If a magnet sticks to it anywhere you have a problem.
You may think I'm only joking but, you would be surprised what has been used by Bubba to repair fiberglass breaks on old Corvettes - license plates, metal mesh, coffee can metal, screws, etc. I have a friend whose 67 Shelby Mustang is being restored and after painting the fiberglass hood just kept coming out bad. Finally the shop ground down into the surface of the hood and guess what - an old license plate used to repair a hole or crack.
