Catalyst

An organic peroxide used as the initiator, commonly called the catalyst, for curing unsaturated polyester and vinyl ester resins at room temperature. It is corrosive and a strong oxidiser, requiring careful handling, storage away from accelerators, and accurate dosing to control gel time.

An additive that speeds the cure of a resin or adhesive, allowing curing at lower temperatures or in shorter times. Cobalt salts are the usual accelerators for polyester resins, working in combination with the peroxide catalyst; pre-accelerated resins have the accelerator already blended in by the manufacturer.

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.

A chemical added in small amounts to a reactive resin to delay the onset of cure, extending shelf life and working time and protecting against premature gelation in storage or transport. Adjusting inhibitor level is one of the ways manufacturers tune the gel time of polyester and vinyl ester resins.

The time taken for a mixed resin to change from a workable liquid to a soft gel that can no longer be applied or moved. It marks the practical end of the working period and is quoted by resin suppliers at a stated temperature and catalyst addition.