Enhanced Historical Limestone Protection by New Organic/Inorganic Additive-Modified Resins

Abstract

The Cultural Heritage deterioration is a spontaneous decay process due to water percolation and air pollutant deposition. In this context, novel acrylic (Twinswet, TW) and siloxane-based (Alpha®SI30) resins were exploited starting from commercial products and then modified by adding either a commercial polysiloxane-based additive (TegoPhobe 1500N) or a precursor of SiO2 nanoparticles (Tetraethyl ortosilicate, TEOS) to improve the Vicenza stone surface hydrophobicity. Properties of the coated materials were studied using different techniques such as water contact angle (WCA), capillary absorption, colorimetric and water vapor permeability measurements. Accelerated UV aging and eight-month outdoor exposure tests (at Milan University campus) were also performed to determine the coatings durability. Notably, the addition of both additives slightly enhanced the surface hydrophobicity resulting in WCAs of about 140°, and decreased the water absorption especially for Alpha-based resins. Conversely, a reduction of water vapor permeability was observed, even if within the threshold value of 50%. Concerning the color variation, Alpha®SI30 preserved the stone external aspect; instead, TW smoothly modified the surface color. All of the studied coatings were stable to both UV aging and outdoor exposure. Hence, the present modified commercial coatings revealed to be very promising for the protection of historical monuments.