Try to identify the source of the problem, where possible damp is coming from.
Avoid spending Thousands on Damp-Proofing systems and waterproofing of walls. If the walls are not completely dry, the same problem will re-occur and your plaster will flake again.
Expensive paints are not necessarily the best option for a damp wall, as it is more concentrated and doesn’t allow the wall to “ breathe”. Often less expensive paints are more diluted.