Isocyanate

A broad polymer family formed by reacting isocyanates with polyols, producing everything from soft foams and elastomers to rigid plastics, adhesives, sealants and coatings. In construction and roofing it appears as insulation foam, liquid-applied waterproofing membranes and flexible adhesives, and many one-part grades cure with ambient moisture.

A curing mechanism in which a one-part adhesive, sealant or coating reacts with atmospheric humidity, hardening from the exposed surface inwards. One-part polyurethanes, silicones and silane-modified polymers cure this way; cure through thick sections is slow and depends on humidity and temperature.

The component of a two-part resin or adhesive system that reacts chemically with the base resin to build the cured polymer network. Unlike a catalyst it is consumed in the reaction and must be dosed at the manufacturer's stated mix ratio; amines and anhydrides are common hardeners for epoxies.