To provide a waterproof material made of an inorganic, flame- retardant urethane composition having a flame retardance higher than that of a conventional composition, which shows an excellent flame retardance at or after application compared to that of a conventional flame-retardant urethane waterproof material without using any phosphorus nor organic substances, reduces the generation of smoke accompanying harmful gas, shows a good joint-following property against conventional concrete structures, especially against expansion joints, requires fewer persons at work and is easily applied to complex-shaped joints without using any organic solvent conventionally used when mixing a flame-retardant substance with a urethane composition.

In a process for improving the flame retardance and the joint- following property of a waterproof material made of a urethane composition, a waterproof material made of an inorganic, flame-retardant urethane composition is prepared by mixing a hardener and an aqueous film-forming inorganic compound with a urethane tar injection filler wherein a urethane resin having an isocyanate group, tar, polyol or the like are mixed.