Alligatoring is patterned cracking in the surface of the paint film that resembles the regular scales of an alligator.
What Causes It?
This problem may be caused by applying an extremely hard, rigid coating, like an alkyd enamel, over a more flexible coating, like a latex primer.
Applying the topcoat before the undercoat is dry may also cause alligatoring.
Alternatively, the natural aging of oil-based paints as temperatures fluctuate causes constant expansion and contraction that can result in a loss of paint film elasticity.
How to Solve It
Completely remove the existing oil paint by scraping and sanding the surface. You can use a heat gun to speed up 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.
Note: Images provided by The Rohm & Hass Paint Quality Institute.