Alligatoring: Patterned cracking in the surface of the paint film resembling the regular scales of an alligator.
Application of an extremely hard, rigid coating, like an alkyd enamel, over a more flexible coating, like a latex primer.
Application of a top coat before the undercoat is dry.
Natural aging of oil-based paints as temperatures fluctuate.
The constant expansion and contraction results in a loss of paint film elasticity.
Old paint should be completely removed by scraping and sanding the surface; a heat gun can be used to speed work on large surfaces, but take care to avoid igniting paint or substrate. The surface should be primed with a high quality latex or oil-based primer, then painted with a top quality exterior latex paint.