PURPOSE:To provide flame-retarded timer having enough flame retardance by a method wherein timbers in araucaria family are impregnated with the predetermined amount of partial reactional product of dicyandiamide, phosphoric acid, boric acid and water. CONSTITUTION:Timbers in araucaria family are impregnated with 100kg or more solid per one cubic meters of the timber of partial reactional product of dicyandiamide, phosphoric acid, boric acid and water. Araucaria is the general name of timbers in araucaria family such as agathis or the like and agathis is preferable for flame-retarded timber. The partial reactional product contains guanylurea phosphate, which is produced by reacting dicyanamide with phosphoric acid, guanylurea phosphate, which is produced by reacting said guanylurea phosphate with boric acid, un-reacted dicyandiamide and the like. Since the partial reactional product can evenly impregnate to the timber, the preferable amount of impregnation is 500kg or more by solution per one cubic meters of the timber. If said amount is below 100kg, enough improvement effect of flame retardance is not obtained.
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