Chemical Composition of Hydrophobic Coating Solutions and Its Impact on Carbonate Stones Protection and Preservation

Abstract

The decay diagnosis and conservation of stone-built heritage is becoming a worldwide concern, especially when stone decay causes chromatic changes in the original stone aesthetics, which directly impacts its sociocultural value. Among all the causes of stone decay, water action is identified as the major cause of stone decay and chromatic changes in stone building materials; hence, protective eco-friendly hydrophobic coatings are the efficient and fundamental options to prevent penetrating water into the stone. This paper aims to contribute to tackling water action on natural building stones by studying three different commercial hydrophobic coatings and finding out the correlation between the effectivity, compatibility, and durability of these coatings and the physical, chemical, and mineralogical features of four distinct types of limestone, one calcitic dolomite, four kinds of marble, and one granitoid. Nine different natural stones have been chosen due to their variations in physical, chemical, and mineralogical natures. A multi-analytical approach was adopted through digital microscopy and colourimetry assays to assess the compatibility of the hydrophobic coatings, accelerating ageing in climatic chambers to assess their durability, optical tensiometer analyses to evaluate the hydrophobic effectiveness, and h-XRF and XRPD for determining the chemical and mineralogical composition of stone samples. The results obtained demonstrate that the coating composed of silane/siloxane with modified fluorinated additives (FAKOLITH FK-3 Plus Nano) is the most effective, compatible, and durable coating among the selected hydrophobic coatings. These results can be considered the pioneering steps for developing eco-friendly and cost-effective coatings.

Overview of the challenges and current solutions in organic and hybrid coatings for historical monuments and architecture

“…Coatings which are not breathable or permeable can create a moisture barrier or entrap salt crystals, causing failure of not only the coating, but also the surface by enabling cryptoflorescence. [29][30][31] Commonly, hydrophobicity is used as an initial evaluating measure as it demonstrates the ability to reduce the effects of acid rain and suggests potential for the other resistances and antifouling traits. Fluoropolymers are often used in conjunction with other polymer types to realize these properties; however, with the USA and EU proposing further restricting fluorocarbon-containing substances, their widespread use in coatings will need to be replaced.…”

Evaluation of Fatty Acid Methyl Esters (FAME) as a Green Alternative to Common Solvents in Conservation Treatments

“…An unresolved challenge in this domain pertains to the removal of substances exhibiting low polarity or non-polar characteristics [8,9]. Solvents commonly used for their removal [10,11] pose considerable environmental and health risks, particularly in the case of material such as microcrystalline waxes, which are widely employed as protective coatings for the substrate of diverse artworks [12][13][14][15][16][17].…”