The model stresses the role played by the distribution of the current lines around the blockers and by the dielectric properties of these blockers. When the matrix conductivity is low enough, isolated spaces appear on both sides of the blockers. This model is consistent with most of the experimental features of ion-blocking in conducting ceramics, including the decrease of the blocking factor with temperature and the similarity between the bulk and blocked conductance activation energies. The admittance diagram parameters can be correlated to the geometrical parameters of the blockers. Additional relevant results obtained with alumina-zirconia composites reveal the limits of the model.