Chemical and mineralogical investigations of lime plasters of medieval structures of Hampi, India

A groundbreaking analysis of the medieval lime plasters at Hampi, India, reveals the presence of aragonite and vaterite—polymorphs of calcite—that significantly influence the plaster's crystallization due to self-healing processes driven by wet-dry cycles and magnesium. This discovery sheds light on the durability and degradation mechanisms of these historical materials, with increasing solubility of metastable calcite leading to water dissolution and loss of plaster. The study employed advanced techniques such as X-ray fluorescence (XRF), petrological microscopy, granulometric analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) to characterize the mineralogical, micro-structural, and chemical composition of the plasters. Granulometric analysis indicated the inclusion of granitic aggregate grains, suggesting medium transportation before deposition in a fluvial river basin. Petrological and SEM studies further identified essential minerals like quartz, orthoclase, plagioclase, clay components, chlorite, and cristobalite, with the latter two potentially originating from the river sand of Tungabhadra. These findings provide crucial insights for tailoring compatible lime plaster for future conservation efforts at this UNESCO World Heritage Site.

Singh, M., Kumar, S. V., & Sabale, P. D. (2018). Chemical and mineralogical investigations of lime plasters of medieval structures of Hampi, India. International Journal of Architectural Heritage, 13(5), 725–741. https://doi.org/10.1080/15583058.2018.1469175