Hydrophobic treatments and their application with internal wall insulation

Hydrophobic (or water repellent) treatments have been proposed to mitigate moisture risks associated with internal wall insulation when applied to solid masonry walls. This can reduce risks associated with moisture accumulation within the structure such as mould growth or the deterioration of joist ends and other embedded timber. Where treatments perform well there is a net reduction of moisture content and risk. However, such treatments slow down drying processes, and therefore may result in a net increase in moisture if the treatment is bypassed by, for example, cracks. Some treatments may lead to damage to external masonry surfaces in some situations. Freeze-thaw and salt crystallisation are the two main causes. Hygrothermal simulations may give some indication of risks but techniques to assess the risk of surface damage are either simplistic, impractical outside of the research environment or both. This paper reviews the current field of assessing and predicting the risk of surface damage associated with surface treatments.