I am renovating an old cottage with original walls built with stones and mud with a cement finish inside and out. My problem is the interior paint turns to powder after a few months and falls off the wall, this happens on the lower part of some walls and only in some areas. We checked for damp, water ingress etc. and it happens on walls to the outside and interior dividing walls.

The cycle is paint with an interior matt water-base white paint, after a few days a few surface bubbles, but not everywhere, and then later the paint “grows” white dry fur of between 2 to 5 mm high and turns to powder so you can brush it off the walls. Sealers, undercoats etc. do not help much, they only delay it by a few days and I am beginning to suspect a chemical reaction from the walls.

There is no damp or any kind of mold on the walls, it just seems to react and dry the paint to powder. Acrylic white paint does the same thing!
Any advice or help would be appreciated.