How to repair damp damaged walls.

Inappropriate use of materials is almost certain to be the problem. Cement and modern gypsum are not vapour permeable, hence the reason we use lime plasters and renders for our restoration work in older properties and appropriate paints. As its lower level damp it could be caused by rising damp as capillary action will only allow damp to rise to a height of just over a metre, anything higher up could be ingress, another place to look would be at the drainage near the external wall, so often people lay concrete up against the wall, have raised flower beds, ideal thing is a french drain to allow surface water to drain away effectively. This said, it can be difficult to pin point with out looking at the property to evaluate things properly.

before you do repair from inside like plastering you have to find the main reason why that happened by professional, then solve the problem from outside, then plastering inside, then damp proofing paint, then undercoat and finally main paint at least two time. good luck

Remove all cement based render and any gypsum based plaster. Render and plaster using Lime based material in both cases and only use washed river sand.Leave the internal plaster free from the floor by at least a couple of inches, more if your skirting allows. Only paint, internally and externally with breathable paints, preferably lime based. In all cases, try to think as the original builder would have done, then try and match as closely as possible. Good luck!