Although many old walls have been coated with cement render over the last fifty to eighty years, this is extremely poor building practice on walls made of natural stone. The hardness of the cement does not allow flexibility for the natural movement which occurs in such walls. It also does not have sufficient permeability to allow moisture which is contained within the walls to evaporate through to the surface. Thus the situation arises where the render cracks and de-bonds. In addition, trapped moisture tends to pass through to the inside wall surfaces, creating additional damp “problems”.
The only practical solution, and one that is best for the building, is to completely remove all of the hard cement render and replace it with a traditional lime render which is more flexible and permeable. This will allow for natural movement and drying out of the walls and will also greatly enhance the cosmetic appearance of the building. Unfortunately, this work can be costly.