chapter  33
13 Pages

HYGROSCOPIC SALTS—INFLUENCE ON THE MOISTURE BEHAVIOUR OF STRUCTURAL ELEMENTS

In the repair and conservation of masonry structures the protection of building elements against moisture is of particular importance because most types of degradation of materials such as natural stones, clay bricks, mortars and plasters occur in the presence of moisture. Aside from rain, in many cases excess moisture is absorbed by the foundations of the building due to capillary rise of water. Then, soluble salts may be transported into the pore system of the building materials by capillary flow. Despite of the fact that normally the adsorption of moisture from the atmosphere results in a low moisture content, a drastic increase of moisture concentration can be observed due to the hygroscopic effects if the material is contaminated with soluble salts. At the evaporation zone these salts may cause damage mechanisms like efflorescence and salt crystallization depending on the temperature and the relative humidity of the ambient air.