Selection of plasters and renders for salt laden masonry substrates

The choice of a repair plaster or render by architects often appears to be the result of fortuitous circumstances, such as prior experience with a plaster or a recommendation by a producer. Seldom is the choice based on a sound assessment of the state of the building and the wall that is to be repaired. The service life of the repair plaster/render (and of the building to be conserved) is determined by many factors. In this paper, the most important factors affecting the risk of damage caused by salt are discussed, taking into account both the service life of the repair plaster/render and the conservation requirements of the existing building. The characteristics and performance of the various types of mortar for repair plaster or render are also reviewed. Next an attempt is made to evaluate the significance of the different factors affecting the choice of mortar. Then, taking into account the degree of risk of damage and performance data of the various types of repair mortar, possible mortar choices can be made for a repair plaster with an adequate service life. The final choice will depend on the specific conservation requirements for the existing building fabric.