adhesives include hot melts and some urethane adhesives. Reactive adhesives include methacrylate adhesives and epoxies. These adhesives are usually two-part systems where the bond forms through a chemical reaction once the two parts are mixed.
Sealants fill joints and gaps and are used to create air- or water-tight seals, offering environmental protection against dirt and corrosion. Sealants are also used as a component in firestopping. Sealants form a solid when cured, but retain some flexibility to maintain a tight seal when there is movement between parts.