PURPOSE: To reduce the number of production processes to cut working cost and to perform natural patterning having streoscopic effect by blowing air onto a coating material curtain falling to shake it and forming a flow patterned coating consisting of a thick film part and a thin film part on a base coat.

CONSTITUTION: After the surface of a base plate consisting of a calcium silicate plate is subjected to sealer treatment with a damp cured urethane coating material, an acrylic urethane enamel coating material is applied by a curtain flow coater to form a base coat 2 of the same color as that of a natural stone to express. Next, curtain flow coating is applied on the base coat 2 by the curtain flow coater 3 and also air is blown from the side by an air nozzle 9 onto a coating material curtain 4 which flows down from a slit 8 between a pair of rolls 6, 7 in the bottom part of the curtain flow coater 3. By shaking the coating material curtain 4 by intermittent blowing, a flow patterned coating is formed on the base coat 2 on the base plate 1 transferred by a belt conveyor 17.