Why doesn't my epoxy harden?

It can happen that epoxy is not (fully) cured. In this article we name common causes why epoxy casting resin sometimes does not cure properly and what you can do to prevent this.

If your epoxy casting resin does not harden (properly), this may be due to a number of causes:

1. Epoxy not mixed properly

Epoxy casting resin consists of two components that must be thoroughly mixed for the correct curing process. If the components are not mixed properly, your epoxy will not cure (completely). You must mix the two components of epoxy for at least 5 minutes, making sure to scrape the sides and bottom of the container. Stir in one direction only, otherwise there will be a lot of air bubbles in the epoxy.

2. Incorrect mixing ratio

The correct ratio between the two components is crucial for the curing process. The easiest resin available is the Epoxy casting resin 1:1 , this epoxy is mixed 1 to 1 gram. Most types of epoxy are mixed 1:6 or 1:5. If the ratio is not correct, the epoxy will not cure. Always mix the components accurately by weight or volume according to the mixing ratio stated on the packaging of the product. Never add more hardener to influence the curing time. The epoxy will then not cure properly. If epoxy is mixed correctly, it will almost always cure.

3. You used too much pigment

Pigment for epoxy casting resin such as paste, powder and dye can give a beautiful look to your project. But if you use too much pigment your epoxy can sometimes not harden properly or remain soft. The packaging of the pigment, powder or dye states how much you can use.

Always use real pigments for epoxy , because they are specially made for this. Pigment paste, for example, contains a small amount of epoxy. So you can't just use any paint.

4. Wrong temperature

Epoxy cures best at room temperature. If the temperature is too low or too high, the curing process can be slowed down or stopped altogether. Refer to the label on the product for the correct temperature. Usually this is (15-21°C).

If the ambient temperature is lower, you can try heating the resin and hardener in a bain-marie before mixing them to speed up the epoxy curing.

5. Humidity too high

If there is a lot of moisture in the air, this can lead to incomplete curing or even soft spots in the final product. Moisture (and therefore water) negatively influences the mixing ratio. This can cause the epoxy to remain soft and sticky or even not adhere.

Make sure you work in a dry environment and that your workplace is well ventilated. Do not work in high humidity above 55%+. An epoxy that is 'vandal-proof' and can withstand different air conditions is the UltraEpoxy .

6. You use old epoxy

Epoxy has a long shelf life of at least 2 years. If the epoxy is old or has been exposed to certain temperatures, it may not harden properly. Check the manufacturer's instructions. Always store the epoxy in a dry, safe place at room temperature.

Conclusion

Working with epoxy is incredibly fun and relaxing to do, but like any hobby it requires some experience. Once you get the hang of it, it is a great and versatile hobby.

If the above tips from our epoxy experts may have been one of the causes, you can try again.

If there is not (fully) cured epoxy stuck in your silicone mold, you can put it in the freezer for 30-60 minutes. This will not do any harm and ensures that the epoxy hardens properly and then comes off the mold. Always do this with nitrile gloves on to protect your hands. When the (failed) epoxy has hardened in the freezer, you can remove it from the mold. Then throw it away immediately in a garbage bag, because it will immediately thaw and become liquid again.

Additional tips for mixing epoxy:

• Use a stirring spatula to mix the two components well and thus also avoid air bubbles.
• Always use a good scale that weighs accurately to 0.1 gram.
• Pour the epoxy slowly into the mold or onto the object to avoid creating air bubbles.
• If your epoxy has not cured properly, you can apply an extra layer on top of this layer.
• Allow the resin to cure for at least 24 hours before applying additional coats.
• It can happen that epoxy crystallizes. Heat the epoxy in the closed bottle au bain marie at 60 degrees. Then shake well with the closed packaging warm epoxy and you can use the epoxy again afterwards. If crystals remain, the resin will be crystallized again.

More information?

Do you have questions about making art, jewelry or casting/coating floors or other objects? At itsOkay, several epoxy experts work with each their own expertise. We are happy to help you.

Please contact itsOkay customer service or take a look at the Epoxy knowledge center .