Bought a home with an old pool this year. The pool had been replastered about 2 years ago but because of a foot print the owner decided to paint it. The paint has bern chipping off with dark plaster underneath which is unslightly, but today I noticed about a 12" section in the deep end where both paint and plaster had chipped off in a crescent shape, about 1/8" thick, several pieces. Nothing has been dropped there. Am I doing something wrong, i.e water chemistry or is this likely a bad plaster job?