PSI - Issue 55

Jéssica D. Bersch et al. / Procedia Structural Integrity 55 (2024) 57–63 Bersch et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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1. Introduction Graffiti is a commonly seen source of damage (Rossi et al., 2016), especially in urban areas (Moura et al., 2016), which affects not only recent buildings with low significance but also façades with historical and artistic value (Pozo Antonio et al., 2016). In fact, as reported by Lettieri et al. (2019), although graffiti writings might be observed more frequently as an art expression, mainly their presence in historical buildings is still understood as vandalism. Typically, spray paints are used for graffiti applications; the spray paints are composed of a pigment, a binding medium, and a solvent (Sanmartín et al., 2014). Regarding the removal of graffiti applications, it seeks to recover the former esthetical properties of the affected surfaces and reduce physical-chemical consequences on the substrate arising from the graffiti paint (Feltes et al., 2023). However, graffiti removal may be challenging concerning the high costs involved (Pozo-Antonio et al., 2016) and the adherence of the paint to the surface (Feltes et al., 2023), which can even prevent its total extraction, further than altering the surface characteristics (Pozo-Antonio et al., 2016). Although unauthorized graffiti, as an anthropic hazard, can be painted over, this may not be the best approach (Sanmartín et al., 2014) aiming to solve the problem durably, especially in case of historic buildings. Therefore, prevention is regarded as a promising approach (Carmona-Quiroga et al., 2010a). Thus, to protect the building surfaces against unwanted vandalism, anti-graffiti products can be applied; the protective products are available as sacrificial, semi-permanent or permanent coatings, which, respectively, are eliminated during graffiti cleaning, can withstand two or three cleaning cycles, or, finally, may resist to more than ten cleaning cycles (García and Malaga, 2012). Generally, anti-graffiti coatings act as protective barriers, which prevent the penetration of the paint within the substrate (Moura et al., 2014) and facilitate its cleaning due to the resulting energy of the surface (Lettieri and Masieri, 2014; Rabea et al., 2012). Moura et al. (2017) investigated sacrificial anti-graffiti products composed of SiO 2 nanoparticles or water-based organoxiloxane emulsions with special additives; the studied permanent products were water-based fluoroalkylsiloxane and an aqueous nanostructured emulsion of silicon-based molecules. In fact, the majority of commercial anti-graffiti products are siloxane/silicone-based, as they can repel most water-based paints and markers; however, they may not be able to protect the surfaces against oil-based paints, which require the protective solutions to be oleophobic or superomniphobic (Bayer, 2017). Hence, to avoid paint penetration, the anti-graffiti products should ideally be hydrophobic and oleophobic, with low surface energy (García and Malaga, 2012). In addition, anti-graffiti coatings should be transparent (Rossi et al., 2019). Moreover, the efficiency of the anti-graffiti actions depends on the staining agent, the cleaning procedure, and the affected substrate (Lettieri et al., 2019). Regarding metallic substrates, for instance, smooth surfaces are more favorable for graffiti removal (Rossi et al., 2016). There may be a compromise between the protection provided by the anti-graffiti solutions to the underneath surface, favoring the prolonged service life of paintings and façades, and their effects on the substrate properties. Gil et al. (2023) reported impacts on the surface gloss, hydrophobicity, drying capacity, and water absorption by capillarity of External Thermal Insulation Composite Systems (ETICS) when applied with anti-graffiti products. Moura et al. (2016) verified physical alterations on Portuguese limestone and painted and unpainted lime-based mortars, including water absorption, drying behavior, and water vapor permeability; the porous and capillary structure of the substrates may affect the impregnation of the anti-graffiti products, and, therefore, the capillary water absorption (Moura et al., 2016). Currently, the long-term performance of building materials is emphasized within the sustainability context: durability and resilience of the materials can be affected by the existing scenario of a changing climate (Lacasse et al., 2020), whose impacts are surrounded by significant uncertainty (Wallace et al., 2021). García and Malaga (2012) have already referred to the need for anti-graffiti products to be friendly considering building users and the environment. The importance of the topic actually relies on global warming as one of the major current challenges (Yassaghi et al., 2019) and the need to investigate preservation strategies under climate change (Blavier et al., 2023; Xiao et al., 2021). The application of anti-graffiti products may impact the maintenance economy (Carmona-Quiroga et al., 2010b); successful building maintenance cost estimation plays a role in the circular economy, so as strategies to deal with construction waste (Mahpour, 2023). Furthermore, preserving the existing buildings, seeking sustainability, and reducing maintenance energy and efforts is essential. In this context, the present study aims to discuss, based on the available literature, how anti-graffiti products and their efficiency may be affected by the changing climate and, on the other hand, how their performance and durability can represent different scenarios.