Abstract
Alkoxy-based consolidants are widely used for conservation of cultural heritage objects made from sandstones. Even if such consolidants were introduced into practice already in the 19th century, their performance has been enhanced by several modifications to their composition only recently. To obtain a relevant comparison of their application potential, both commercial (Remmers KSE OH and SurfaPore FX SB) and a self-developed particle-modified ethyl silicate consolidant supplemented with two phosphate-based ones, were assessed. Importantly, the potential toxicity of our novel consolidants was considered. Since the stone substrate should mimic the properties of naturally weathered stone, sandstone from the Msene quarry in Central Bohemia, characterized by a high porosity and relatively low mechanical strength, is selected. From practical point of view, the long-term durability of the consolidation effect is crucial compared to the initial level of consolidation. Regarding the determination of durability of the sandstone consolidation according to an American Society for Testing and Materials (ASTM) accelerated weathering test, we performed mechanical tests in micro- (nanoindentation) and macroscale (drilling resistance measurements). The cohesion of the consolidant xerogels in the pores were determined by sorption experiments in gas phase. The durability of our TiO2 and ZnO particle-modified consolidants is superior to that of the commercial products. The aqueous diammonium hydrogen phosphate-based consolidant, which also shows exceptional durability, reveals itself to be a promising product for not only carbonate but also sandstone materials.
Highlights
Alkoxysilanes have been the most widely used stone consolidants since the 19th century [1].Two compounds have been dominant: methytrimethoxysilane (MTMOS) and tetraethoxysilane (TEOS)
A number of products based on TEOS and its oligomers are available on the market
The sandstone used comes from quarries in Msene, central Bohemia (Czech Republic)
Summary
Alkoxysilanes have been the most widely used stone consolidants since the 19th century [1]. Two compounds have been dominant: methytrimethoxysilane (MTMOS) and tetraethoxysilane (TEOS). A number of products based on TEOS and its oligomers are available on the market. Their advantages are well known: their versatility, chemical stability, low viscosity, the ability to form silicon–oxygen–silicon (Si–O–Si) bonds [2], harmlessness of the compounds (e.g., water, ethanol) formed during gelation, avoidance of over-consolidation of the stone surface and, last but not least, cost effectiveness and ease of use. Silicon–oxygen bonds are contained in many minerals, thereby contributing to the compatibility between stone and TEOS-based alkoxysilanes. Owing to the advantages listed above, such consolidants penetrate deeply into the stone’s porous system [3]
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