Decorative precast concrete boards and process for producing the same

摘要: Decorative precast concrete boards having a pore-free decorative porcelain-tile-like, hewn-stone-like or relief surface and porous core layer are provided. Such produced by applying inorganic cement mortar containing siliceous volcanic sand called "shirasu" in flat mold made of an elastomeric material so as to form the pouring thereon expanded particles said aggregate. The do not suffer efflorescence.