The ancient gypsum mortars of the historical façades in the city center of Valencia (Spain)

Abstract

In the historical centre of Valencia (Spain), the brick façades of the residential buildings which were built or modified in the end of the XVIII^th century and the beginning of the XX^th century have been protected and decorated with continuous renderings. According to the constructive tradition, the renderings had to be made with lime mortars, but the recent studies allowed to know their real nature: they are gypsum mortars. The main aim of the study has been to know the nature and the technical aspects of the historical renderings of the façades of the centre of Valencia, in order to discover their secrets from a theoretical and experimental point of view. Therefore, together with the examination of bibliographical sources, several samples of the historical mortars have been collected from renderings. The analytical results confirm that the great majority of samples are composed by gypsum mortars, with different degrees of purity and a variable amount of aggregate and lime. Some samples are mixed mortars (gypsum and lime mortars), but there are also examples of pure lime mortars probably indicating a change in the constructive tradition of the city in a historical moment as testified by the presence of buildings with brick walls bonded with lime mortar and gypsum mortars in the rendering. This fact supposes a conscious application of the gypsum in exteriors and the existence of a specific ancient technique. Moreover the analysis of the surfaces of renderings characterized by a specific finishing and several layers of painting, allows us to confirm that organic substances have been applied in order to protect the gypsum mortars from the inclemency of the weather. Definitively, the characterization of the gypsum mortars that cover the historical façades of the centre of Valencia allowed us to discover a particular and distinguishing aspect of the constructive tradition of the city that must be protected and valued in order to achieve its preservation.