Protective properties and durability characteristics of experimental and commercial organic coatings for the preservation of porous stone

The application of hydrophobic polymers to stone materials is an effective way to preserve stone artefacts and protect Cultural Heritage from decay. To improve the characteristics and performance of water-repellent treatments, and to avoid the use of harmful solvents, innovative solutions have been widely explored. As recent examples, organic nano-filled photo-polymerizable systems were proposed as free-solvent efficient protective coatings for porous stones. In this paper, the nano-filled coating, based on a methacrylate mixture matrix optimized in previous studies, was applied on two calcareous stone substrates, typical of Apulia Region (Pietra Leccese, PL, and Pietra Gentile, PG). Its characteristic protective properties (in terms of water-repellency, chromatic modification, capillary water absorption, transmission of vapor water, penetration into the stone) were assessed and compared to the same characteristics displayed by two commercial organic water-borne hydrophobic coatings. Natural exposure and accelerated weathering tests were performed to estimate the long-term behavior of the coatings. The characteristic protective performance displayed by the experimental free-solvent photo-polymerizable coating was found greater than those recorded for the commercial organic products.