Conservation strategies against graffiti vandalism on Cultural Heritage stones: Protective coatings and cleaning methods

Graffiti paintings, as an act of vandalism, are one of the most severe threats to stone applied in Cultural Heritage. Their cleaning is expensive and in most of the cases, also induce stone damage, such as chemical contamination, by-products and physical changes. In the recent years, the application of anti-graffiti products has been carried out in order to preserve the valuable substrate. Despite the research lines have been focused on the evaluation of cleaning procedures and anti-graffiti products, it is necessary to lead a critical study of the recently reported results, considering the type of stone and the composition of the other key stakeholders, namely the anti-graffiti protective coatings, the paints and the cleaning agents. A brief description of the composition of the most common spray paints used by graffiti-writers in Cultural Heritage stones is also presented. The protective effectiveness of anti-graffiti coatings and the most remarkable findings on stone graffiti cleaning methods are listed and discussed. Anti-graffiti coatings may facilitate the removal of graffiti compared to untreated surfaces, however this efficacy may be compromised on more porous substrates. Moreover, in almost all of the analysed scientific papers, it was possible to remove graffiti without inducing any damage to the substrate. This review paper will allow to help conservator-restores to achieve the optimization of the graffiti cleaning procedures on stones in Cultural Heritage. Finally, some futures research lines are pointed out.