PURPOSE: To form a natural stone-like pattern abounding in variableness on the surface of a block building material by agitating and mixing other materials, previously adding and mixing glass fiber, adding a pigment and forming the irregular variable-density dispersed state of the pigment by the extent of agitation when glass fiber and the pigment are added to a mortar material.

CONSTITUTION: Mortar material powder is agitated and mixed. Water and a water reducing agent are added to the agitated and mixed mortar material powder, and agitated and kneaded. Glass fiber is added to the kneaded mortar material and mixed while a patterning pigment is added, and dispersed in avariable density. The kneaded material is injected into a molding die, pressed, solidified and cured, thus forming a natural stone-like pattern on the surface of a block building material.