Actually I think it's called 'old government built house with solid walls'.
As has been said, find the problem and treat that. Don't attempt to treat the symptom, it won't work.
Most houses with solid walls relied on a layer of waterproof mortar called 'rendering' to prevent water wicking into the house. It needs to be in good condition.
After quite a few decades it probably won't be, so it may need to be repaired or replaced.
Roof coverings, guttering, downpipes, back-inlet gullies, drains and any soakaways need to be inspected and if necessary maintained.
Openings such as windows, doors and vents will all have some means of waterproofing, these will also need to be inspected and maintained if necessary.
Welcome to the private sector!