Characterization of Qarh's Wall Plasters, Al-Ulla, Saudi Arabia. A Case Study

During five years (2008 to 2012) of field work in the restoration and conservation of the Qarh's monuments at Al-Ulla northwest Saudi Arabia, many kinds of wall plasters were studied, investigated and analyzed by the following methods: field observations, (visual examination), Optical Microscope (OM), Polarized Microscope (PM), Scanning Electron Microscope (SEM), equipped with (EDS), and X-Ray Diffraction (XRD).Those methods of investigation and analysis helped us determine the Qarh's wall plasters. Four kinds of plasters were identified; white gypsum plaster, white gypsum and lime plaster, gypsum plaster over an insulating layer and lime plaster over an insulating layer. Their main components are gypsum, lime, sand and an additional material for improving plasters properties. Those results helped us to make a correct diagnosis, which is the first step in any conservation strategy.