Electrochemical impedance spectroscopy (EIS) measurements were used to investigate the influence of quartz filler concentrations on epoxy coatings structure. The conductivity of isolate coating was explained via two types of percolation structures: one of them was formed by polymeric binder imperfections and the other was referring to defects on the boundary between quartz’ particles and epoxy binder. So the EIS spectra were fit to the equivalent circuit consisting of two parts which included elements relating to fractal dimensions of percolation clusters mentioned above. Studying concentration dependences of equivalent circuits’ elements three critical concentrations of pigment corresponding to different conductive structures in coatings bulk were found. The value of the last coincided with critical volume concentration of pigment estimated by independent method.