THE IMPACT OF PLASTERING ON THE HYGROTHERMAL BEHAVIOUR OF HISTORICAL SANDSTONE LOCATED IN THE COASTAL REGION OF LEBANON

Abstract

In an unusual trend in the conservation practice of built heritage in Lebanon, the external plaster layer, which protects the sandstone from weathering factors, is being removed for aesthetic reasons. These buildings are in a coastal region, hot humid climate in the summer and moderate cold weather in the winter. This paper discusses the importance of external and internal plastering of the historical sandstone bearing wall, by the mean of a computational tool that underlines the role of the plastering in the hygrothermal behaviour of the historical stone, in the aim to validate the practice of the ancestors in covering the envelope of their buildings to avoid the degradation of these natural stones. The methodology adopted in this paper is a comparative quantitative study, using a hygrothermal simulation modelling tool, named Wufi Pro, which is a standard program for evaluating moisture conditions in building envelopes developed by the Fraunhofer Institute for Building Physics (IBP) Stuttgart, Germany. The results are in the form of values for the heat and moisture fluxes through the high porosity sandstone assembly that composes the building envelope. These values represent the hygrothermal behaviour of the stone, and they are compared between two cases, one without plastering while the second has the inner and outer layers of traditional plaster. The analysis of the results is guiding to a conclusion that favours one of the two cases, taking into consideration the interstitial condensation threat avoided by the means of plastering.