The most convincing argument comes from chartered surveyor, builder and university lecturer Jeff Howell, in his book 'The Rising Damp Myth' Here Jeff looks at the evidence, and comes to the conclusion that if rising damp exists at all, it is extremely rare, and in most cases the damp is actually due to condensation, or penetrating damp.
Jeff and his university students built walls in water baths to view the effects of rising damp on these walls - but to his surprise, he did not find any evidence of rising damp. Other specialists have repeated the experiments with different types of walls and bricks, and found no evidence of rising damp, either.
Jeff traveled to Holland, to see homes built on wet ground, which remained perfectly dry and damp-free, inspite of not having a vapor barrier.
Jeff and his claims seem to make good sense, from the scientific and observational evidence, but his work has been refuted and discredited by the damp proofing industry.
Explaining How Walls Breathe
It's important to understand this point, as we can then likely explain why you've got damp, and which damp treatments will be effective in preventing damp in the future...
Walls 'breathe air out' as they warm up
Walls 'breathe air in' as they cool down
'Dew point' is the temperature when moisture in the air 'condenses' (turns into liquid water, from water vapor in the air)
water vapor in the air condenses into water droplets and can then cause damp
If the wall 'breathes in' moist air, and then cools, the water 'condenses' as the temperature hits 'dew point'.
If walls can 'breathe' the moisture can leave the wall, as the wall warms up and 'breathes out'.
Any 'seal' on the surface of the wall will trap the water inside the wall, and start to cause problems as moisture builds up, and needs to get out somewhere.
Any natural salts which are in the wall will make the problem worse.
So the solution is to paint with KefaTherm and KefaRid, both are breathable - they actually draws out the damp of the wall. Any other paint claming to be breathable, I would consider to be a modified truth.