Plaster and stone surface restoration of ancient Convicino (Sasso Caveoso in Matera - Italy)

The oldest part of the city of Matera, known as Sassi, is an architectural and urban complex consisting of built and carved out structures that stretches over a karst plateau, of which it seems to be a natural extension. The upper layer of the plateau is formed by calcarenite, a calcareous sedimentary rock of biochemical origin, improperly called tuff, characterized by the ease of extraction and processing which has determined its use as typical construction materials. The Sassi neighbourhood are UNESCO World Heritage since 1993. Moreover, the city of Matera has been chosen as European Capital of Culture for the year 2019 because of its unique architectural heritage that testifies the ability of humankind to dig shelters in the rock since prehistoric times. This paper illustrates a conservative restoration of a whole neighbourhood, currently abandoned and degraded, located in the Sasso Caveoso aimed at its rehabilitation as a tourist building. This neighbourhood develops along two different rocky planes with constructions facing to one side on a driveway and to other one on a series of small squares with walking surfaces following the trend of the underlying rupestrian houses roofing. Both carved out and built structures have affected by different forms of physical and chemical degradation phenomena, mainly due to capillary rise of water. Moreover, internal plasters performed in previous maintenance interventions with mortars based on cement are damaged by detachments caused by different thermal expansions between the masonry and the plaster and the presence of sulphate salts soluble as well. In this conservative restoration, binders based on natural lime were employed to obtain mortars or plaster compatible with the original materials and silicone acrylic resins were used as waterproofing. The severely affected ashlars were replaced by the rip-and-sew technique with calcarenitic blocks taken from a quarry located in close proximity to the City of Matera