Anti-Graffiti Behavior of Oleo/Hydrophobic Nano-Filled Coatings Applied on Natural Stone Materials

Mariateresa Lettieri,Alessandra Morelli,Mariaenrica Frigione,Maurizio Masieri,Mariachiara Pipoli

doi:10.3390/coatings9110740

Abstract

In recent years, graffiti writings are increasingly regarded as a form of art. However, their presence on historic building remains a vandalism and different strategies have been developed to clean or, preferably, protect the surfaces. In this study, an experimental nano-filled coating, based on fluorine resin containing SiO2 nano-particles, and two commercial products have been applied on compact and porous calcareous stones, representative of building materials used in the Mediterranean basin, and their anti-graffiti ability has been analyzed. All the tested experimental and commercial coatings exhibited high hydrophobicity and oleophobicity, thus meeting one of the basic requirements for anti-graffiti systems. The effects of staining by acrylic blu-colored spray paint and felt-tip marker were, then, assessed; the properties of the treated stone surfaces after cleaning by acetone were also investigated. Visual observations, contact angle measurements and color evaluations were performed to this aim. It was found that the protective coatings facilitated the spray paint removal; however high oleophobicity or paint repellence did not guarantee a complete cleaning. The stain from the felt-tip marker was confirmed to be extremely difficult to remove. The cleaning with a neat unconfined solvent promoted the movement of the applied polymers (and likely of the paint, as well) in the porous structure of the stone substrate.

Highlights

Over the last few years, holistic approaches are trying to tackle the global graffiti phenomenon [1].Any proposed solution is shared with all the involved stakeholders, including those who manage graffiti or utilize street art for city regeneration
The open porosity, measured by MIP, was very low (2%); the pore size was mainly between 0.025 and 0.001 μm (Figure 2b)
The products products used used as as an an anti-graffiti anti-graffiti barrier barrier typically typically have haveaa low low surface surfaceenergy energyat at interface, interface, which which results results in in minimizing minimizing the the contact contact with with the theapplied appliedpaints paintsor orinks inksmainly mainlybecause becausethe theprotected protected surfaces surfacesbecome becomewater waterand andoil oilrepellent

Summary

Introduction

Over the last few years, holistic approaches are trying to tackle the global graffiti phenomenon [1]. Any proposed solution is shared with all the involved stakeholders, including those who manage graffiti or utilize street art for city regeneration. The current studies are addressing to the graffiti removal, and to the knowledge and protection of the street art murals [2,3,4]. Graffiti on building façades, especially those with a cultural and historical value, still remain a vandalism [5]. Several strategies are used to either remove these graffiti or protect the surfaces against their harmful effects [6]. Graffiti removal is expensive and, in some cases, may cause stone damage due to chemical contamination, by-products formation and physical changes

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Results

Conclusion