Curing Epoxy Resin | Why Your Resin is NOT Curing

I have been seeing a lot of questions from artists in my community groups asking why their resin projects are not curing. I thought it was time to put my thoughts together to help answer those questions.

Please share this article with other resin artists. My goal is to help bring an understanding of epoxy resin to artists. Resin is a fun craft but education is needed prior to jumping in. Resin is a chemical and it needs to be respected to continue to enjoy its use.

Curing Epoxy Resin – SAFETY FIRST!

Creating with resin is fun, but learning how to use it safely is crucial. Believe it or not, safety is one of the most commonly overlooked steps when working with resin. I know I wanted to jump right in and start creating, but I quickly learned that I needed to read up on the safety measures so that I could enjoy this medium for years to come. Here are a few basic safety guidelines to review before you start working with resin:

• Well ventilated area. Working in a room with good circulation and/or open windows is crucial. Some resins emit fumes that can be toxic.
• Gloves. Yes, there is a thing called resin allergy. Wearing gloves is the easiest method to help with ongoing and prevent future skin conditions while working with resin.
• Respirator. Protecting your lungs is a top priority. Wearing a respirator provides consistent protection to your lungs while working with resin. 
• Clean spills immediately. Don’t let resin sit on your table or floor. Use paper towels to scoop up as much as possible, then use denatured alcohol or isopropyl alcohol to clean up any remaining residue.
• Safety goggles. Goggles help prevent unexpected splashes from touching your eyes, but they prevent you from touching your eyes. If you are like me, you will touch your eye without thinking. Getting resin in your eyes is dangerous. If you get resin in your eyes, flush with water repeatedly and seek medical attention immediately!
• Apron. Aprons help prevent resin from getting on your clothes and then absorbing and touching the stomach. When working, you can easily focus on your process and not even realize resin has touched your belly for 5 minutes or more!

Here are a few of my favorite epoxy resin brands that I LOVE to use!

How do you cure epoxy resin?

Curing epoxy resin involves following specific steps and conditions to initiate and complete the chemical reaction that transforms the resin from a liquid to a solid state. You should ALWAYS follow the instructions provided on the bottle of the resin. The curing process typically involves the following steps:

Mixing

Start by carefully measuring and mixing the epoxy resin and its corresponding hardener or catalyst according to the manufacturer’s recommended ratio. Thoroughly combine the components to ensure a homogenous mixture. Follow the recommended mixing time and technique to avoid introducing air bubbles into the resin.

Consider using silicone tools to mix the epoxy resin. Silicone tools are reusable, easy to clean, and will save you money.

Degassing A.K.A Air Bubbles (optional)

If air bubbles are present in the mixed resin, you can use techniques such as vacuum degassing using a Vacuum Chamber Kit or using a torch or heat tool to remove them. Also, pouring the resin slowly, stirring the resin slowly while mixing, and paying attention to how you handle the resin can greatly help you minimize air bubbles in the cured resin.

Consider using silicone tools to mix your resin. Use wood stir sticks can potentially add air to your resin because wood is porous and can hold air.

Preparing the substrate

Prepare the surface or substrate where the epoxy resin will be applied. Ensure it is clean, dry, and free from any contaminants that could interfere with adhesion. Consider sealing any wood surface you are pouring on. Wood can hold onto air which can seep into resin as it cures.

Application

Pour or apply the mixed epoxy resin onto the prepared surface or into the desired mold. Use a brush, roller, or other suitable tools to spread the resin evenly and achieve the desired coverage.

Curing conditions

The curing conditions will depend on the specific epoxy resin being used. Common curing factors include temperature, humidity, and time. Refer to the manufacturer’s instructions or the epoxy resin’s technical data sheet for the recommended curing conditions.

Curing time

Allow the epoxy resin to cure undisturbed for the recommended curing time. This duration can vary depending on the resin formulation and curing conditions. During this time, the resin undergoes a chemical reaction and gradually transforms from a liquid to a solid state.

Post-curing (optional)

Some epoxy resins may benefit from post-curing, which involves subjecting the cured resin to additional heat or UV exposure to enhance its properties, such as increasing its hardness or chemical resistance. Follow the manufacturer’s recommendations for post-curing, if applicable.

It’s crucial to note that the curing process and specific instructions may vary based on the type and brand of epoxy resin being used. Always refer to the manufacturer’s guidelines and technical documentation for the specific epoxy resin you are working with to ensure proper curing and achieve the desired performance characteristics.

Why is my epoxy resin not curing?

If your epoxy resin is not curing as expected, several factors could be contributing to the issue. Here are some possible reasons why epoxy resin may not be curing properly:

1. Incorrect mixing ratio: Epoxy resin requires precise mixing of resin and hardener components in the correct ratio. If the ratio is incorrect, such as using too much or too little hardener, it can hinder the curing process and prevent proper hardening.
2. Incomplete mixing: Thoroughly mixing the resin and hardener is crucial for proper curing. Inadequate mixing can result in areas with unmixed components, causing those areas to remain sticky or soft even after the curing time has passed.
3. Low curing temperature: Epoxy resin curing can be temperature-sensitive. If the curing temperature is too low, the curing process will be slower or may not occur at all. Ensure that the curing temperature is within the recommended range specified by the manufacturer.
4. Humidity or moisture exposure: Epoxy resin can be sensitive to moisture. If the resin or the curing environment is exposed to excessive humidity or moisture, it can interfere with the curing process and lead to improper curing or surface defects. Ensure that the environment is dry and free from moisture during the curing process.
5. Insufficient curing time: Epoxy resin requires sufficient time to complete the curing process. If the resin has not been allowed to cure for the recommended duration, it may remain soft, tacky, or uncured.
6. Inadequate surface preparation: Proper surface preparation is essential for good adhesion and curing of epoxy resin. If the substrate is not properly cleaned, degreased, or roughened, it can hinder the resin’s ability to bond and cure effectively.
7. Old or expired resin: Epoxy resin has a limited shelf life, and using old or expired resin can lead to curing issues. Check the expiration date of the resin and ensure it is within the recommended timeframe.

If your epoxy resin is not curing, review the instructions provided by the manufacturer to ensure you are following the recommended procedures, including the mixing ratio, curing temperature, and curing time. If the issue persists, consider contacting the manufacturer for further guidance or troubleshooting assistance.

Here are a few of my favorite epoxy resin brands that I LOVE to use!

What are some common problems with epoxy resin as it cures?

While epoxy resin is a versatile and widely used material, it can experience certain issues during the curing process. Some common problems that may arise while curing epoxy resin include:

1. Air bubbles: One of the most common issues is the formation of air bubbles within the resin. These bubbles can be trapped during the mixing or pouring process, resulting in unsightly voids or blemishes in the cured resin.
2. Yellowing or discoloration: Epoxy resin can sometimes undergo yellowing or discoloration over time, especially when exposed to UV light. This can affect the clarity and appearance of the cured resin, particularly if it is intended to be transparent or have a specific color.
3. Insufficient curing: Inadequate curing can occur when the resin is not mixed thoroughly, the curing temperature is too low, or the curing time is insufficient. This can result in a resin that remains sticky, soft, or tacky even after the intended curing period.
4. Overheating or exothermic reaction: Certain epoxy resins generate heat as they cure. If the curing process generates too much heat or is conducted in an environment with high temperatures, it can lead to overheating or an exothermic reaction. This can cause the resin to bubble, warp, crack, or exhibit other forms of distortion.
5. Cracking or shrinkage: Epoxy resin can experience cracking or shrinkage if the curing process occurs too quickly or if there is a significant temperature differential during curing. Rapid temperature changes or improper curing conditions can result in stress within the resin, leading to cracks or dimensional changes.
6. Excessive moisture sensitivity: Epoxy resin can be sensitive to moisture, especially during the curing process. If the resin is exposed to excessive moisture or a humid environment, it can result in surface defects, cloudiness, or reduced mechanical properties.

To mitigate these problems, it is crucial to follow proper handling and curing procedures, including thorough mixing, appropriate curing temperatures and times, and proper surface preparation. Additionally, using high-quality resins, following manufacturer guidelines, and understanding the specific characteristics of the epoxy resin being used can help minimize potential curing issues.

Why does my resin flash cure when I put it into a mold?

When Epoxy Resin “Flash Cures”, it means the resin is curing faster than expected. This might seem like a good thing but in most cases with crafters, it is not. The epoxy resin creates a chemical reaction to heat up and cure. When this is accelerated, the resin can become too hot for the mold causing damage, creating excessive toxic fumes, and can cause damage to a crafters project.

Flash curing can happen for several different reasons. If your resin is flashing curing when you put it into a mold, it could be due to several factors:

1. Exothermic reaction: Some types of resin, such as certain epoxy resins, generate heat as they undergo the curing process. When you pour the resin into a mold, the confined space can trap the heat generated, causing the resin to cure faster than usual. This rapid curing is known as flash curing.
2. Catalyst concentration: Resins typically require a catalyst or hardener to initiate the curing process. If the catalyst concentration is higher than recommended or not properly mixed, it can accelerate the curing reaction, leading to flash curing when the resin is placed in a mold. Always refer to the mixing instructions provided on the bottles for the specific resin you are using!
3. Mold temperature: The temperature of the mold can affect the curing process. If the mold is warm or heated, it can accelerate the resin’s curing reaction and cause flash curing.
4. Thin mold walls: If your mold has thin walls or is made of materials that conduct heat well, it can lead to faster heat transfer from the resin to the mold. This increased heat transfer can expedite the curing process and result in flash curing.
5. Excessive heat or light exposure: If the resin is exposed to excessive heat or intense light during or immediately after pouring it into the mold, it can trigger a rapid curing reaction, leading to flash curing.
6. Pouring too deep: Always check with the specific brand of resin you are using to see their recommendations. In general, the resin can be safely poured about 1/8″-1/4″ thick, while Deep Pour Resins can pour about 1-1/2″-4″ thick.

It’s important to note that flash curing may also lead to potential issues like an increased exothermic reaction, reduced working time, or compromised resin properties. It’s recommended to follow the manufacturer’s guidelines to achieve the desired results with your resin casting process.

Here are a few of my favorite epoxy resin brands that I LOVE to use!

How does humidity affect the curing of epoxy resin?

Checking the humidity of your workspace might seem a little odd when working with resin but it is actually very important. Humidity refers to the amount of water vapor present in the air. It is a measure of the moisture content in the atmosphere.

To put it simply, resin and water do not mix. If the humidity of your workspace is high, chances are good that your resin project will not cure properly.

1. Pot Life: The pot life refers to the working time available for mixing and applying epoxy resin before it begins to harden. Higher humidity levels can accelerate the pot life of epoxy resin, meaning it will start curing more quickly. This is because moisture in the air can initiate the chemical reaction that causes the resin to harden.
2. Cure Time: The overall curing time of epoxy resin can be affected by humidity. Higher humidity levels can slow down the curing process, causing the resin to take longer to fully harden. Conversely, low humidity levels can accelerate the cure time. This is because humidity affects the rate at which moisture is absorbed by the resin, which is necessary for the curing reaction to occur.
3. Air Bubbles: Increased humidity can lead to the formation of air bubbles in the epoxy resin. When there is excess moisture in the air, it can become trapped in the resin, resulting in the formation of bubbles. These bubbles can negatively impact the appearance and structural integrity of the cured epoxy.
4. Surface Finish: High humidity levels can affect the surface finish of epoxy resin. Moisture in the air can cause the resin to cure more slowly, resulting in a longer open time. During this extended open time, dust and other particles in the air may settle on the resin’s surface, leading to a rough or textured finish.

To minimize the impact of humidity with curing epoxy resin, it is important to work in a controlled environment with appropriate temperature and humidity conditions. Additionally, using a dehumidifier or air conditioning can help regulate the humidity levels in the workspace. Following the manufacturer’s instructions for the specific epoxy resin product you are using is crucial to ensure proper curing, as different resins may have varying sensitivities to humidity.

What is a good humidity level when working with epoxy resin?

When working with epoxy resin, maintaining an appropriate humidity level is crucial to ensure proper curing and the best possible results. The ideal humidity level for working with epoxy resin typically falls within a specific range.

In general, a relative humidity (RH) of around 40% to 60% is considered suitable for working with epoxy resin. This range helps to strike a balance between allowing the resin to cure properly and minimizing potential issues related to excessive moisture in the air.

If the humidity is too high, above 60%, it can cause the epoxy resin to cure more slowly and potentially result in a cloudy or tacky surface. Excess moisture can also lead to bubbles forming within the resin, affecting its clarity and finish. High humidity can also prolong the curing time and increase the risk of surface imperfections.

On the other hand, if the humidity is too low, below 40%, the epoxy resin may cure too quickly, resulting in a shortened working time and potentially trapping air bubbles or causing uneven curing. Low humidity can also lead to excessive evaporation of volatile components in the epoxy resin, resulting in a higher risk of shrinkage and cracking.

To maintain the desired humidity level when working with epoxy resin, it may be necessary to use dehumidifiers or humidifiers, depending on the ambient conditions. It is also important to ensure good ventilation in the workspace to minimize the accumulation of moisture.

It’s worth noting that specific epoxy resin products may have their own recommended humidity ranges. Therefore, it’s essential to consult the manufacturer’s instructions and guidelines for the particular epoxy resin you are working with to achieve the best outcomes.

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