PURPOSE: To improve commercial value by forming a cement lower layer on the surface of a formed lightweight concrete and a synthetic-resin upper layer thereon and then applying a synthetic-resin emulsion contg. pigment to form a patterned layer.

CONSTITUTION: A formed article 1 of specified shape is formed from a lightweight concrete, a cement coating material such as cement mortar is applied on the surface in about 1mm thickness to form a lower layer 2, hence the pores generated on the formed article 1 surface are closed, and the surface is smoothed. A discoid coating controller 3 of sponge having a specified diameter is fixed at the center. An elastic and waterproof synthetic-resin coating material is applied on the surface of the lower layer 2 except on the controller 3 to form an upper layer 4 having about 1mm thickness. A synthetic-resin emulsion contg. pigment is applied on the upper layer 4 surface except on the controller 3 to form a patterened layer 5, then a transparent acrylic silicone resin coating material is applied to form a topcoat 6, and the controller 3 is removed to obtain a patterened panel product.