This work investigates the hidden interface between a conversion-coated zinc surface and a polymer coating upon exposure to an electrolyte by simultaneous in situ ATR-FTIR and EIS. Various system properties were distinguished, such as the ingress of electrolyte constituents, and an active process of water-induced alterations of the conversion layer. The interface between a polymer film and a surface treated metal surface is of considerable fundamental and technical interest in many areas of application, and the results obtained open up the use of this method for a wide range of important applications. © 2010 Elsevier B.V. All rights reserved.