Stucco (specifically lime-based mortar and plaster) was known and used by the people of the Harappan civilization, including at sites like Mohenjo-daro and Kalibangan. 

Composition: The ancient material, sometimes referred to as sudha in later Sanskrit texts, was typically a compound of quick-lime and sand, occasionally mixed with gypsum.

Function over Form: During this early period (third millennium BCE), the use of stucco was primarily functional rather than decorative.

It served as a durable and water-resistant mortar for cementing brick structures and was especially important for plastering areas prone to seepage, such as drains and the floors of baths (e.g., the Great Bath at Mohenjo-daro, which used gypsum plaster and bitumen for waterproofing). The Harappan people possessed the technical knowledge for burning lime to prepare this mortar.