Dry paint layer peeling off (together with one or several layers of paint) due to paint ageing. In the initial stage this problem manifests itself as fine cracks, but later the paint peels off in entire fragments.
Causes:
Low quality paint with insufficient adhesion and ductile properties;
Excessive dilution of paint or applying a layer of paint that is too thin;
Insufficient preparation of the surface (dusty surface);
Failure to prime a deteriorated wooden surface;
Painting in windy weather that causes excessively quick drying of latex paint;
Also see the section on fine cracks.
Solution:
Remove the old paint entirely with a scraper or by polishing. You can speed up work by using a hot air hair-dryer. Then prime the surface with an oil primer and paint with a high-quality outdoor paint.