Why do I have to have the plaster removed when you install a new damp proof course ? It looks sound enough.
Because it is highly likely to contain, as a result of the rising damp, ground salts such as chlorides and nitrates. These are hygroscopic which means that they can absorb moisture from the atmosphere so in cases of high humidity there is continuing internal wall dampness.
Replacing the plaster removes this problem and using a special salt retardant additive in the replastering will prevent any residual salts in the brickwork from migrating into the plaster after the rising damp has been controlled.