We present the final results of an extensive aging test, performed at the CERN Gamma Irradiation Facility on two bakelite Resistive Plate Chambers (RPC) detectors. With a method based on a model describing the behaviour of an RPC under high particle flux conditions, we have periodically measured the electrode resistivity ρ of the two RPC prototypes over 3 years. We observed a large spontaneous increase of ρ with time, from the initial value of about 1010Ωcm to more than 200×1010Ωcm. A corresponding degradation of the RPC rate capabilities, from more than 3kHz/cm2 to less than 200Hz/cm2, was observed; the reversibility of the process, using a humid gas mixture, has also been studied. We also present a study of the effects of humidity on the bakelite resistivity using two 10×10cm2 bakelite samples.