Abstract
Mechanical methods to extract undesired graffiti paints on ornamental stones are efficient cleaning methods from an economical point of view. However, effort on the optimization of mechanical cleaning procedures to avoid any damage to the substrate is required for large areas. In this study, two ornamental stones with different composition and texture, and which are commonly used in Spain and Portugal were selected: Granite Vilachán and Limestone Lioz. Moreover, the most common surface finishes were selected-disc-cutting and bush-hammering to simulate the stones found in buildings. Two graffiti spray paints were selected: Blue Ultramarine and Silver Chrome. As cleaning methods, three soft-abrasive blasting procedures: Hydrogommage (mixture of air–water–micro grained silicon abrasive), IBIX (mixture of air–micro grained silicon abrasive), and dry-ice procedure (carbon dioxide ice pellets), were tested at pressure below 0.4 MPa. The methodology for evaluating the effectiveness and harmfulness of each cleaning method was based on stereomicroscopy, scanning electron microscopy, color spectrophotometry, and confocal microscopy. As result, IBIX achieved the highest level of graffiti paint extraction although this method increased the surface roughness. Conversely, cleaning based on dry-ice projection did not achieve a satisfactory extraction of the graffiti, mainly of the blue paint. Dry-ice blasting can induce acid environments and IBIX causes dust emission during the projection. Hydrogommage was the most efficient cleaning method amongst the tested procedures, because it induced the lowest roughness change and although the graffiti extraction was not complete, it achieved the highest removal level. Therefore, the most satisfactory cleaning method was that achieving a satisfactory extraction level, minimal modifications of the surface roughness, an economic suitability, an environmental integration, and lower human health risks.
Highlights
Stone materials from buildings and monuments are commonly vandalized by uncontrolled graffiti application, leading to serious threats to the aesthetic of the building and to the conservation of historic and artistic pieces [1,2,3]
The aim of this paper is to evaluate the cleaning effectiveness and harmfulness of three soft-blasting methods to remove two spray graffiti paints commonly used in vandalism, i.e., blue and silver paints
A qualitative evaluation of the cleaning effectiveness of each cleaning procedure was performed according to the classification numbers (CN) [24]
Summary
Stone materials from buildings and monuments are commonly vandalized by uncontrolled graffiti application, leading to serious threats to the aesthetic of the building and to the conservation of historic and artistic pieces [1,2,3]. Graffiti cleaning is an important issue that requires funding by governments and municipalities. An increase of knowledge about graffiti extraction and damages induced on the substrates is required. In most of the cases, graffiti are not shortly removed after their execution due to insufficient human and financial resources. Graffiti paints are usually cleaned after a long exposure allowing graffiti interaction with the environment and the stone. Gomes et al [4] analyzed the influence of SO2 exposure of alkyd and polyethylene graffiti paints and verified the occurrence of physical and chemical alterations on the graffiti paints and the stone–paint coating interactions. It is advisable to carry out conscientious cleaning operations soon after their execution, which is an economical way
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