Progress in Organic Coatings 102 (2017) 239–246 Contents lists available at ScienceDirect Progress in Organic Coatings j o ur na l ho me pa ge: www.elsevier.com/locate/porgcoat Coating’s influence on water vapour permeability of porous stones typically used in cultural heritage of Mediterranean area: Experimental tests and model controlling procedure Giorgio Pia a , Carola Esposito Corcione b,∗ , Raffaella Striani b , Ludovica Casnedi a , Ulrico Sanna a a Dipartimento di Ingegneria Meccanica, Chimica e dei Materiali, Università di Cagliari, 09123 Cagliari, Italy b Dipartimento di Ingegneria dell’Innovazione, Università del Salento, 73100 Lecce, Italy a r t i c l e i n f o Article history: Received 5 July 2016 Received in revised form 3 October 2016 Accepted 13 October 2016 Available online 21 November 2016 Keywords: Cultural heritage Photopolymerizable methacrylic protective coating Organic-inorganic hybrids Fractal model porosity Pore size distribution Water vapour permeability a b s t r a c t Water vapour flux into the porous microstructure represents a crucial factor capable of influencing the degradation of porous materials. This fact is of utmost importance especially considering materials installed in cultural heritage. The necessity to preserve stone artworks pushes to perform surface pro- tective coatings that create an intermediate sacrificial layer between stone and the environment. High hydrophobicity and high permeability of water vapour must be one of the most important requirements of a protective film. These features depend upon the nature of coatings as well as the porous microstructures. In order to control coatings’ effects and their influence on final water vapour permeability (ı) properties, a new modelling procedure has been proposed. The study is conducted on a porous limestone, namely Pietra Leccese, which is being largely used for historical constructions in Mediterranean. The average experimental water vapour permeability ı exp is 4.83 × 10 -4 and 3.86 × 10 -4 (g/m d Pa) respectively for untreated and treated PL stone, while the average model prediction ı IFU is 4.87 × 10 -4 and 3.77 × 10 -4 (g/m d Pa) respectively for untreated and treated PL stone. The good agreement between experimen- tal and calculated data shows that the proposed modelling procedure could represent a good tool for designing and controlling protection activity on cultural heritage. © 2016 Elsevier B.V. All rights reserved. 1. Introduction In the past, the stone has always been considered strong and everlasting, capable of lasting for thousands of years. Just two centuries ago, it was realised that the stone is also sensitive to degradation and is required to be properly preserved. Consequen- tially, the necessity of new instructions, institutional regulations and the restoring professional figure was raised up. Convention- ally, degradation processes are divided into three forms; chemical, physical and biological weathering. But in reality, this schematisa- tion is not possible. Several degradation factors act synergistically causing the same effects. Owing to this reason, conservation does not imply a single approach, rather there are several techniques and methods proposed to achieve the aim of preserving cultural heritages. In particular, a widespread way to protect monumen- tal artworks is the use of surface protective coatings that create ∗ Corresponding author. E-mail address: carola.corcione@unisalento.it (C. Esposito Corcione). an intermediate sacrificial layer between stone and the environ- ment. Traditionally, inorganic protective coatings were widely used due to their mineral component, which guarantees the physi- cal and chemical affinity with the stone. The most used stones were calcium or barium hydroxides based, sodium or potassium aluminates based and potassium or fluorine silicates based com- pounds. On the one hand, they are preferred for their compatibility with the substrate and re-treatability thanks to the structural and chemical similarity with stone materials. On the other hand, they possess some drawbacks; an intrinsic fragility and low mechani- cal properties. Organic protective coatings originated in the past, when beeswax, vegetable oils and natural resins were used and the commercialisation of synthetic polymeric products started in the XX century. Organic products characterised by high molecular weight can be applied to solvent solutions, water based emulsions or pure state (monomers or oligomers). In the following years, several acrylic and methacrylic, silane/siloxane, fluorinates’ com- pound coatings were widely employed in the restoration fields [1–5]. High hydrophobicity and high permeability of water vapour are the most important requirements of a protective film. In http://dx.doi.org/10.1016/j.porgcoat.2016.10.021 0300-9440/© 2016 Elsevier B.V. All rights reserved.