To produce a powdery or a granular material for retarding the hardening of a cement capable of simply and efficiently forming an aggregate exposed finish surface by washing on the surface of a concrete structure.

This powdery or granular material 2 for retarding the hardening of a cement comprises a powdery or a granular substrate and a covering material for covering the surface of the powdery or granular substrate. The covering material contains a component for retarding the hardening of the cement. A polymer, etc., capable of manifesting the ability to retard the hardening of the cement by hydrolysis can be used as the component for retarding the hardening of the cement. The polymer includes an unsaturated polyester, etc., prepared by reacting a polyvalent carboxylic acid component such as maleic acid with a polyol component such as ethylene glycol. The powdery or granular substrate includes a powdery or a granular metal, powdery or granular ceramics, an inorganic molding product, a resin molding product, etc. The powdery or granular material 2 for retarding the hardening of the cement is brought into contact with a surface of an inorganic hardenable composition 4 to carry out the hardening treatment of the inorganic hardenable composition 4. The powdery or granular material 2 for retarding the hardening of the cement and the unhardened inorganic hardenable composition 4 can be removed to thereby form an aggregate exposed finish surface by washing having a natural feeling on the surface of a concrete structure.