Characterization of TEOS/PDMS/HA nanocomposites for application as consolidant/hydrophobic products on sandstones

Extensive studies have been conducted on the conservation of historical stones. Although many different surface-coating materials have been tested to date, alkoxysilane materials and their composites have shown the most promising results. In this study, composites of nano-hydroxyapatite (n-HA) and tetraethoxysilane (TEOS) were prepared and used for sandstone conservation. The effectiveness of the composites in consolidating and conferring hydrophobic properties to sandstone were evaluated by X-ray diffraction, scanning electron microscopy, static contact angle, mercury intrusion porosimetry, mechanical properties and water capillary absorption. The durability of the materials was examined under different environmental conditions by artificial aging tests. Results showed that the introduction of n-HA and hydroxyl-terminated polydimethylsiloxane into TEOS associated with a neutral catalyst could impart to the stone surface a coarser network for vapor transport and a hydrophobic effect for liquid water at the same time when the TEOS-based nanocomposites were applied as consolidant products on sandstones. Moreover, n-HA played an important role in improving mechanical properties and resistance to artificial aging tests but not in changing the color of sandstone samples.