APPLICATION OF DIFFERENT METHODS OF SURFACE ANALYSIS FOR THE EARLY DIAGNOSIS OF ART STONE (CALCATRENITE)DETERIORATION

The deterioration process of historical building is progressive and irreversible, and the timing and mode of impact are different depending on the characteristics of building materials used, local microclimate, air pollution, presence of specific flora and fauna. The surface structural characterisation of building materials is mandatory in preventing and eventually recovering degradation effects. Ideally, the analysis of structural stones should be complete, efficient, rapid, and non destructive when dealing with a precious or unique construction. For this purpose a building sample (ca. 1m3) was constructed by using calcarenite stones (33x15cm), collected from a local quarry, and placed between the archaeological site of Lavello, a little town located in the Basilicata Region (Italy), and the industrial area surrounding this town. In this case study in progress on the degradation of stone materials, we set as an objective the characterization of the state of conservation of stone surfaces. The intact calcarenite stone was characterised by using different methods of surface analysis (XRD, XPS, SEM), and exposed to outdoor conditions. The analyses of the stone material were repeated after three and six months to early evaluate the progression of alterations and the forward modifications of calcarenite structure. Results obtained by using all the applied surface analysis methods were compared. Climatic parameters (temperature, light irradiation, wind intensity, humidity), and air pollutants (SO2, CO, NOx, O3, and heavy metals) were determined. Biological attacks on the surface of calcarenite stones were also investigated. After only three months of the stone sample exposures, the adopted analytical methods were able to provide a series of data, which as in the arrangement of a simple jigsaw puzzle, allowed the assessment of the incipient modification of the stone surfaces confirmed by observations performed on six months replicates, given that climatic conditions and air pollution undermined the structure and the compactness of stones favouring the biological colonization especially in the South–East direction of prevailing winds.