Hello Freddie, I've used, Zinnser, then tried Dulux water blocker, then three coats of oil based undercoat. Each time, about two weeks later blisters appear. I've left adequate time between coats. Can't find where the water is getting in, hense need something extreme to block it coming through and blistering the paint. I've asked various decorating suppliers, who suggested the products I've used.
I'm hoping someone has had this issue and cured it with something other than the usual. I've used lighthouse masonry paint on a house where the owner has previously used many trade quality products, he kept getting peelage after 6 months (north Wales). Lighthouse paint has been a success. Thinking outside of the box solved that one.