Chemical and petrophysical methodological protocol in the consolidation and protection of altered stones in historical monuments

A consolidation or protection is often necessary in the rocks used in Cultural Heritage in order to improve some significant physical properties (decrease of porosity, increase of mechanical-strength), maintaining high vapour-permeability. In this paper a methodological-protocol, developed on the basis of different characteristics of some known Italian lithologies (limestones, marble, pyroclastites), chemical composition of treatments and environmental conditions, is presented. This protocol is now being refined through an experimentation on similar lithologies frequently used in the medieval buildings of Sardinia. The methodology requires a preliminary rock characterization in order to evaluate petrophysical and chemical-mineralogical characteristics and alteration degree, necessary to propose suitable consolidation and protective treatments. Then, the chemical-physical-mechanical characteristics of some products (silicon-based compounds, (metha)acrylic polymers) have been considered. Their strengthening or protective efficacy have been evaluated on the basis of the lithological substrate, its state of conservation and the main environmental conditions which are responsible of its decay.