Ideally, you should store epoxy resin and hardener in a dry place where the temperature ranges from 60-90°F. In cold weather, store products on a raised surface off of the floor, and don't put any products near outside doors, walls, or windows. Below 60°F, the components can freeze, which is not ideal for the epoxy, especially if it undergoes repeated freeze-thaw cycles.
In addition to freezing, epoxy resin and/or hardener that is stored below the minimum recommended storage temperature can crystallize, making the epoxy appear cloudy and be solid, chunky, or grainy.
The epoxy can still be used - but you have to remove the crystallization first and return the material to its liquid form. To do this, place the container of crystallized material in a warm water bath (maintained at 140-150°F) until the epoxy material inside the container reaches 120 -130°F. If needed, change out the water to keep the temperature at 140-150°F. Stir gently or agitate the container lightly every couple of minutes during the process to break up the crystals.