Checking is a pattern of breaks in the top layer of a coating.Cracking and flaking are advanced stages of checking. Checking results when a coating begins to lose its elasticity, developing small narrow breaks due to expansion and contraction. These breaks are on the surface and do not penetrate to the substrate. They usually follow the pattern of the grain. Further exposure will result in wider breaks or cracks in the coating that eventually reach the substrate. As time goes on, the coatings begin to flake off.
Remedy:
Remove as much loose paint as possible.
Use an exterior speckling compound to level uneven areas.
If many layers are involved, remove right down to bare wood.
Prime all bare wood with exterior primer.
Cracking down to the substrate usually means complete removal of the existing coatings.
Apply a flexible topcoating such as water-based acrylic.