Graffiti removal from granite cladding by abrasive water-jet

This study focuses on the assessment of a graffiti removal system based on abrasive water-jet technology (AWJ). Spray paints were applied on samples of an important Italian granite commercially-named as “Rosa Limbara”. This granite has been used worldwide as dimension stone for paving and cladding. Two different commercial abrasives have been added in the high-pressure water-jet in order to clean the granite saw-plane surfaces from graffiti. After a check by the naked eye, different criteria have been chosen for assessing the effectiveness of the cleaning process: the similarity in roughness (Ra, Rz, and Rmax) between the original surface and the one resulted after cleaning, the total colour difference (ΔE) and the depth of material removed by the AWJ action. The tests showed that excellent cleaning results can be achieved with both abrasives by correctly combining the operational parameters of the technology (i.e., water pressure, spacing between passes, stand-off distance, travel speed and abrasive flow-rate) without giving any damage to the stone material. The two abrasives showed good results in total colour difference although one of them gave better results in both roughness difference and material removal. Economic considerations on paint removal with AWJ technology are also offered.