Modern render mixes tend to be incompatible with the construction of most older buildings and can cause or accelerate serious decay.
Modern buildings generally depend on an impervious outer layer and cavities to keep out rainwater ingress. By contrast, old buildings tend to rely on their permeable nature (‘breathability’) to allow water absorbed by the fabric to evaporate back out when weather conditions allow.
The use of an impervious Portland cement render in place of the traditional lime-based mix restricts evaporation.
Hairline cracks form due to the mortar being more rigid than the wall. These will draw in water that becomes trapped behind the render.
Loss of key will undoubtedly follow with major sometimes dangerous structural damage.
Alternatively you could invest in total preservation of your most valuable asset Andura resin bonded decorative and protective exterior waterproof coatings have been specified for masonry type walling subject to harsh climatic conditions throughout the UK over a period of thirty-five years with guaranteed proof of performance. Available in a range of heritage pastel shades and brilliant white.
Perlite Thermal Insulation is now available as an added ingredient for homes with solid wall construction. Consisting of millions of hollow ceramic vacuum segments, each no larger than a grain of sand, it enables the exterior fabric to preserve heat like a thermos flask. Warmer in the winter and cooler in the summer plus a considerable saving on the energy bill.