Changes in the moisture content and the resulting recrystallisation of the entrained salts is one of the major damage causes in historic materials like natural stones, tiles, plasters and mortars. This paper presents a new development in wireless monitoring of the moisture content in historic mineral materials. In this ongoing research, electrical impedance measurements are carried out to monitor the changes in the measured electrical conductivity of materials, as affected by both the total moisture content and the salt concentration. A measurement system consisting of a pair of electrodes, a sensor board and a low power data acquisition hardware was developed which was optimised for use in wireless sensor networks. Initial results of the laboratory validation tests are presented in the paper.