Ancient gypsum mortars from St. Engracia (Zaragoza, Spain): Characterization. Identification of additives and treatments

Abstract The ancient mortars coming from the alabaster main facade of the St. Engracia Basilica (XVI century). The research has been carried out about the original joint mortars and the repairing mortars of several restorations. The characterization of different types of mortars was made by the application of optical microscopy, scanning electronic microscopy with EDX, X-ray diffraction, infrared spectroscopy and laser granulometry. Gypsum is the main component. There has been studied on the mortars: the composition, the binder/aggregate ratio, the granulometry of the binders and the aggregates, and the identification of the additives (organic compounds.,) used in the mortars. The design of the restoration mortars has been achieved by the knowledge of the studied mortars.