Characterization of 12th-century brick-lime stepwell plasters from New Delhi, India

•The plaster composition, microstructure, mineralogical and hydraulic properties of brick–lime junction were studied using analytical instrumentation techniques.•SEM indicated the formation of calcium silicate hydrate and calcium aluminate hydrate at brick-lime junction making the plaster feebly hydraulic.•Variations in elemental compositions (important major/minor components) of brick, brick-lime junction, and calcite matrix were examined under EDX.•XRD showed the main crystalline phase of brick as quartz, feldspar, cristobalite, biotite, muscovite and mullite.•Organic additives analysis by SEM showed the inclusion of Jute fibre.