Abstract: A water-soluble inorganic composition obtained by reacting an inorganic dissolution promoter with at least one solute selected from the group consisting of metal silicon, boric acid, and borax at a ratio of the inorganic dissolution promoter to the solute of 1:10 to 1:100 by weight, wherein the inorganic dissolution promoter is obtained by mixing in water (A) at least one compound selected from the group consisting of an alkali metal fluoride, an alkali metal phosphite, an alkali metal sulfite, an Alkali metal nitrite, sulfurous acid, nitrous acid, and phosphorous acid, alkali metal phosphate, alkali metal nitrate, alkali metal sulfate, phosphoric acid, nitric acid, sulfuric acid and (B) at least one alkali metal hydroxide at a ratio of (A):(B) of 1:9 to 4:1 by weight; a plasticized substance; and a foamed inorganic substance are provided.