Inputs to produce lime mortar for conservation and restoration of Thanjavur Palace, India: characterization study

The present study characterizes mortars from Thanjavur Palace (Thanjavur, India) to illustrate ancient production methods and the raw materials used. The mineralogical-petrographic composition of mortars was determined using optical microscopy, supported by scanning electron microscopy with energy-dispersive spectroscopy and X-ray powder diffraction. The chemical composition and organic content of the binder were also determined. The aggregate-binder ratio and particle size distribution of the mortars were investigated. Results showed that the composition of both the aggregate and binder varied between mortars. The aggregate consisted mainly of quartz, with small quantities of feldspar and individual grains of limestone and other lithic grains present. The majority of the mortars contained a lime binder, but kaolinite was also identified, indicating a clay binder. Kaolinite primarily occurred in bedding mortars rather than plaster mortars. All samples were in a deteriorated state due to the presence of gypsum and halite. Analysis of particle size distribution confirmed the size of the aggregates to range between 1.18 and 0.3 mm, showing that the aggregates must have been ground in order to allow for the dispersion of binders. Furthermore, biomolecules in the form of carbohydrates, proteins and fats, which could serve as natural admixtures to improve properties in both the fresh and hardened state, were identified in all mortar samples.

Automated summary

This study characterized mortars from Thanjavur Palace in India, revealing variations in the composition of aggregates and binders among different mortars. While most mortars contained a lime binder, some also had kaolinite particles. The deteriorated state of all samples was attributed to the presence of gypsum and halite. Analysis of particle size distribution showed that aggregates needed to be ground for binder dispersion, and natural biomolecules like carbohydrates and proteins were identified in all samples as potential admixtures.