Mass-transfer to a rotating disk electrode has been studied in the case of an interface covered by porous inert layers of thickness delta(f) through which species are transported by molecular diffusion with a diffusivity D-f. In this study, the porous layer consists of a gel deposited on a gold electrode and the species used as tracers are Fe(CN)(6)(3-) and oxygen. The method is based on the analysis of tracer reduction current under total mass transport control (diffusion plateau of the species). The tracer concentration gradient is distributed between the porous layer where mass transport is only determined by molecular diffusion and the electrolyte solution where mass transport is governed by convective diffusion. Two techniques are used here namely electrohydrodynamical impedance (EHD) and a steady flow technique. From the proposed physical model, the diffusion time (delta(f)(2)/D-f) is obtained by regression of the impedance data while the steady state current data yields the diffusion rate (D-f/delta(f)) through the porous layer. By combining the EHD and steady state data, a separate determination of delta(f) and D-f is available and allows the calculation of the porosity of the film. A comparison between the two tracers on the same layer has been made.