To provide mineral-base clay having water resistance and strength enhanced by heating at a low temperature which can be easily heated at a low temperature of 100-180°C by using a commercially available microwave oven or toaster oven and to which water resistance is added and whose strength is made excellent by the heating.

This clay is obtained by kneading the composition consisting of natural mineral product clay, acrylic copolymer emulsion, a pasting agent, filler for preventing shrinkage, fibrous powder and water. The minimum film- forming temperature(MFT) of the acrylic copolymer emulsion is 30-100°C. The kneaded composition is dried naturally at ambient temperature. The dried compact is heated at a low temperature of 100-180°C to extremely enhance the water resistance and strength.