And thinning epoxy with rubbing alcohol is like pouring some water into the epoxy. Water molecules trapped in epoxy weaken the epoxy structure. And weaken it's adhesion to glass cloth and everything else. The epoxy also winds up curing with pores in it where the water was trapped. When it's trapped inside the epoxy it weakens the structure. When it's near the surface when the epoxy kicks it creates pores. The pores often keep thin epoxy from fuelproofing or waterproofing.

If you're going to thin epoxy, use acetone. It was made to do the job. It's in home improvement stores, hardware stores and paint stores. And it's cheap.

It's cheap and also great to have around when you get CA on Ultracote/Monokote. It wipes it off. And it preps painted surfaces that are going to be decaled or filmed.