You carefully select your resin, mix the two parts together, then pour it in your project only to find the next day that it is sticky or gooey. Sticky resin has got to be one of the worst things ever. It’s incredibly frustrating! No one wants to ask themselves ‘why is my resin sticky?’ There are a few reasons why this could have happened.
Resin and hardener measured inaccurately.
Getting accurate measurements on your resin and hardener aren’t optional, they are essential. The best way you can do that is to use mixing cups with graduated lines to make sure your measurements are as precise as possible. With small mixes, this is even more important! Alternatively, if your resin kit allows it, you can use a digital scale to measure your resin and hardener by weight.
Undermixing resin and hardener.
It’s very important to make sure you mix your resin and hardener together deliberately and thoroughly. This means scraping the sides of your cup and mixing utensil several times during the process.
Pro tip: Ever had a situation where your resin cured but you had a few sticky spots on the surface? You likely mixed the center of your cup well, but the cup edges were not mixed completely. When you scraped out the cup to use that last bit of resin, it did not cure well because it was undermixed.
For extra credit, you can watch my video on how to mix epoxy resin:
The resin and hardener didn’t get warm enough.
Your resin working area needs to be in the low 70’s F (low 20’s C) during the entire mixing and curing time of the resin. It’s also helpful to warm up your resin and hardener bottles in a hot water bath before use. This helps the resin curing reaction to stay at the ideal temperature.
You didn’t mix enough resin and hardener together to allow the chemical reaction to start.
In order for the mixture to cure completely, you must mix together a minimum of the resin component and the hardener component. Put another way, you can’t mix together two drops of resin and two drops of hardener and expect the four drops to completely harden.
Using resin and hardener from two different manufacturers.
Resin and hardener are specifically designed to go together. Unfortunately, one brand’s resin will not likely work with another brand’s hardener.
Water contamination from within the resin.
Depending on what else you used in your resin (colorants, inclusions, etc.) they may have attracted water to your resin mixture. This can also happen when using molds made from alginate.
The resin and hardener mix needs more time to harden.
Double-check the cure time for the resin kit you are using. With any luck, you simply need to give your resin more time to cure.
This is normal for polyester resin castings.
The surface exposed to air during curing will stay sticky, even after a full cure, when using polyester resin.
So, what can you do if you are asking yourself why is my resin sticky?
Here’s how to fix sticky resin.
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