FIELD: building materials.SUBSTANCE: invention relates to polyurethane binder for a composite material based on natural crushed stone and gravel from dense rocks, which can be used in the construction and repair of slopes of railroads and highways, bank protection structures, cone embankments, approaches to artificial structures, as well as in production of facing building products – tiles, blocks, panels. Polyurethane binder comprising a resin, a hardener, a degassing agent and a filler, as a filler contains a surface-modified montmorillonite-PMM, as a resin – polyol or polyamine, as hardener – isocyanate, as a degassing additive – polymethylalkylsiloxane – PMAS, and obtained by preparation of PMM by grafting didecyldimethylammonium chloride to the surface of sodium montmorillonite in aqueous solution during cation exchange, introducing the resulting PMM separately into the resin and the hardener, followed by its dispersion, mixing and homogenizing the resulting suspensions while stirring with PMAS, at the following ratio of components, by weight %: polyol or polyamine 54, isocyanate 40, PMM 5, PMAS 1. Method for using the above polyurethane binder, comprising introducing said binder into gravel or gravel fractions of from 5 to 20 mm at the rate of 2 kg/mthe surface to be treated is uniformly coated with stirring, followed by molding the composite and curing.EFFECT: technical result is an increase in the strength of the material, an increase in adhesion to the treated layer, increase the wear resistance of the treated surface, stability of strength characteristics with frequent freezing and thawing and the influence of precipitation.2 cl, 1 tbl