This is a lesson on reading the instructions. Artex on the ceiling of bathroom was cleaned before painting with bathroom paint. It all peeled into flakes when dry. Reread the instructions which said, if porous surface, paint with 1 part water, 10 parts paint. Oops. Removed the paint, which with the scraper, also removed artex and we were back to plasterboard. Applied the paint in the ratio described which looked fine. After drying overnight and it still looking fine, reapplied a second normal coat. 90% is fine but there are more patches of flaking paint. Lesson learnt. But now what? Embarrassed. Thanks.