Admixture for concrete and mortar used for preventing capillary absorption and forming waterproof surfaces.In precast concrete elements with painted surfaces, apart from providing water-tightness, HIDROFOB-21 prevents the formation of salt deposits on the surface of concrete. HIDROFOB-21 is also a universal agent for formation of transparent water-repellent impregnation of porous surfaces made of concrete, bricks, natural stone, etc.