Possibilities of monitoring the polymerization process of silicon-based water repellents and consolidants in stones through infrared and Raman spectroscopy

The increasing use of Raman and infrared (IR) portable instruments for in situ diagnosis and characterization of materials and their conservation state in artworks, has led us to investigate in the laboratory the real possibilities that both vibrational spectroscopies could have for monitoring in situ and in real time the polymerization process of silicon-based water repellents and consolidants in stones, after application of the corresponding treatments. Initially, we took IR and Raman spectra of the selected conservation products deposited on inert surfaces along several weeks, in order to determine the spectral regions more sensitive to changes as polymerization proceeded. Afterwards, we tried to apply the same protocol to model stone specimens (Bateig stone widely used in the Spanish Architectural Heritage) impregnated with the conservation products. The stone was characterized, and weight recording, colour variation and SEM observations were carried out once a week during 6 weeks in order to complement the protocol. As far as silicon-based conservation treatments applied to calcite containing stones refer (as the Bateig one here employed), we do not foresee possibilities for in situ infrared reflectance spectroscopic monitoring of the corresponding polymerization processes. In the case of the Raman technique, stone fluorescence represented an additional problem. If it can be overcome, Raman data could provide some clues for assessing the polymerization state, especially for the consolidant case.