Lime renders vs cement renders

A modern cement render is incompatible with the construction of most old buildings and can cause or accelerate serious decay. Modern buildings generally depend on an impervious outer layer and cavities to keep out moisture. By contrast, old buildings tend to rely on their permeable nature ('breathability') to allow water absorbed by the fabric to evaporate back out.

The use of an impervious Portland cement render in place of a traditional lime-based covering restricts evaporation. Hairline cracks form due to the mortar being more rigid than the wall. These then draw in water that becomes trapped in the fabric. Timber-framed and earth-constructed buildings, in particular, can suffer major structural damage if moisture builds up behind a cement render.

Inappropriate cement pointing on lime bedded bricks