An ORP-EIS approach to distinguish the contribution of the buried interface to the electrochemical behaviour of coated aluminium

•An integrated ORP-EIS approach is used to study the bare and coated substrates.•A two-layer EEC is employed to follow the individual ion diffusion separate from water uptake across the coating.•Prior to the arrival of the ions at the buried interface, the barrier properties of the coatings are independent of the surface pre-treatments.•The correlation between the diffusion of ions and interfacial influences is unravelled.•The electrochemical contribution of the buried interface is characterized showing the influence of the different surface pre-treatments.