I¹m having a problem repainting an outside workroom in my garden, due to very extensive peeling and flaking of the previous emulsion paint. I¹m quite familiar with all the scraping, sanding and priming of bare spots you have to do to cope with this. However I¹m still finding it a nightmare: every time I think I¹ve scraped off the last bit of unsound paint, sanded, primed (diluted PVC) and applied a new coat, the surface blisters and cracks somewhere else, what looked like sound paint previously.
There seem to be several reasons. First and foremost, it¹s clear the original coat never adhered properly to newly applied plaster (ten years ago), as, by mistake, a primer was not used. When scraping, it¹s very easy to lift the edge of what you thought was sound paint to find that, in fact, it peels away very easily leaving lovely bare smooth plaster beneath. (I try to avoid doing that too much as I don't want to peel away the whole wall, but maybe that's what I should do!)
Next, the workroom has four outside walls, which have no cavity insulation (it¹s converted from anold air-raid shelter). There were some water-penetration problems some years ago, at which time a lot of paint came off inside, but these were all fixed, and paint applied over those bare areas, which were subsequently primed, is now sticking.
My question is this: since this is taking so long to do, and since I¹m have a feeling it¹s all going to start peeling again sometime, would another approach be better. Perhaps strip all the pint and start again. I don¹t want to try that as it sounds an even huger and messier job, but what would be the best way.
Also, the wall don¹t look great because of all the slightly visible edges of so many spots that have peeled and repainted. I¹ve read that Polycell do two products, Base Coat and Smoothover for rough walls: might they help, and could they be used over possible unsound emulsion paint?
Also I've heard about another expensive emulsion paint called Classidur that will cover anything, and, as it doesn¹t stretch when drying, won¹t pull up any loose paint beneath. Would that be any good.
Thanks