To obtain the subject composition suitable for a waterproof material, etc., by mixing a component containing an isocyanate group terminal prepolymer obtained by reacting a high-molecular weight polyoxyalkylene polyol having a low total unsaturation degree with an excessive polyisocyanate with a component consisting essentially of calcium carbonate and curing the mixture with water in atmosphere, etc.

This composition is obtained by mixing (A) a component which is prepared by reacting a polyoxyalkylene polyol having ≥2,000 molecular weight per hydroxyl group and ≤0.07 meq/g total unsaturation degree with an excessive polyisocyanate (e.g. tolylene diisocyanate) and comprises an isocyanate group terminal prepolymer containing preferably ≤2 wt.% of isocyanate group with (B) a substantially powdery component consisting essentially of calcium carbonate and reacting and curing the mixture with water contained in atmosphere and/or in the component B. The mixing ratio of the component A to the component B is preferably 1/0.2 to 2.0.