10 9. CONCLUSIONS

The present overview aimed to give a brief state-of-the-art report from the wealth of publications that have addressed salts in the deterioration of porous materials. It has clearly shown that the deterioration of porous materials induced by salt crystallization cannot be explained by a single mechanism. It has also made clear that the presence of water and/or moisture in the porous material is as important as the type of salt and the nature, texture, porosity, and interior surface of the material. Moisture transport within a pore system and the changes resulting from variations in environmental conditions—i.e., temperature and RH—are key to understanding the development of the observed deterioration patterns. The synergism that occurs among porous material, salt, and moisture will lead to the “moisture-salt-spiral” (Snethlage et al. 1996, 129) of increasing deterioration rates.