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 laboratory crystallisation tests on building materials usually show that sea salts (NaCl) are less harmful to masonry than, for example, Na2SO4, 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 the church of Domburg, located in a coastal area of Zeeland. 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 heights from ground level. In the first case, the effect of NaCl is indirect, as the blistering is a result of catalyst effects of NaCl on gypsum formation. In the latter case the effect of NaCl is direct, as the powdering of the bricks may be caused by a combination of crystallisation, differential thermal expansion and hydration. The two damage mechanisms were studied using several complementary test techniques: moisture and hygroscopic moisture measurements, ion chromatography, XRD, petrographical analyses and mercury porosimetry. All of them help to provide a complete and clear definition of the different decay mechanisms in relation to the sea salts and moisture sources. 8 refs.
Primary author(s): Lubelli B; van Hees R P J; Groot C J W P
TNO Bouw; Delft,Technical University