Compatibility and Efficacy Evaluations of Organic Protective Coatings for Contemporary Muralism

Contemporary muralism is a constantly expanding form of urban art, whose preservation is highly debated and for which no specific preventive conservation measures have been defined. The degradation of painting materials remains a dramatic issue as mural paintings undergo rapid and inevitable chemical–physical reactions, leading to their aesthetic decay and chemical–mechanical disintegration. This work started with interviews with, and questionnaires given to experts in the field from which various needs emerged, including defining a testing protocol for the study of the compatibility and effectiveness of organic coatings to protect street art painted surfaces. Five protective formulations available on the market were selected and applied on mock-ups realized with three different types of paintings (alkyd, acrylic, and styrenic). The efficacy and affinity of the five protective treatments in relation to the different underlying painting layers were investigated. The adopted testing protocol enabled understanding the protection efficacy and compatibility of the different tested formulations in relation to the type of painting and wall preparation. The typology of the underlying paint mainly influences the final aesthetic result, while the application of the primer may play a relevant role in terms of the protection effectiveness, confirming the importance of pre-treating the substrate before painting. The results clearly show that there is still no specific and effective protection system that is appropriate for all commercial paints used by street artists.