Exotherm

The length of time a mixed, reactive resin or adhesive remains usable in the mixing vessel before it thickens beyond application. Pot life shortens as temperature and mixed quantity increase, because the curing reaction generates its own heat.

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.

The chemical process by which a liquid resin or adhesive hardens into its final solid state through crosslinking, driven by a hardener, catalyst, heat, moisture or radiation depending on the chemistry. Full properties develop only when cure is complete, which can take considerably longer than the initial set.

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.

The programmed schedule of temperature, pressure and vacuum against time under which a thermosetting laminate or adhesive is cured, including heating ramps, dwells and cool-down. The cycle is defined in the material's processing data and qualified for the specific part and process.

The removal of dissolved and entrained air from mixed liquid resin, usually by holding it under vacuum until bubbling subsides, before infusion or casting. Degassing reduces void formation and is particularly important for clear castings and high-performance infusions.