Novel Nano-Filled Coatings for the Protection of Built Heritage Stone Surfaces

Mariateresa Lettieri,Mariaenrica Frigione,Maurizio Masieri

doi:10.3390/nano11020301

Abstract

An experimental nano-filled coating, based on a fluorine resin containing SiO2 nano-particles, was applied on calcareous stones, representative of materials used in buildings and monuments of the Mediterranean basin; for comparison purposes, two commercial products were applied on the same substrates. The efficacy of the protective treatments was assessed by analyzing different characteristics of the three experimental/commercial products, i.e., color changes and permeability to water vapor to evaluate the treatments’ harmlessness; capillary water absorption and water stone contact angle to evaluate the protection against water ingress; oleophobicity of the treated surfaces and the behavior under staining by acrylic blue-colored spray paint and felt-tip marker to verify the anti-graffiti action. Finally, the properties of the treated stone surfaces were analyzed also after the application of pancreatin, used to simulate bird excreta (guano). The protective coatings were found to promote graffiti removal, reducing also the detrimental effects due to simulated guano. The experimental nano-filled product, in addition, was able to provide outstanding performance but using smaller amounts of product in comparison to commercial systems.

Highlights

Received: 4 January 2021The protection of stone materials, belonging to ancient buildings and monuments and exposed to environmental agents and atmospheric pollution, is a permanent concern in the Cultural Heritage field
If regions with different water vapor permeability are present in the stone, water may condensate inside the pores generating detrimental mechanical stress; in particular, this phenomenon may occur at the interface between the untreated and treated parts with possible consequent detachments
The nano-filled experimental product was able to act as an efficient protective surface treatment for compact/porous stone surfaces against water/oil ingress and for graffiti staining

Summary

Introduction

The protection of stone materials, belonging to ancient buildings and monuments and exposed to environmental agents and atmospheric pollution, is a permanent concern in the Cultural Heritage field. The application of nanotechnologies has allowed obtaining products with interesting and enhanced properties. In the last few years, the application of materials providing multipurpose properties (such as hydrophobicity and anti-graffiti protection) has been strongly promoted to provide sustainable treatments, reduce maintenance costs and minimize restoration actions. In addition to widely used hydrophobic coatings [4,5,6,7,8,9,10,11], surface treatments for stone have been tested in relation to their ability to reduce damages arising from several decay factors. Physical, chemical, and biological processes may act, in isolation or in combination, yielding to the loss of surface integrity or even to structural failure

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Conclusion