A theoretical model for describing the time evolution of concentration profiles in thermal electro-poling experiments is being presented. The model is based on a Monte Carlo formalism. It takes into account the field dependent mobility of cations as well as electrons. Model calculations are presented for a 46S4 bio-glass. Upon application of a DC field Na+ ions start to move toward the cathode giving rise to a depletion zone. The electric field increases in this zone. Once a specific threshold value is reached the electrons become mobile and move toward the anode leaving behind a basically neutral zone. Thus, the full double layer capacity has developed after a few seconds. The concentration depletion profiles continue to develop on a much longer time scale of tens of minutes. In the 46S4 glass Na+ ions as well as Ca++ ions develop a depletion profile. The numerical calculations account for all essential experimental observations available in the literature. The model is also capable of predicting under which conditions two different cations move on the same or on different time scales. (C) 2015 Elsevier B.V. All rights reserved.