To provide a coating composition for a sealer excellent in frost damage resistance, water permeation resistance of a coating film thereof and coating film strength, and an inorganic building material coated with the coating composition for a sealer.

The coating composition for a sealer contains a resin emulsion containing emulsion particles having a glass transition temperature of -70 to 10°C, a pigment and a rheology control agent, wherein the amount of the pigment per 100 pts.wt. nonvolatile matter in the resin emulsion is 185-900 pts.wt. and the effective ingredient amount of the rheology control agent is 0.01-5 pts.wt.