Technological transfers in the Mediterranean on the verge of Romanization: Insights from the waterproofing renders of Nora (Sardinia, Italy)

The paper reports the results of a multi-analytical characterization study on the renders constituting thewaterproofing coatings of 11 cisterns located in the Punic-Roman archaeological site of Nora (SouthernSardinia, Italy). The multi-layer layout of the coatings is related both to the practice of putting sev-eral strata of render in a synchronic plastering phase, and to frequent restoration activities related tothe prolonged use of the cisterns. The aims of this study are (a) to determine the compositional andtextural properties of the binding materials, (b) to define the coating systems employed in diachronicplastering phases, and (c) to identify the role of diverse cultural influences in the modification of therender recipes along time. The combined interpretation of the results obtained through petrographic,mineralogical, microstructural and microchemical analyses allowed discriminating different render typesemploying various pozzolanic additives, whose utilization is related both to Punic and Roman technolog-ical practices. Furthermore, the cementation processes of the renders were studied through an in-detailmineralogical and spectroscopic characterization of their binder fractions. The results demonstrated thathydraulic reactions were often enhanced through specific treatments of the binding mixtures, such asthe combined use of different pozzolanic additives, the adoption of comminution processes to increasetheir reactive specific surface and the use of saltwater to enhance silica and alumina activity in solutionthrough pH increase. Such technological practices promoted in some cases not only the precipitation ofCa-based pozzolanic reaction products (C-S-H and AFm phases), but also the formation of nanostructuredanthropogenic magnesium-silicate-hydrate (M-S-H) phyllosilicate gels, leading to a further increase ofthe cohesive properties of the binding mixtures. A combined interpretation of the results with the cisternconstruction chronologies confirmed that cistern coating techniques in Nora were still largely influencedby Punic traditions even two centuries after the Roman conquest of Sardinia.