The role of sea salts in the occurrence of different damage mechanisms and decay patterns on brick masonry

Sea salt damage to porous building materials is a well-known problem not only in regions located near the sea, but also in continental areas. In walls sea salts may stem from different sources: they may penetrate from the ground by rising damp, may be carried by the wind in the form of salt spray, may be due to flooding, occasional or recurrent, or may also be caused by the use of sea water in the preparation of the mortar.
Although accelerated crystallization tests performed in laboratory on building materials usually show that sea salts (sodium chloride) are less harmful to masonry than, for example, sodium sulfate, in reality they may cause serious damage. Different decay patterns of sea salt weathering can be found for different sources and conditions. This is shown for a building, with various sources of sea salts present in the same masonry wall: the church of Domburg, located in a coastal area of Zeeland (The Netherlands). According to the sea salt origin a "rising damp zone" showing brick blistering and a "sea spray zone" affected by powdering of the brick can be identified at different height from the ground level. In the first case the effect of sodium chloride is indirect, as the blistering is a result of catalyst effects of sodium chloride on gypsum formation. In the latter case the effect of sodium chloride is direct, as the powdering of the bricks may be caused to by a combination of crystallization, differential thermal expansion and hydration. The paper reports the investigation of the two damage mechanisms in which several complementary test techniques were applied: moisture and hygroscopic moisture measurenzents, ion chromatography, XRD, petrographical analyses, and mercury porosimetry. All of them have contributed to provide a complete and clear definition of the different decay mechanisms in relation to the sea salts and moisture sources