Salt crystallization in substitution renders for historical constructions

Abstract eng:
Salt damage is one of the major causes of render decay, not only near the sea but also in continental areas. These salts can appear in the walls from different sources: from the ground due to rising damp, carried by the wind as salt spray, flooding or originally present in materials, like unwashed beach sand or due to the salt transport behaviour of the substrate/render and the surrounding ambience severity (temperature and relative humidity) producing salt crystallization. In this paper an experimental laboratory campaign was developed where perforated red bricks rendered on both sides with four different render compositions and different permeability, were submitted to capillary absorption in a sodium chloride solution. Particular attention was given to the influence of different render solutions when contaminated with NaCl and attention was given to the several dissolution-crystallisation cycles: (a) in the location of sodium chloride crystallization in the specimens; (b) crystallization quantification of different specimens. The final goal is to understand the relation between the more or less permeable renders and the damage mechanisms of NaCl dissolutioncrystallization cycles, in order to propose possible solutions to stop or slow down the salt decay process in walls contaminated subjected to changes in ambient temperature and relative humidity and contaminated with salt.

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