Mix some parex Lanko latex up with some dry powder paint it on the wall, leave to dry, mix some more up, paint on, and whilst tacky apply the first pass with what ever your puting on with the mix diluted 30.70 lank water,
Put your top coat on again diluted 20.80 scratch back as normal, with the addition of a couple of weep holes at the bottom using 20mm water pipe, no damp will bridge that.