Abstract
The application of hydrophobic treatments to stone surfaces is the most common proven method to prevent, or at least limit, the degradation of stone-made constructions and artworks brought about by the ingress and action of water, in particular in the case of very porous stone materials. To avoid the use of protective products containing harmful solvents, new green products have been proposed. In this paper, an eco-friendly hydrophobic coating, based on a fluorine polymer dispersed in water, was deeply analyzed to evaluate its protective properties, especially for very porous stone substrates. To this aim, a wide characterization of treated and untreated Lecce stone elements, i.e., a stone typical of the Apulia region, was carried out to assess the optimum required amount, the effectiveness and the protective capability, even against graffiti staining, of the green hydrophobic treatment, still allowing the stone to retain adequate vapor permeability. The efficacy of the eco-friendly product was analyzed also after a short time (four weeks) of outdoor exposure. Suitable performance and short-term durability of the green hydrophobic coating were found, comparable or even greater than those reported in the current literature for other widespread commercial products, confirming the capability of the product to preserve porous stone surfaces even in absence of solvents in its formulation. The study also allowed to experiment with the “contact sponge” test as an appropriate method for evaluating the water absorption properties of the stone.
Highlights
Porous stone materials, such as Lecce stone, Noto stone, Globigerina stone, Ançã stone, Tuffeau limestone, Maastricht limestone, have been widely employed since ancient times to realize buildings, monuments, ornaments and other works of art, in UNESCO WorldHeritage sites [1], in many European countries [2] and in the Mediterranean regions
The observed colored variations are lower than those obtained after the application of other commercial protective products on Lecce stone. ∆E*ab around
An eco-friendly hydrophobic coating, based on a fluorine-based polymer dispersed in water, was analyzed as surface treatment able to protect a very porous stone, i.e., Lecce stone
Summary
Heritage sites [1], in many European countries [2] and in the Mediterranean regions (such as the southern Apulia [3], Sicily [4], and Malta [5]) Their characteristic high porosity makes them suitable for being worked and modeled to create true masterpieces; this feature is, at the same time, responsible for their high vulnerability towards environmental agents, foremost water; they can undergo degradation which compromises their mechanical characteristics, functionality and external appearance. Preservation and conservation procedures must be, carried out employing appropriate materials and technologies that take into account the level of conservation/degradation of the stone, the conditions of exposure, the function of the stone element The use of such protective materials allows limiting restoration/maintenance interventions, or even the demolition of a building, with the necessity to rebuild it, with obvious savings in terms of time, costs and material resources. The use of protective/conservative treatments, represents an advantage from a sustainability point of view
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