Abstract: A process for primer coating a steel substrate with a primer coating comprising a silica binder, wherein the binder comprises an aqueous silica sol having a SiO2/M2O mole ratio, wherein M represents the total of alkali metal and ammonium ions, of at least 6:1, and wherein after the primer coating has dried to the extent that it is touch dry, the coated substrate is immersed in water or alternatively kept in an atmosphere with a relative humidity of at least 50%.

Abstract: The present invention relates to a composition for coating a metal substrate which is intended to be fabricated and overcoated, wherein the binder comprises an acqueous silica sol having a SiO2/M2O mole ratio, with M representing the total of alkali metal and ammonium ions, of at least 6:1, and wherein the ratio of the pigment volume concentration to the critical pigment volume concentration is smaller than 1.