Query: When should I use the epoxy resin/solarez and when the polyester ?
Context: if your surfboard It is made of epoxy with an EPS core, you must use epoxy resin , or an epoxy resin-based repairer. If you use polyester resin on a board with an EPS (polystyrene) core, you will see how the polyester resin melts the core of the board, and you will see a large hole in your board.
If your board is made of polyester, with PU foam (polyurethane), it is preferable to use polyester resin. But it's not bad if you use epoxy resin or an epoxy based repairer, it will work too.