Epoxy resin artists, enthusiasts, and hobbyists will all run into issues whether you are experienced or just starting out. Almost all of these issues happen during prep, pour, and cure. One of the most common is an end product, made of epoxy resin, that is soft and flexible. Thankfully (or unfortunately) there are many diagnoses to this issue.
The main reasons your epoxy resin is flexible and soft boil down to not enough curing time, improper ratios of base resin and hardener, not mixing well, pouring too thin, expired or compromised resin, and moisture in your epoxy prior to cure- resulting in an epoxy resin that rubbery and flexible.
Thankfully, most of these issues can be avoided with proper understanding. Whether you are an amateur or seasoned veteran who is, for some reason, dealing with this issue, there are several solutions at hand. Below, I have broken down the six most common scenarios for flexible epoxy, as well as reasons why each one may have affected your pour.
1 – Resin is Not Fully Curing
Hands-down, the resin not fully curing is the most common reason I see epoxy resin not hardening properly. While many containers or other artists will tell you that in 24hrs (for example) it will be hard enough to demould or sand, this is not always the case. Many resins need a lot more time to cure than just the minimum.
Truly, this can be so frustrating as you await the completion of this step in your epoxy resin project, but it is essential to get right for a fully hardened epoxy coat. There are a lot of factors that go into how long you should wait for your epoxy resin to cure, but here are the two primary factors:
The Brand of Epoxy
Different brands of epoxy will have different cure times. This is all up to the chemical amounts and ratios within the specific epoxy you are using. There is also an issue of pour depth and viscosity of the epoxy resin, which can contribute to resin not curing.
You will find that high-quality versus low-quality epoxy resin can be highly distinguishable in its cure time, notably based on the viscosity and pour depth. Be sure to check the description (as well as any available reviews) before opting for a particular brand- especially if it is a remarkably cheap one.
Temperature is Cold
The air temperature, epoxy temperature, and mold temperature all play a factor in the cure-time of epoxy resin. The way epoxy hardens is by an exothermic reaction. If the temperature is colder on any of these factors surrounding the epoxy resin, it can slow down a cure.
Because of this, you will need to make sure to work in a controlled atmosphere when working with epoxy resin. Check the temperature recommendations on your specific brand of epoxy resin, but note that ideal temperatures typically range from 65-80 degrees Fahrenheit (although this varies based on the brand).
2 – Wrong Ratio of Base Resin and Hardener
Another common mistake a lot of artists (new and experienced) make is an improper ratio of the two parts of epoxy resin. For many brands, this ratio will be a 1:1 ratio by volume. Other brands will have a weight-based system for calculating the appropriate amounts of resin. While neither is better than the other, both allow for a margin of error, particularly on small pours, that could be lethal to your epoxy pour.
For this reason, among others, it is important to take a closer look at the recommendations based on the particular brand of epoxy that you are working with. This can be one reason that experienced resin artists can get into this tricky issue- they are using an epoxy that is new to them that has a different ratio than what they typically work with.
Regardless of your level of experience, be sure to use the right ratio of base resin and hardener to achieve a hardened epoxy instead of a flexible, soft mess.
3 – Not Stirring Long Enough
Hand-in-hand with the wrong ratio of base resin to hardener is the issue of not stirring your epoxy resin long enough. This is a mistake many people make, particularly when you do not use a timer. It can become tiresome if you are mixing your resin by hand, especially when it needs to be mixed for 5 minutes.
Oftentimes the mistake is to see the color that you have added having taken over the entire container, and assuming that means it has been fully mixed. In reality, the full mixing of chemicals takes much longer than just the pigment mixing in and providing a strong visual appeal.
Pro tip for stirring epoxy: If you are doing a small pour, the edges are most likely to be mixed poorly. Avoid scraping the edges of the cup, or transfer from one mixing container to another before pouring to help minimize risk.
4 – Epoxy Resin Pour is Too Thin
Alluded to in the first possible reason, epoxy resins are crafted specifically to pour at different depths. If you are pouring a coaster, for example, but using epoxy that is made to pour at a thicker level (commonly 1-3 inches depending on the brand), then you can expect the epoxy not to harden as you expect.
Instead, using an epoxy resin pour that is too thin will almost always result in a flexible and soft epoxy resin, as it never gets hot enough to have a proper exothermic reaction. To avoid this issue, you want to make sure that you are using a high-quality epoxy resin specifically designed for the depth of pour that you are intending to make.
Of course, it can be frustrating to continuously have to buy new epoxy, but when you use the appropriate epoxy resin for the projects you have in mind, you avoid costly mistakes. Then, you have a nice supply of epoxy ready to go for the next project you have in mind.
5 – Resin Might be Too Old
Usually, it is easy to tell when resin has expired. The first clue is an expiration date, though these are not always accurate to the true shelf-life. A good way to know if your resin might be too old is if the epoxy resin parts are turning yellow in their respective containers.
Expired or compromised resin is going to differ on how it causes issues, but one of the most common is with rubbery-resin after curing. This is due to the chemicals being weakened over time, especially if the resin is not kept in a cool, dark, dry, area. Moisture and sunlight are common culprits of ruining epoxy resin before it gets used.
Unfortunately, there is little you can do once your epoxy resin has expired. However, if you are experiencing this, you can learn from your mistakes and be sure to properly store your epoxy based on the specific recommendations on the option you choose for your next project. Then, you should be able to experience hardened epoxy in no time.
6 – Resin Could be Retaining Moisture
Epoxy resin, particularly in small doses, is prone to being compromised. There are a lot of reasons moisture is in your epoxy resin. And, of course, resin that is retaining moisture will remain flexible and soft rather than hardening for a completed project. Here are the most common reasons moisture might be in your epoxy resin:
- Liquid pigment. The top reason moisture might be in the epoxy resin is from a liquid pigment. If you are going heavy on the liquid pigment, you are likely to run into this issue on smaller batches.
- Pouring in a damp location. Another reason, which hopefully you have considered, is pouring in a damp location. If your basement or garage is not kept dry, you are likely to have moisture in the air which can ruin a cure.
- Moisture in the container. Moisture may have gotten into the container of resin or hardener due to where it was kept.
- Left-behind moisture. If you clean your mold with water or alcohol, and it was not fully dry, the moisture left can cause issues, though more commonly this would result in a “tacky” side of the cured product.
While it is unfortunate to end up in a position of flexible epoxy, there is usually nothing you can do about it other than learn from your mistakes. Hopefully, this article has helped you diagnose your mistake (or mistakes) and you will be able to get your work done!
Rest assured that you are far from the first or the last person to make this mistake, and it could even happen again. Keep all the possible scenarios for improper epoxy pouring in mind as you work, it is better safe than sorry, and you will have a well-hardened epoxy resin in return!