Elastomer composites are prepared by wetting particles of a natural or synthetic rubber with a liquid one-component moisture-curable resin composition and then exposing the wetted particles to moisture to cure the resin composition. The moisture-curable resin composition comprises (a) an isocyanate-terminated polyurethane prepolymer having an isocyanate content of from 0.5 to 12% by weight and (b) from 1 to 30%, based on the combined weight of components (a) and (b), of an epoxide or lactone compound having a molecular weight of from about 70 to about 1000 and which is miscible in the prepolymer at the relative proportions thereof that are present. In addition, the composition contains no more than 0.1% by weight of compounds having a primary or secondary amino group.