Salt deterioration of porous materials subject to repeated cycles of wetting and drying

We have investigated the damaging of sandstones in the presence of sodium sulfate during wetting and drying cycles. We have shown that the interfacial properties of the salts play a major role in the process and have elucidated which crystalline phase is responsible for the mechanical damage. We find that damage is due to the transformation of thenardite (anhydrous) to mirabilite (hydrated crystals) during wetting and drying without the complete dissolution of the anhydrous crystals. As the volume change is large, this is likely to be the major cause of the mechanical damage observed in the sandstone. Second, we find that the interfacial properties of the different crystalline phases play a major role on whether the salt solution will effloresce (crystallize on the outer surface of the stone) or subfloresce (crystallize within the stone).