Multi-analytical Studies of Archaeological Chinese Earthen Plasters: The Inner Wall of the Longhu Hall (Yuzhen Palace, Ancient Building Complex, Wudang Mountains, China)

The Yuzhen Palace is one of the nine palaces in the Ancient Building Complex built by order of the Yongle Emperor during the Ming dynasty. The buildings were built with dressed black bricks. As a result of the planned national South-North Water Diversion project, the water level in the Danjiangkou Reservoir that surrounds the Yuzhen Palace was expected to rise by approximately 15m. To avoid submersion of the site, three gates were elevated by 15m in 2013 and other buildings dismantled, for later reconstruction. The characterization of the construction materials has therefore become of primary importance. Here, we present results on the plasters of the Longhu Hall. The analysis of materials involved a multi-analytical approach combining optical and electron microscopy with X-ray and vibrational spectromicroscopies and thermogravimetry. The results indicated the use of two earthen plaster layers and a whitewash finish coating applied over a thin preparatory intermediate layer to improve the adherence of the finish coating to the earthen plaster. Ramie and straw fibres identified in the earthen plasters were added to reduce shrinkage and cracking during drying. The raw materials used and the application technique pointed to a well-established construction industry using traditional earthen building materials together with lime technology.