It is not uncommon for historic buildings to have had a cementitious render applied at some stage in the 20th Century, before the impact of breathability was understood. Most traditional buildings are constructed of permeable materials, meaning that moisture can be absorbed and released freely, unlike modern construction methods. This is referred to as breathability. Any impermeable barrier applied to the building will disrupt this.
Cement based renders are harder than lime render alternatives and cannot move like the timber frame will seasonally, leading to cracking, which allows moisture into the underlying fabric. As this render is an impermeable barrier, this can lead to moisture being retained within the historic fabric, and resulting in damage which can become structural if left unaddressed. Cement renders, however, do provide some structural support in lieu of failed timber-framing, so its removal should be done in a considered and careful manner.
We are supportive of the removal of cement renders in favour of traditional, breathable alternatives. You will always need Listed Building Consent to remove cement render.
Please note: If you are unsure as to whether your render is cementitious or lime based, apply white vinegar to a small patch of the render. Lime renders will fizz, whilst cement render is unlikely to react.