The materials (bricks and mortar) used to restore the walling were studied in collaboration with the Aristotle University of Thessaloniki as part of the NATO-funded Science for Stability GR – RESTORATION research programme. The purpose of the programme was to conduct a laboratory investigation of the ancient mortar, bricks, and plaster, to develop criteria for selecting new materials compatible with the ancient ones, and to draw up specifications for quality control. The ancient materials were documented on the basis of information given by ancient writers and the experimental results of systematic analysis.
The bricks used to restore the masonry were made by hand and have the same physical and mechanical characteristics as the ancient ones:
— colour, dimensions, and surface morphology
— crushing strength, porosity, low moisture absorption by capillary uptake.
Suitable types of clay, with a low proportion of phyllosilicates, were selected in collaboration with the manufacturer, and aerating admixtures were also used.
Modern method of manufacturing handmade bricks
Brick-making techniques were fairly simple and do not seem to have changed much until they were industrialised at the end of the 19th century. The stage in the process were : extracting the clay, maturing the clay (dissolving the salts it contained), shaping or cutting the bricks, drying, and firing.
The composition of the new types of mortar that were produced from an admixture of such traditional materials as sand, lime, pozzolana, crushed tile, and tile-dust was based on the proportions of the original materials as determined by laboratory analyses of the ancient mortar. The new mortar is of three types, corresponding to the ancient types, and the appropriate mortar was used in each building.