For coating applications, an epoxy resin systems can be thinned with solvents such as lacquer thinner, or denatured alcohol for better brushability. In most cases, adding 1-3% solvent to a mixed batch of epoxy is all that's required. Never thin adhesives as the bond strength can be compromised. Additionally, thinning epoxy with solvent is not a good idea when wetting out fiberglass cloth.
A different technique to lower the viscosity of adhesives and epoxy resins without adding solvent is to bring the base temperature of both components up to 80-90F. The viscosity of epoxy can be reduced significantly when heated into this range. Keep in mind when heating epoxy that the pot life of the mixed material will shorten fairly dramatically. The shortened pot life can be managed by mixing batches small.