I have a customer, he bought a flat off of a builder I work for, some damp was found on the top flight of stairs, I expected it to be ingress but could not get next door access, so I hacked off and plastered with dri coat to the top of skirting /stringer . A few months went by, he had some damp spots. I went to look, said its from next door, we got access, the neighbours side was outside and a drain was in the corner, the exterior was pointed but the bottom brick was not pointed along the ground and was soaking water in,I agreed to point this in to weather it, I removed skirtings next door, hacked off down to stringer, bricks were soaked, I said it may take months or years for it to fully dry, recommended leaving the plaster off, he put a heater on this area, went back at his request a few times, he said it drys,gets wet, so on, I said I can tank it, ka tanking or vandex,then dri coat and skim, he is super paranoid, wants me back again to discuss it this week, thankfully the basement I sika tanked is bone dry.