Non-destructive analytical techniques for the evaluation of cleaning and protection processes on white marble surfaces

Stone conservation and protection is the focus of several researches, especially for historical buildings, monuments and artworks. The objective of this study is to verify the impact of a helical vortex cleaning process in the surface of white marble samples. Powder abrasive material was used in the cleaning process with posterior application of different nano-compound products like water-repellent, anti-graffiti coating and consolidant. The thickness of the damage layer, the porous size distribution and the surface composition were evaluated with non-destructive techniques: X-ray micro-tomography and X-ray Fluorescence. The results indicated that the marble damage layer ranged from 80 to 180 mu m due to the cleaning process with garnet as abrasive material. The estimation of the average thickness of the dirt layer by X-ray attenuation was 16 mu m. Marble surface porous size distribution indicates that porous links were still present in the surface after the treatment with each one of the nano-compund products and have kept it permeable to air. Silicon, S, K, Ca, Ti, Mn, Fe, Cu, Zn and Sr were identified in the marble surface. Calcium and Sr are from the marble composition, Si from protective solutions applied and the other elements from the dirt layer. (c) 2018 Elsevier Masson SAS. All rights reserved.