The pot life of an isocyanate formulation is controlled by including a chain extender having (a) at least two secondary amine groups, (b) no primary amine groups, and (c) a reactivity low enough that the chain extender will not react sufficiently with isocyanate groups present in the isocyanate formulation to increase the viscosity of the isocyanate formulation to more than 2000 mPa·s within 5 seconds in the isocyanate formulation.