On historic buildings, the use of impermeable cement render can damage underlying brickwork and lead to damp problems
If your house was built before about 1919, it is likely to be of what is known as traditional construction. That means it has solid walls, made using generally soft, flexible and permeable materials – typically earth, lime or clay mortars and plasters that bind soft bricks, stone or timber. These kinds of buildings don’t incorporate vapour barriers or damp-proof membranes as modern buildings do but manage damp and moisture in a different way, through absorption and evaporation. This is known as breathability.
It is essential that any work you undertake as part of a heritage renovation maintains the breathable performance of the building’s fabric. Most modern materials do not do this because they are designed to restrict moisture movement rather than offer breathability. Incorporating products such as cement, gypsum plaster, vinyl paints, impermeable membranes or vapour-closed insulation risks causing very serious long-term damp problems in period homes, leading to decay and mould growth.