If it's completely cured I think you can paint it. It does outgas for some time when freshly applied, but if you wait a couple days you should be OK. Also consider using POR-15, everyone on the board seems to like it.
JB Weld will "gas out" for a long time. It took a year or more for it to bubble under a job I once did and it had cured for over a week. In body work, fiberglass reenforced body filler will hold anything JB will.