A method of controlled curing by a metathesis reaction upon mixing its components, the method including the step of mixing an olefin-containing substrate, a metathesis catalyst, and a reaction control agent. The metathesis catalyst is a ruthenium or osmium carbene complex catalyst, such as one containing an alkylidene ligand with basicity higher than that of tricyclohexylphosphine (PCy.sub.3) and a neutral electron donor ligand with a basicity lower than that of PCy.sub.3, whereby the catalyst initiates the metathesis reaction of the composition upon mixing with the substrate. The reaction control agent is effective to slow the progress of the metathesis reaction and prevent its completion in the absence of an elevated temperature. The control agent may be a hydrocarbon containing carbon-carbon double bonds and/or triple bonds, or maybe a modified hydrocarbon with one or more Group 14 or 15 atoms. Prior to catalyst deactivation, the mixture is exposed to an elevated temperature to accelerate the catalyst and allow the metathesis reaction to proceed toward completion.