Open a jug of epoxy resin after a cold spell and it might be cloudy, grainy, or have solid crystals at the bottom. It looks ruined, but it usually isn’t. Many epoxy resins can crystallize in storage, much like honey does.
How to recognize it
- The resin (Part A) looks cloudy, milky or sugary, or has solid lumps.
- It usually starts at the bottom or around the cap.
- Storage in the cold or big temperature swings make it more likely.
Crystallization is a physical change, not a chemical one. Once warmed back to clear, the resin generally works normally. Epoxy manufacturers such as WEST SYSTEM cover this in their product literature (WEST SYSTEM instruction manuals).
How to restore it
- Loosen the cap slightly so pressure can escape.
- Warm the closed container in a warm water bath, following the manufacturer’s recommended temperature.
- Stir or swirl as it warms, until all crystals are gone and the resin is clear. Leftover seed crystals can start the process again.
- Let it cool to normal working temperature before mixing. Hot resin shortens pot life and can cause a fast, hot reaction.
Don’t
- Heat it with an open flame or in a microwave.
- Use cloudy, partly crystallized resin. It can mix off-ratio and leave soft, sticky spots.
- Heat the mixed epoxy (resin plus hardener) in the container.
Prevent it
Store resin and hardener sealed, off cold floors, at steady room temperature. Buy quantities you’ll use within the shelf life listed on the product.
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