Saw this not long ago and we traced the problem to the color coat. Check the original cans and look at the ingredients. Our problem was with Rustoleum, bought the cans a few weeks apart and the during that time the store had replace "new" paint with the "old". There was a slight difference in the chemical make-up of the paint...lesson learned - Buy more than enough to do the job at one time, you can always return what you don't use!!
Either way we scraped it all off as the alligatoring was sooooo bad. Good Luck
