Abstract: Coating composition suitable for coating a metal, preferably steel, substrate which is intended to be fabricated and overcoated, said composition comprising: i) zinc powder and/or a zinc alloy and ii) a modified silica sol comprising colloidal silica particles modified with 6-40 wt % of one or more silane compounds, based on the combined dry weight of silane compound(s) and colloidal silica particles, and being obtainable by adding said silane compound(s) to a silica sol with a rate of not more than 20 silane molecules per nm2 colloidal silica surface per hour. This coating composition has a relatively long pot life, good white rust resistance, and good film properties.