It is supposed to bond to plastic. The first time I coated my PVC spray-bar it was chipping off easily, I re coated and haven't had any problems since.
I've also painted the intakes to aquaclear filters.
The research I've done on it shows that the company will no back it up as being aquarium safe.
I've used it on my salt water tanks and haven't had any issues. The key is to do very light coats and many of them. If you put on to much at once it won't cure properly and be mroe prone to chipping off.
I've painted my overflow glass and my plumbing with no issues
Even though it say no sanding, I would personally throughly sand your resin (or PVC in other cases) to give a roughened surface to give the paint something to key onto.
Well, where's the photos??
Was the resin fully cured and repaired, how did you prep the surface before painting, how many coats?? come on, we need info and photos
**Edit** I just seen your photo in your other thread!!
its best to rub the pipe down with acetone or something first before you coat. or do a light sand with a fine grit paper. if you just spray it right on, it will chip in places over time.