Solvent effect on TEOS film formation in the sandstone consolidation process

Abstract

Alkoxysilanes, low-viscosity monomers capable of polymerizing into the porous network of stone by a sol-gel process, are widely used as consolidants in the restoration of stone monuments. However, since consolidation is a non-reversible application capable of causing serious harmful side effects to the original material, stone consolidation is almost always considered a very risky intervention. Alkoxysilanes are insoluble in water, so co-solvented systems are very often used, but even knowing that the solvent is a determinant parameter for sol-gel reactions, there is still a lack of information regarding how it can influence the stone-alkoxysilane affinity. For two different tetraethoxysilane-acidic co-solvented systems we are reporting both the morphological characteristics showed by gels formedin situ and the affinity reached with the stone in the sandstone consolidation process. Aqueous solutions of ethanol and methyl-ethyl-ketone (MEK) were the solvents compared. SEM and ²⁹Si Solid State NMR were used todetermine the alkoxysilane performance on these silicic-based materials. It was found that using MEK solutions resulted in appreciable sandstone-alkoxysilane interaction, forming a more homogeneous film. On the other hand, ethanol does not promote alkoxysilane-sandstone compatibility. A brittle film is obtained when ethanol is used.