All solid wall buildings were traditionally built using lime based materials. The introduction of modern cement renders and plasters allows water to enter the stonework but unlike a breathable lime coating, does not allow it to escape. This can result in high levels of moisture within a solid wall. Damp becomes visible, these signs include; areas of black mold, rotting rafters skirtings and windows, crumbling and blown plasterwork.
The only way to remedy damp is to strip out all traces of cement work and re-instate the appropriate lime surface.