Why doesn't my epoxy harden?

It is possible that your epoxy has not (completely) hardened. In this article we list common causes why epoxy casting resin sometimes does not harden properly and what you can do to prevent this.

why doesn't my epoxy harden?

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

1. Epoxy not mixed properly

Epoxy consists of two components that must be thoroughly mixed for the proper curing process. If the components are not mixed properly, your epoxy will not cure (completely). You will need to mix the two component epoxy for at least 5 minutes, making sure to scrape the sides and bottom of the container. Only stir in one direction, otherwise many air bubbles will be created 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 , you mix this resin 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 product packaging. Never add hardener again to influence the curing time. The epoxy will then not harden properly. If epoxy is mixed correctly it will almost always harden.

3. You used too much pigment

Pigments for epoxy casting resin such as paste, powder and colorant 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. For example , pigment paste for epoxy contains a small amount of epoxy. So you can't just use any random 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. Consult 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, for example in a bain-marie, before mixing them to accelerate 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 affects the mixing ratio. This can cause the epoxy to remain soft and sticky or not even 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're using 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.


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

If the above tips from our epoxy experts were perhaps one of the causes, you can try again.

If there is not (fully) hardened epoxy stuck in your silicone mold, you can place it in the freezer for 30-60 minutes. This does no harm and ensures that the epoxy hardens properly and then releases from the mold. Always do this wearing nitrile gloves to protect your hands. When the (failed) epoxy has hardened in the freezer, you can remove it from the mold. Immediately throw it away in a garbage bag, because it will immediately thaw again and become liquid.

Additional tips for mixing epoxy:

  • Use an epoxy stirring spatula to mix the two components well and thus prevent air bubbles.
  • Always use an epoxy scale that weighs accurately to 0.1 gram.
  • Pour the epoxy slowly into the mold or onto the object to prevent air bubbles from forming.
  • If your epoxy has not hardened properly, you can apply an extra layer on top of this layer.
  • Allow the resin to harden for at least 24 hours before applying additional coats.
  • It can happen that epoxy crystallizes. Heat the epoxy in the closed bottle in a bain marie at 60 degrees. Then shake the closed package of warm epoxy well and you can use the epoxy again afterwards. If any crystals remain, the resin will be crystallized again in no time.

More information?

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

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


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