PURPOSE: To achieve a cost reduction and to obtain high hardness by using a compsn. based on cement and containing lignosulfonate, lime, gypsum and silicate as auxiliary agents as a curing/coagulating agent curing and coagulating incineration ash in order to reutilize incineration ash as aggregate of a building material.

CONSTITUTION: As a curing/coagulating agent curing and coagulating the so- called fly ash being the fine powdery coal ash discharged from a steam power plant and the incineration ash discharged from a garbage incinerator in order to reutilize both of them as aggregate of a building material, a compsn. based on cement, containing lignosulfonate as a dispersing and fluidizing agent/water reducing agent and further containing lime/gypsum and silicate as a curing accelerating agent as auxiliary agents mixed with cement is used. This curing/ coagulating agent is mixed with incineration ash and the mixture of the curing/ coagulating agent and incineration ash are cured and coagulated to produce a desired building material. As silicate, aluminum silicate is pref. used. By this constitution, a building material having a high hardness is obtained at a low cost.