Efflorescence

Water-soluble salts (calcium nitrate/saltpetre, calcium sulphate, sodium carbonate, calcium carbonate, etc.) in mineral building materials are transported to the outside, the water evaporates on the surface leaving the salts in the form of crystalline deposits. These salt crusts affect the visual appearance, especially of dark surfaces. Surface damages (cracks) or a lacking connection between substrate (concrete, masonry) and covering (voids under the plaster/render) may lead to spalling as salts forming crystals have a larger volume than solved in water. Washouts of water-soluble salts can only take place in the presence of water, a perfect ratio as well as sealing against rising damp and rain water are examples of appropriate remedial measures.