Evaluation of different gels and poultices to chemically remove graffiti from a Lioz limestone (Lisbon, Portugal)

In recent decades, graffiti paintings have become an artistic manifestation under the label of «Street Art». However, there are still many cases where its application is carried out with vandalic purposes. If we consider historical buildings, they cause an aesthetic alteration and jeopardise the long-term preservation of the stone used. This is why their removal is seen as necessary. In doing so, multiple factors must be considered, such as the stone substrate properties, the composition of the paint, and the cleaning method selected as all of them will determine the effectiveness of the graffiti removal. For this purpose, a study was carried out based on the removal of graffiti paint from a Lioz limestone. This is a stone widely used in the architectural heritage of Lisbon (Portugal). In this article, the effectiveness on the removal of two kinds of spray paints (silver and black), commonly used in this type of vandalism, was evaluated. Different gels and poultices used in heritage conservation were compared as cleaning agents. The aim was to evaluate their effectiveness in terms of graffiti removal, leaving the minimum amount of residues on the surface of the stone. Regardless of the paint, the greatest cleaning level was achieved with gels, mainly with Nevek®. However, further research must be conducted to avoid remains of the cleaning vehicles and chemical contamination.