The resin is pretty thick, but shouldnt be goopy or have any types of clumps. The consistency of fiberglass is like honey or pancake syrup. Usually if its the bondo brand resin and has white streaks in it as I pour it into a mixing pan, I toss it. Fiberglass resin does get old. Also avoid shaking the resin, it creates bubbles, stir it instead.

The consistency could also depend on the room temp and storage conditions as well. Remember resin is a hazardous material, so make sure to avoid skin contact and breathing the vapors, use plastic sheeting or a tarp in your work area if you are concerned about a mess.