Rendering mortars in Medina Azahara, Part II: Material characterization and alteration causes

Abstract

In the present work, the depicted coat that covers some of the mortars exposed to weathering in the Medina Azahara archaeological site is .studied. That coat is characterized from the compositional and physical viewpoint and the main causes for its decay are determined. The depicted coat is formed by cal cite and iron oxides. It is quite compact and homogeneous. It is approximately 0.1 to 1 mm thick. The depicted coats supposed by lime mortars have CaCO₃ deposits over polychromy rests. Depicted coats supported by gypsum mortars or mixed lime and gypsum mortars have gypsum deposits over polychromy rests. The processes of rendering mortars dissolution and the later crystallization of salts on their surface, together with biological growth, are the main causes of the decay of the depicted coats.