See our page about Breathable Paints
If we are talking about general purpose masonry Paints, for example Sandtex, Weathershield for example. These product are not Breathable and not suitable for a Historic or Old Building.
These types of paint trap moisture and prevent breathability of the walls. They can lead to moisture issues and retention of moisture in the fabric. Quite often we see damp problems caused by these type paints, especially very thick layers applied over years and years. Water inevitably build up behind the coatings and water pressure pushes the paint off the wall. Dulux describe this as;
“Blistering” is the formation of “bubbles” in the exterior decorative paint film, resulting from localised loss of adhesion and subsequent lifting of the existing paint film from the underlying surface. It may be that one paint layer has lost adhesion to the one beneath or it may be that all the paint layers collectively have lost adhesion to the underlying substrate. The loss of adhesion and blistering can quickly lead to paint flaking and peeling.
It is caused by moisture entrapment within the substrate beneath the paint film, which converts from a liquid into a vapour when the surface is heated by the sun and expands but cannot escape through the paint film. ”
So, by Dulux’s technical information really, their paints should probably carry a warning – “NOT SUITABLE FOR ANY PERMEABLE BUILDINGS AKA PRETTY MUCH ANY PRE 1919 BUILDING”.
Internal Paints are covered here….