Characterization of Lime Plaster of a Portuguese Medieval Monument in the Indian Ocean Coast

The present study aimed to unravel important features regarding the ancient lime plaster of a Portuguese monument in the Indian Ocean coast for the formulation of compatible repairing materials and to determine its condition to plan conservation works. The study illustrates the hydraulic properties of lime used for the construction, the extent of salt intrusion into the plasters, area of intrusion and its source. Wet chemistry results reveal that the dampness and capillary actions led to salt diffusion into the walls and its percolation to different heights of the monument. Due to the intrusion of water into the matrix of the plaster, its inner core becomes less cohesive, resulting in brittleness of lime combination and peeling-off of the upper fabric. Thermal techniques, X-ray diffraction and X-ray fluorescence results identified the mineralogical composition of the construction materials, viz. lime plaster and mortar. Further, they confirmed the uniqueness of lime combination used to build the monument with lime–silica ratio in the range 1 : 1 to 4 : 1 and its transformations over a period of time in saline atmosphere. This study provides an overview regarding the ancient lime plaster used in the monument and may help to devise new compatible materials for subsequent conservation works.