A second mold is placed on a planar surface of a first mold to form a first mold cavity, which is filled with a first material slurry containing a first material powder and the molded slurry is caused to set, thereby forming a first molded part on the planar surface of the first mold. A third mold is placed on the planar surface of the first mold from which the second mold is removed and on which the first molded part is formed, thereby forming a second mold cavity. The second mold cavity is filled with a second material slurry which contains a second material powder different from the first material powder so as to mold the slurry in contact with the first molded part. The molded slurry is caused to set, thereby forming a second molded part on the planar surface of the first mold.