Historic incised plasterwork of India – Characteristics and microstructure.

• Characteristics of incised plaster from monuments in Delhi are explored. • Marked differences exist between the incised plaster mortar and typical bedding mortars of the region. • The use of organic fibres and recycled components from an older mortar is seen. This paper reports the characteristics of decorative incised plaster works of New Delhi, from historic monuments belonging to 13th to 16th century C.E. Visual examination of the historic plasterwork depicts that these are made of two layers; a base coat which is coarser in appearance and a finer finishing coat, which is the incised plaster layer. For making the intricate patterns in the incised layer, a thick coat of plaster is applied first and patterns are carved out before the initial set of the mortar, which later hardens to form a very dense microstructure. In order to consolidate and restore the deteriorated portions of the existing plasterwork, the characterisation of the original plasterwork was essential. This was performed by a comprehensive methodology including physico-chemical and microanalytical tests, which revealed information on basic physical properties, mineralogical composition, characteristics of different phases, and porosity and pore size distribution of the mortar. The results indicate that the incised plaster is made of air lime binder and siliceous aggregates. The mortar is characterised by a very narrow range of pore sizes of about 600 nm. The use of organic fibres and inclusions from an older mortar are also evident in the analysis. [ABSTRACT FROM AUTHOR]