Stone materials' decay is and has been the object of several studies. In general it has been related to physico-chemical environmental conditions and to the nature of the materials. The material modifications due to degradation are various and complex and are usually peculiar to each material. Consequently, the study of the material degradation is often complicated because the variety of influences such as microclimate, atmospheric composition, and the composition of the material itself. Nevertheless, before an intervention often only few indications are needed to quantitatively know the amount and the nature of alterations suffered by the stone. Our group, after several laboratory experiences, has been able to verify that knowledge of only two parameters, such as soluble salt content and porosity, are sufficient to define the degradation level. In fact soluble salts are directly related to chemical actions and porosity is related to physical changes in the stone materials. Various samples have been examined after exposition to external conditions and those two parameters have been studied. Similar trends for both parameters have been found.