This is a question that has probably been asked a 1000 times on here!! I am currently trying to sell a 4 bed detached house built 1901, and unfortunately 3 times a sale has broken down because of the comments of surveyors on damp. When I brought the house 10 yrs ago it had already been treated for damp (holes drilled in outside/inside walls) Our surveyor recommended us to have them re injected, which we did by a new firm (with a 30yr guarantee) In the last 3 months I have had 3 independent surveyors tell me the DPC has failed. I have had the DPC company out several times only to be told that it is a condensation problem. I have tide marks running along inside walls in the hall, 2 walls in the dining room and 2 walls in the lounge. The one internal wall in the lounge, after stripping the wallpaper, has a saturated tied mark rising from the skirting to about 12 inches, the rest of the wall seems dry. The dpc company has now taken a plaster and brick sample to be tested. I don't appear to have any problems above a metre on the walls. Any advice would be appreciated