Historical structure rehabilitation, including repair and maintenance, is an increasing trend. Replacing the damaged material with a modified material that has suitable properties is a particular technique. The adoption of an affordable, environmentally beneficial, and sustainable natural polymer admixture is suggested in this study. Terminalia chebula is the polymer extract that is added to the lime mortar. The main objective of this research is to examine how the mechanical and fresh state characteristics of lime mortar alter when a natural admixture is added. Modified lime was used in the study to investigate fresh state properties such as consistency, workability, and setting time. After 28 days, tests of the mechanical characteristics, including compressive and flexural strength, were conducted. The characteristics of lime mortar were found to be more significantly influenced by the admixture. When compared to traditional mortar, the inclusion of natural admixture had favourable results in terms of mechanical qualities and fresh state.