Damp in walls

[Brian Meliot]

About 5 years ago I had a new DPC injected with the plaster renewed on the inside up to the required height. During the last few months a horizontal area of dampness has appeared above the new plaster in the hall and extending upwards about 12 inches - although this does vary. I have checked the outside render for cracks but can see none that are obvious - save for one area where I have chipped it out and made good. The house itself was built in 1929 and masonry paint has been applied a number of times over that period. I am in the process of removing the inside plaster where it is damp and intend removing the masonry paint on the corresponding area on the outside to check whether there are any cracks that I cannot see. I believe (but am not sure) that I may have applied a PVA adhesive coating over the offending area (on the outside) at some time after the DPC was injected. does anyone have any ideas as to the cause and the remedy?