I've had an on and off problem with damp and need some advice. On my exterior wall near my air brick I seem to have damp coming through. This seems to be the start on the damp, it's at the bottom in the corner, but it has spread across both walls according to readings. The paint and plaster is coming off in the corner. The damp course has only been reinfected a few years ago, someone did look at it and say it maybe surface water, anyone any ideas on how to deal with surface water damp?