The ancient gypsum mortars of the historical fa?ades in the city center of Valencia (Spain)

摘要

In the historical center of Valencia (Spain), the brick fa?ades of the civil and residential buildings which were built or modified in the end of the XVIII century and the beginning of the XX 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 this study has been to know the nature and the technical aspects of the historical renderings of the fa?ades of the center 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. Mineralogical and petrographic analyses confirm that the great majority of samples are composed by gypsum mortars, with different degrees of purity and a variable amount of aggregate, but also mixed mortars (gypsum and lime mixed as binder) and, more rarely, pure lime mortars were utilized. This indicates a change in the constructive tradition of the city in a specific historical moment as testified by the presence of buildings with brick walls bound with lime mortar and gypsum mortars in the rendering. This result supposes a conscious application of the gypsum in exteriors and the existence of a specific ancient technique. This particular aspect of the constructive tradition of the city must be protected and valued in order to achieve its preservation.