Mortars and Stones of the Damascus Citadel (Syria)

Abstract

Some buildings of the Damascus Citadel (Tower 12, Tower 8, Ayyubid Hall, and a neighboring building) have been investigated in the frame of the Italian Home Ministry collaboration and a Syrian Italian Cooperation Project. The petrography, mineralogy, and chemistry of several joint and repair mortars and stones and their degradation conditions were investigated with the aim of collecting information before planning conservative interventions. The following techniques were used in the study: X-ray powder diffraction, optical microscopy, scanning electron microscopy associated with energy dispersive system microanalysis, and inductively coupled plasma optical emission spectroscopy (ICP) for chemical analysis. Different types of mortars, which were used in different times, have been identified on the basis of their mineral constituents and relative amounts: 1) gypsum; 2) quartz, calcite, and gypsum, in decreasing amounts; 3) quartz and calcite, both in high amounts; 4) calcite and subordinate quartz; and 5) calcite with very low content of quartz. Mortars suffered variable degradation (mostly powdering), depending on their original composition. All the rocks used during the building of the Citadel (fine-grained carbonate, cherty carbonate, nodular carbonate, and carbonate breccias, subordinately basalts), extracted in areas not far from Damascus. The stone surface presents powder deposits, concretions and black crusts. They suffer different kind of decay: erosion, cracking, surface flaking, dissolution, biodeterioration (vegetation and guano), and, more rarely, sulfation. Mineral dissolution–deposition processes generated stone surface deposits of calcium carbonate and, rarely, halite, carbonate, and niter.