PURPOSE: To enable to use calcium carbonate as an agent for improving the workability of various one pack type sealants such as for preventing the slumping thereof by treating the surface of calcium carbonate having a specified specific surface area with a fatty acid ester.

CONSTITUTION: The surface of calcium carbonate having a BET specific surface area of ≥3m2/g is treated with a fatty acid ester to provide the calcium carbonate for the moisture-curable one pack type sealant. When the BET specific surface area of the used calcium carbonate is smaller than the aforementioned value, the calcium carbonate can not give a thixotropic property to the sealant. Although especially not restricted, the fatty acid ester is preferably one composed from a ≥8C fatty acid and having an ester group of many carbon atoms. The addition of the calcium carbonate to a moisture-curable one pack type sealant permits to give good thixotropy, slump resistance and storage stability to the sealant.