What is an epoxy finishing resin?
It's an epoxy that cures to a harder surface that is easy to sand. It's usually to brittle use in fiberglass cloth. You'd use regular epoxy to build the fiberglass part then finishing resin for a easily sanded filler coat. Like other have said regular epoxy is kind of elastic so it can be a pain to sand.
I see. I've just never heard the term before when refering to an epoxy laminating resin. It seems like a throw back to polyester. When a polyester resin cures it cures with tacky surface when exposed to ambient air, though the resin just below the surface has cured nice and hard. Additional layers can just be added directly to this tacky surface and still get a good bond. When one wants a final layer that isn't tacky, wax is added to the polyester. The wax migrates to the surface of the resin and creates a seal to the abient air. This causes the resin to cure with a hard surface. The wax needs to be sanded an cleaned away if any painting or bonding needs to happen. Polyester that comes prepackaged with wax is called a finishing resin.
Is the "regular stuff" like a 30 minute bonding resin? That sounds like agony to use.
I've used MGS L285, Resin Research 2070, US Composites 635, MAS, Adtech 820, and Proset epoxy. These are all true laminating epoxy resins. They are used to laminate fiber reinforcements and they still sand to a white dustly powder.