Abstract: Provided is a method of manufacturing incombustible wood that enables maximization of the amount of an incombustion agent used to be impregnated into wood. Further provided is a method of manufacturing incombustible wood that completely satisfies incombustible-wood conditions required by the Building Standard law and that can be relatively easily manufactured. The method of manufacturing incombustible wood includes performing plural times of individual drying steps for drying wood (for example, board material B), decompression steps for decompressing the wood, decompression impregnation steps for impregnating the wood with an incombustibility treatment agent in a decompressed state, and compression impregnation steps for impregnating the wood with the incombustibility treatment agent in a compressed state, wherein two times of the individual decompression steps, individual decompression impregnation steps, and compression impregnation steps are performed, and three times of the drying steps are performed.

Abstract: A fire-proof treatment solution capable of resolving problems, such as low solubility leading to low concentration and hence low combustion inhibiting effect and water solubility leading to a disadvantage of eluviation, of boron compounds used as a constituent of a flame-retarding treatment solution. In particular, a fire-proof treatment solution produced by adding phosphoric acid and a silane coupling agent to a weak acid or weak alkali aqueous metal salt solution containing a boron compound to thereby obtain a mixed aqueous solution and adding a plant extract composed mainly of a polyphenol compound to the mixed aqueous solution. This fire-proof treatment solution can be widely applied to members composed mainly of cellulose, such as wood, paper and natural fibers. This fire-proof treatment solution can increase the fixation of chemicals to thereby attain a high combustion inhibiting effect and can minimize the occurrence of eluviation.