TEOS-colloidal silica-PDMS-OH hybrid formulation used for stone consolidation

The consolidation ofmaterials concept, which consists of introducing a chemical substance (consolidant) into degraded stone, has been applied to architectural conservation. Silicon compounds such as tetraethoxysilane (TEOS) are frequently used as a base for commercial consolidant formulations due to their ability to form a siloxane polymer such as SiO₂. However, the silica xerogels deposited into the stone show poor performance and the gels obtained are non-porous and tend to crack during the drying stage. In order to avoid the fractures and to improve gel properties, we propose the synthesis of a hybrid consolidant basedonTEOSandfillerssuch as colloidal silica (200 nmin diameter)andhydroxy-terminated polydimethylsiloxane(PDMS-OH). Both additives enhance gel properties such as porosity and elasticity, leading to the formation of non-fractured and permeable gels. Characterization of the hybrid xerogel was carried out by nitrogen adsorption and ²⁹Si MAS-NMR. The properties of the hybrid xerogels were compared with those prepared from a formulation based on TEOS (T-ME) with a composition similar to a commercial product. In order to evaluate the effectiveness of the hybrid consolidant, it was applied to tuff-stone of historical monuments in the city of Guanajuato,Mexico. The tuff-stone was also treated with the formulation T-ME. Both treatmentswere studied by determining the percentage of consolidant deposited, evaluating changes in porosity and hardness of the treated stone. The applicability of the hybrid consolidant for the decayed tuff-stone is under study.