I have an old Sears 12 foot fiberglass I will restore soon. The previous owner put down a heavy coat of resin at some point. I don't think it was gelcoat. Of course there was no prep work so much of it is just falling off. This layer of "whatever" is pretty thick, 1/8" or so. Is there any stripper product that is safe to use on those areas this stuff has actually adhered to or am I just buying lots of 36 and 50 grit paper?