A solvent-free undercoat composition for corrosion control at welds and other repair sites on plastic-sheathed steel pipes with and without cathodic protection, including a component K1: a water-based rubber dispersion for formation of a barrier layer for isolating the metallic repair site from oxygen, water vapor and water penetrating from externally; a component K2: a water-based resin dispersion for adhesion on the metallic surface of the repair site and on the nonpolar surfaces of the plastic sheathing; a component K3: an aqueous emulsion of prehydrolyzed organofunctional silanes for accelerating the drying, for improving the adhesion to the metallic surface, particularly at elevated temperatures, and for increasing the resistance to cathodic disbondment.