PURPOSE: To improve the rust-proofing property of a metallic material embedded in concrete, etc., by successively coating and impregnating an aqueous solution of inorganic salts and/or silicate and a treating agent composed mainly of an organic titanate to the surface of the concrete, etc., containing a metallic material.

CONSTITUTION: An aqueous solution of inorganic salts (e.g., aqueous solution of calcium nitrite) and/or an aqueous solution of a silicate (e.g., aqueous solution of Na silicate) are applied to and impregnated in the surface of an inorganic material such as concrete containing a metallic material such as reinforcing steel. Thereafter, a treating agent composed mainly of an organic titanate (e.g., isopropyl triisostearoyl titanate) is applied to and impregnated in the coated inorganic material. The surface of the inorganic material such as con crete can be modified by this treatment to increase the affinity, water-repellency and salt-shielding property and improve the rust-preventive property of the metallic material embedded in the concrete. The rust-preventive effect can be further improved by forming a synthetic resin film on the layer of the treating agent.