Investigation into the removal of graffiti on mineral supports: Comparison of nano-second Nd:YAG laser cleaning with traditional mechanical and chemical methods

Abstract

This contribution discusses the analysis of polymeric paint layers and the removal of graffiti from historical buildings and sculptures. The main objective of the research is to compare the effectiveness of nano-second (ns) laser ablation with traditional cleaning procedures for the removal of painted graffiti from the surface of monuments. The vast number of various aerosol paints used for graffiti which contain different binders, solvents, and pigments does not allow the use of a single or universal cleaning method. In this study the efficacy of laser ablation was compared with chemical and mechanical cleaning methods. The laser system used for cleaning was a ns Nd:YAG, irradiating at 1064, 532, and 355 nm. Laser cleaning tests were performed on samples of limestone, sandstone, plaster, and brick covered with black, white, and red graffiti paints based on nitrocellulose, acrylic, and alkyd resins. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) were used to characterize paint binders. The morphology of treated surfaces was examined by optical microscopy and SEM. The results indicated the high efficiency of laser cleaning compared to traditional graffiti removal methods. A strong dependence of the efficacy of laser ablation on the paint composition and the porosity of the substrate was observed.