To study the surface activities and proton mobilities of CaHPO4.2H(2)O phosphates in powdered states, composites have been fabricated by mixing polycrystalline phosphates with polymer or CaO powders. The electrochemical properties of such composites, compressed into pellets, are studied using complex impedance spectroscopy analyses. We measure the critical volume fraction corresponding to the percolation of ionic currents through the solid composites; The influence of adsorbed water molecules on electric properties is clearly shown. Using home made Volta battery devices, the percolation threshold is accurately determined : a very low value of 12 vol.% for the volume fraction of phosphate or 25 vol.% taking into account the cavities, is observed. This low value is interpreted. A model using the effective medium approximation is used to describe some of the experimental results.