Caratterizzazione microstrutturale e mineralogica di intonaci antichi

The preservation of the exterior finishes of the historic buildings plays an extraordinarily important role in the safeguarding of cultural heritage. In fact, the maintaining of the integrity of the finish preserves the aesthetic value of the building and protects the load-bearing structures from chemical and physical degradation phenomena. The ancient plasters are complex composite materials. They are characterized by a great compositional variability related to both the site and the period of the building construction. In the last decades in the restoration works it has been used materials with chemical and phisical characteristics different from those of the original materials. This practice in many cases has compromised irreversibly the value of the architectural heritage as it has amplified the existing degradation phenomena or, at best, affected the aesthetic value of the finishes. Therefore it is more and more widespread awareness of the necessity of a conservative restoration performed through the utilization of raw materials, production and technologies as much as possible similar to those originally adopted. The design of the restoration interventions requires a preliminary characterization of the ancient plasters through the use of advanced analytical techniques able to detect the characteristics of each component, the kind of binder, the binder/ aggregates ratio. This paper shows the results obtained from the mineralogical and microstructural characterization of plasters samples taken from the San Peter Church of San Pietro dating presumably the early eighteenth century and located in the old town of Forenza in Basilicata (Italy). The listed building presents widespread degradations and detachments of the finishes caused by the complete absence of maintenance over the time. The plaster samples were tested by the X-Ray Diffraction (XRD) analysis and the observation at Scanning Electron Microscope (SEM) coupled with Energy Dispersive X-ray (EDX) spectrometer. The obtained results have allowed us to identify the morphology, the size and type of aggregate, the binder component and the products of decay or deterioration