Damp is not one problem, it is three, and each needs a completely different fix. Treating the wrong type is the most common reason damp keeps coming back, so it is worth understanding the difference.
Rising damp comes up from the ground through the wall. It usually shows as a tide mark up to about a metre high, often with damaged plaster or peeling paint near the skirting. It is caused by a failed or missing damp proof course and needs proper treatment at the wall, not just redecoration.
Penetrating damp comes in from the outside through a defect: cracked render, failed pointing, a roof or flashing fault, or a gap around a window. It tends to appear as a patch that gets worse when it rains. Fix the external defect and the internal patch dries out.
Condensation is moisture from inside the home, from cooking, washing and drying, settling on cold surfaces. It shows up as black mould in corners, around windows and in poorly ventilated rooms like bathrooms. The answer is better ventilation and moisture control rather than treating the wall itself.
Because they look similar but need opposite solutions, a proper inspection matters. We test and assess before recommending anything, so you only pay for the treatment your home actually needs.