Weathering traces in ancient bricks from historical buildings

Abstract

The aim of this work was to determine the type of weathering suffered by bricks belonging to a number of historic buildings in Toledo, Spain. These bricks had been exposed to either aerial or burial environments, came from different places in the selected buildings, were of different mineralogical composition, and had been fired at different temperatures. X-ray diffraction, scanning electron microscopy and the analysis of their physical properties showed the best conserved to be those that had been buried. Buried Roman bricks made from non-calcareous materials fired at >900°C and with a vitrified matrix showed few signs of weathering. Buried Islamic and Mudejar-Romanesque bricks made from calcareous clays and fired at temperatures of <800°C were similarly well conserved. These showed calcareous cementation of their pore systems, which improved their physical properties. Bricks from the external and internal walls of buildings (e.g., Islamic–Mudejar and Romanesque bricks from inner courtyards and cellars) that had been exposed to aerial conditions were less well conserved. These were made from calcareous materials and had been fired at high temperatures (> 900°C). They showed a number of weathering traces but overall were still in relatively good condition. The worst conserved of all were neoclassical bricks from upper storey internal walls. These were made of calcareous material and had been fired at temperatures of between 800 and 900°C.

The mineralogical composition of the raw materials, the firing temperature, the location of the bricks in the buildings, the environments to which they had been exposed, the action of natural or polluted filtration water, the action of microorganisms and the reigning environmental conditions, all contributed towards the state of conservation of the bricks. Such knowledge may help in the choice of appropriate cleaning or restoration treatments for architectural heritage of brick construction.