The thickness of your epoxy determines the thickness of your coating. A fluid epoxy will form a thin surface, but even a 4 to 6 mil coating can achieve excellent abrasion resistance. Insufficient thickness can nonetheless reduce performance. If your surface is going to be exposed to petroleum products or heavy abrasion, you will probably need a much thicker layer of epoxy. Viscosity alone cannot achieve the right protection. The use of diluents can thin your coating, ultimately leading to cracking and pinpoint rusting.