Methyl ethyl ketone peroxideMEKP

A substance that initiates or speeds a resin's curing reaction without being consumed in stoichiometric amounts. In the GRP trade the organic peroxide added to polyester resin, usually MEKP, is called the catalyst, although strictly it acts as an initiator.

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.

A thermosetting resin dissolved in a reactive monomer, usually styrene, that cures by free-radical polymerisation when initiated with an organic peroxide such as MEKP. It is the workhorse matrix for glass-reinforced plastic in boat building, GRP roofing, tanks and vehicle panels, offering low cost and straightforward processing.

A thermosetting resin made by reacting an epoxy resin with an unsaturated acid and dissolving the product in styrene; it processes like a polyester but offers better toughness, chemical resistance and resistance to hydrolysis. Commonly specified for boat hulls, chemical plant, tank linings and as a barrier layer against osmosis.

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.