When moisture rises by capillarity or when there is moisture ingress through earth retaining brickwork, soluble salts migrate to the surface of the wall. These salts are hygroscopic, meaning they attract moisture from the atmosphere. When chemical or physical damp courses are installed, the wall plaster may still be contaminated by these salts and the wall surface may not be dry. In these instances, it is essential that the wall plaster is renewed to a specialist specification.
These renders and plasters are specifically designed to allow for a slow continual evaporation of residual moisture from the brickwork, whilst giving a “dry” surface allowing redecoration, using breathable emulsion. Specialist renders consists of 3 parts washed sharp sand, to a 1 part sulphate resisting ordinary Portland cement as a base coat 10mm thick, incorporating a waterproof additive in the gauging mix. subsequent coats of render should be applied using 4 parts of washed sharp sand to 1 part Portland cement without a water proof additive. Thistle multi finish wall plaster is used as finish coat.
It is important to note that these specification renders are used and alternative types of sand, cement, light weight plasters etc. are not acceptable and may result in the wall surface remaining wet or deteriorating badly. Specialist renders have been used for many decades, they are proven to be the most successful method of achieving a surface that can be re decorated, after the initial drying period has been achieved.