Along the surfboard manufacturing process, you will certainly need some chemical additives : wax in styren, monomer styren, PMEK catalyst, UV catalyst, microbaloons, silica, aceton...
Added to your polyester resin, it helps the polymerization step.
There are 2 types of catalyst to choose from: PMEK liquid catalyst (traditional), or a UV catalyst which gives you more time to work, as the polymerization would only start once the board is exposed to sun light.
Glassing additive, accelerator, optical whitener, stratoglass, are main additives which you will use during your epoxy constructions.
The EP 217, while blended with your hot-coat resin, gives a lower viscosity of your resin. This will allow an smoother application of the material and a much easier sanding.