Why isn’t my epoxy curing?

It is one of the most common questions: why isn’t my epoxy resin curing? After waiting to finish curing you have noticed sticky resin, soft spots, or runny resin (the worst outcome ever). This is a problem that resin beginners and professionals run into from time to time. When mixing your resin and hardener a chemical reaction occurs. The most common issues are:

1. The resin and hardener not mixed at the correct ratio

Measuring the correct ratio of resin and hardener is crucial. This is the most common error. Always refer to the instructions for the correct ratio.  There will be a difference in your mix ratio depending on whether you are mixing by weight or by volume. Always check what it says on the packaging before you start mixing. Never vary the mixing ratio for any reason. Failure to measure correctly will result in soft or sticky castings. ALWAYS MEASURE!!

2.The resin and hardener not mixed thoroughly enough

You precisely measured the correct ratio, but your resin is still not curing, maybe you have not mixed thoroughly enough. Mix for 3-5 minutes or until there are no streaks left in the resin (5-10 minutes in winter). This can fell quite a long time; however, it is important to do this thoroughly and make sure you scrape the sides and the bottom of the mixing container. To eliminate the risk of soft spots pour you mixed resin into a new cup and stir for another 20-30 seconds. This eliminates the risk of unmixed resin from the sides or bottom of the first cup from causing soft spots (Please do it!! It is free insurance)

Never scrape the mixing container while pouring!!! If any unmixed resin or hardener stuck to the mixing container gets scraped out onto your project, you will end up with soft wet spots.

3.Temperature and moisture

The ideal temperature for the curing process is 25°C. The cold temperature will affect the curing process.  Resin/Hardener bottles should feel slightly warm to the touch, if they feel cool, they must be warmed by placing them in warm tap water (NOT HOT!!!) for 5 to 10 minutes prior to use. Never mix hot resin and hardener together! Mixing when cold will often result in cloudy casts containing microscopic bubbles.

4.Too much colourant added

Remember to add a maximum of 6% colourant to your resin. To much colourant can result in a slightly softer cure. (example: 100ml resin + 100ml hardener = 200ml total would require no more than 12ml of colorant. If you are using pigment powders the recommended ratio is 25-50g per litre.

Checklist to Avoid Sticky Resin:

• Measure precisely according to the ratios.  Consult the packaging for specific details
• Mix your resin thoroughly for 3-5 minutes scrapping the sides and bottom of your mixing container as you stir
• Make sure the working environment is around 25-30C or 75-85F
• Don’t add more than 6% colourant to your resin
• Don’t scape when you pour