A scanning Kelvin probe technique is used to study the influence of chromate (CrO42-) on the kinetics and mechanism of corrosion-driven dclamination processes affecting polyvinyl butyral (PVB) coatings adherent to the intact zinc surface of hot dip galvanized steel. Placing aqueous sodium chloride electrolyte onto a penetrative coating defect establishes an electrochemical delamination cell in which cathodic O-2 reduction at the delamination front is coupled to anodic zinc dissolution at the coating defect by a thin (2.5-5 mum) layer of electrolyte which ingresses beneath the delaminated PVB film. Soluble chromates in the external electrolyte reduce delamination rates by less than 25% because CrO42- anions are excluded from the underfilm electrolyte laver by the delamination cell electric field. In contrast, dispersions of particulate SrCrO4 in the PVB coatings allow CrO42- diffusion directly into the underfilm electrolyte layer and profoundly inhibit delamination. It is proposed that replacement of underfilm O-2 reduction by a self-limiting CrO42- reduction process is the most significant factor in decreasing delamination rates.