The stone materials in the historical centre of Sassari: distribution and state of conservation

As many other Italian towns, the historical center of Sassari was built using materials of prevailing local provenance. This is the reason why, following the program research of the Progetto Finalizzato "Beni Culturali", the survey of materials constituting the buildings of the ancient city center of this town and of the decay typologies was carried out. All data were filed in a database and two thematic maps were also produced (materials/lithotypes, and weathering). On this basis and by means of a specific software, quantitative evaluations of lithotypes were obtained. The research evidenced that the use of different natural stones was conditioned by their availability and their different petro-physical features. Pedraforte (carbonatic conglomerate), showing better features but of limited availability, has been used for those portions of the buildings that needed better performances. Marly limestone and calcarenite are the most abundant materials. In particular, marly limestones, occurring in the immediate subsoil of the town, were widely used for plastered walls. Generally, all the surveyed materials display a poor state of conservation, except for those buildings recently restored. Almost all the weathering typologies have been recorded even though some of them are strictly correlated to a specific material. Pedraforte and ignimbrite are affected by alveolization whereas artificial patinae, erosion and granular disintegration have been mainly recorded for marly limestones and calcarenites. Oxalate patinae evidenced on Pedraforte in some buildings are possibly related to the use of organic matter for protective or even decorative purposes. A detailed study of the main facades of some relevant monuments contributed to a further understanding of the behavior of these materials whenever used as building stone and provided a useful tool for a correct restoration and conservation. The study also allowed to identify the exploitation areas of the main building materials used in the historical architecture of Sassari. Some of them are currently obliterated by recent building activity, and only few traces are still visible. This aspect evidences the importance of preserving the quarrying sites for their historical and cultural interest and, above all, for possible provisioning for restorations.