While WEST SYSTEM® epoxy has a long shelf life, age will eventually affect its handling characteristics and cured strength. When stored for very long periods, hardeners may turn darker (reddish to purple), become thicker and give off more odor. 105 Resin may lose some clarity and also become slightly thicker. Use extra care when mixing age-thickened products (stir extra thoroughly), and don’t use old epoxy if color or clarity is crucial to your project. Although the cured strength of older epoxy may be adequate for most projects, its a good idea to use epoxy less than a couple years old on critical structural joints.
If you’re ever in doubt about old epoxy, do a pot life test: mix 3 pump strokes of resin with 3 pump strokes of hardener, stir thorough and wait for it to cure. As long as it cures within the time frame listed on the hardener container for the temperature you’re working at, it’s good to go.
If the resin has crystalized, simply warm the container in a water bath and stir to dissolve crystals (as you would do with crystallized honey). Performance will not be affected.