Abstract
Reversibility is a mandatory requirement for materials used in heritage conservation, including hydrophobic protectives. Nevertheless, current protectives for stone are not actually reversible as they remain on the surfaces for a long time after their hydrophobicity is lost and can hardly be removed. Ineffective and aged coatings may jeopardise the stone re-treatability and further conservation interventions. This paper aims at investigating the performance of PHAs-based coatings for stone protection, their main potential being the ‘reversibility by biodegradation’ once water repellency ended. The biopolymer coatings were applied to three different kinds of stone, representative of lithotypes used in historic architecture: sandstone, limestone and marble. Spray, poultice and dip-coating were tested as coating techniques. The effectiveness and compatibility of the protectives were evaluated in terms of capillary water absorption, static and dynamic contact angles, water vapour diffusion, colour alteration and surface morphology. The stones’ wettability after application of two commercial protectives was investigated too, for comparison. Finally, samples were subjected to artificial ageing to investigate their solar light stability. Promising results in terms of efficacy and compatibility were obtained, although the PHAs-based formulations developed here still need improvement for increased durability and on-site applicability.
Highlights
The protection of architectural elements against water is one of the main challenges for the conservation of cultural heritage, as water is a major cause of material degradation, which may be physical, mechanical or chemical [1,2,3,4,5,6,7,8]
The performance and compatibility of the protective hydrophobic treatments were investigated in terms of capillary water absorption, static and dynamic contact angles, surface tension, water vapour
Porosity determined untreated andofcoated stones because plays a major role achieved in all the using two commercial water-repellents widely stone conservation, silane and siloxane degradation phenomena that are related to used waterforabsorption and i.e., in athe effectiveness of solution
Summary
The protection of architectural elements against water is one of the main challenges for the conservation of cultural heritage, as water is a major cause of material degradation, which may be physical, mechanical or chemical [1,2,3,4,5,6,7,8]. Protection requires an accurate analysis of the water source and paths and a subsequent design of drain systems to control the water run-off from the top to the bottom of the construction. This is often not possible or not sufficient in heritage buildings, due to several existing restraints. An approach combining chemical and physical protection is often needed to mitigate the problem, and the application of hydrophobic coatings over the exposed surface, preventing water penetration through the material porosity without hindering water vapour transport, has been demonstrated to be an effective solution [4,9,10,11].
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