Epoxies don't have wax in them. But they can develop an amine blush during curing. That needs to be removed before recoating. It is water soluble, so scrubbing with a sponge and water will remove it. You can also lay on a layer of peel ply and when removed after curing, will leave a clean roughened surface. Also an epoxy surface is very hard and can be very smooth, so dope or other products will not stick. Sanding allows a mechanical grip.
Finishing polyester resins do have a wax. Polyester resins will not fully cure in the presence of air (or the moisture in teh air, I forget which). So the finishing resin has a wax that floats to the surface and seals the air out, allowing a full cure. Laminating ployester resins do not have the wax and will have a tacky surface after curing.