I've had a problem with my gable end wall - the render had blown in quite a few places, so I'm having it all stripped off and re-rendered. I have been told that the problem may well have been caused by the application of too many coats of masonry paint over the years, which effectively sealed the wall, and prevented any internal moisture from evaporating.
Would it be worthwhile installing one or more ventilation bricks at high level to help disperse any moisture that may collect in the cavity?.