Dampness in historic properties is often caused by inappropriate material choice, frequently plaster. Using modern (gypsum) plasters, renovating plasters etc results in the absorption of moisture, prevents its release/evaporation and can accentuate and increase issues of dampness penetration and rising dampness - yes, contrary to a number of deniers, rising dampness does exist, albeit less frequently than often thought! - back to the issue!
Removal of the modern plaster, allowing structure (timber, stone, brick or cob) to dry out and if necessarily, replacing it with a lime (air lime - putty - or if absolutely necessary, a weak hydraulic lime) is likely to work wonders.
