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Nabatean mortars - technology and application

Deliverables

The results of the project have been presented to the concerned institutions, architects, engineers, representatives of the industry and site owners by two workshops in Amman and Damascus. The Damascus workshop has been organized with another EC project (PRODOMEA) under the topic “Compatibility and Mortars: Conservation Approaches for Archaeological Sites in the Mediterranean Area” in an international frame. The practical aspects of the results like mortar preparation and application, the use of on-site tests and the application of consolidants and poultices have been demonstrated to engineers, local workers and local representatives of the cultural heritage administration by two practical workshops in Petra and Bosra.
A repair material which is most probably suitable was proposed for each of the most important conservative needs at Qasr al Bint (adhesion/repair mortar, sacrificial plaster, grouting mortar). Each of the formulas was tested in the laboratory, in the field and by on-site application. In Bosra the traditional hemp fibre mortar was improved with regard to workability. Moreover a guideline was developed of how to adjust the particle size distribution of the aggregate in order to minimize the formation of plaster cracks. The results are useful for a conservation of the mortars, plasters and the stucco at Qasr al Bint and for any conservation of historical plasters by materials similar to the historical ones in Bosra and Syria. The end-users of the results comprise concerned public institutions, architects and engineers.
Dependant on the function of the mortar the Nabateans used various kinds of binding media (gypsum and/or lime) at Qasr al Bint and various kinds of aggregates and admixtures (limestone, basalt, pumice, fibres) at the Great Cathedral in Bosra. This gives a detailed impression of the advanced building technology in Nabatean times. Soluble salts transported into the wall by rising damp or by wind deposit are the most severe threats to these ancient materials. At Qasr al Bint the problem is increased by the partial dissolution of historical gypsum mortars and their recrystallization within the adjacent building stone. The mapping and testing campaign provides spatial information of the various materials and of the damages at the building. This information can be used by archaeologists e.g. to discern various construction periods and by the concerned institutions and/or restorers as a pre-information for the formulation of a preservation concept.