What is the Recommended Time to Leave Epoxy Resin in the Mould?

What is the Recommended Time to Leave Epoxy Resin in the Mould?

Jan 19, 2024

Epoxy resin is a versatile and popular material used for various projects, from crafting to industrial applications. One common question that arises when working with it is how long it should be left in the mould. Its curing time can vary depending on several factors. One of the primary reasons for leaving it in the mould is to preserve the shape and form of the final product. 

As the resin cures, it undergoes a chemical reaction that transforms it from a liquid to a solid state. In this blog, we will explore the factors that influence the curing time and provide guidelines on how long you should leave the resin in the mould for optimal results. To get a better understanding of this, we recommend enrolling in a resin art course


Recommended Curing Time of Epoxy Resin

While curing time can vary, here are some general guidelines to help you determine the appropriate duration for your epoxy resin project:

  • Initial Cure: In the beginning, the cure typically occurs within the first 24 to 48 hours. During this time, the resin will reach a solid state, but it may still be slightly soft.
  • Full Cure: Achieving a complete cure can take several days to a week, depending on the resin formulation and thickness. It is advisable to allow at least 3 to 7 days for the resin to fully harden before subjecting it to any stress or load.

[Pro Tip: Testing the Cure: To ensure that your epoxy resin is fully cured, you can perform a simple test. Gently press your finger against a small, inconspicuous area of the resin surface. If there is no dent or fingerprint left behind, it indicates that it has cured completely. However, if an indentation is visible, the resin may require additional time.]

Tips for Achieving Proper Cure of Epoxy Resin

To achieve a successful epoxy resin cure, here are some additional tips to keep in mind:

1. Use the Right Temperature and Humidity

The epoxy resin cures best within specific temperature and humidity ranges. Avoid curing in extremely hot or cold environments, as it can negatively impact the curing process. Maintaining a temperature between 70°F and 85°F (21°C - 29°C) with low humidity is ideal for most epoxy resins. Consider using a temperature-controlled environment or a curing box to achieve consistent results.

2. Follow the Manufacturer's Instructions

Each epoxy resin brand may have its own set of rules for curing. It is important to carefully read and follow the manufacturer's recommendations to ensure the best results. Pay close attention to the mixing ratios, handling times, and curing durations specified by the manufacturer.

3. Properly Prepare the Mould

Before pouring epoxy resin into the mould, make sure it is clean, dry, and free from any debris or contaminants. Dust, dirt, or moisture can compromise the curing process and result in imperfections. Use a mould release agent or apply a thin layer of silicone spray to facilitate easy release after curing.

4. Mix Thoroughly and Accurately

Properly blending epoxy resin and its hardener is crucial for a successful cure. Follow the recommended mixing ratios precisely to ensure a thorough chemical reaction. Use a separate container for measuring both components and stir them together slowly, making sure to scrape the sides and bottom of the container to incorporate all the resin and hardener effectively.

5. Avoid Overmixing and Trapped Air

While it's important to combine epoxy resin thoroughly, excessive mixing can introduce air bubbles, affecting the final result. Avoid vigorous stirring or using high-speed mixers, as this can trap air in the mixture. Instead, stir gently and consistently for the recommended duration to minimise the risk of bubbles forming.

6. Eliminate Air Bubbles

To remove any air bubbles that may have formed during mixing, use a heat gun or a handheld torch to pass over the epoxy surface gently. Be careful not to hold the heat source too close or for too long to prevent overheating or scorching the resin. The heat will help the bubbles rise and pop, leaving you with a bubble-free surface.

7. Allow Sufficient Curing Time

Epoxy resin requires adequate time to cure fully. Rushing the process can result in an incomplete cure and lead to soft or tacky surfaces. Refer to the manufacturer's recommendations for the required curing time, and be patient during the process. It's crucial to allow enough time for the resin to harden and achieve its maximum strength.

8. Post-Cure for Enhanced Properties

Some epoxy resins benefit from a post-cure process that involves applying additional heat or leaving the cured project in a warm environment for an extended period. This post-curing step can improve the resin's mechanical and chemical properties, providing a more robust and durable finished product.

Factors Affecting Curing Time of Epoxy Resin

Several factors can influence the curing time of epoxy resin. Here are the key factors to consider:

The Temperature

One of the most significant factors that can impact the curing time of epoxy resin is the temperature. Epoxy resin cures faster in warmer temperatures and slower in colder temperatures. The optimal temperature range for curing epoxy resin is typically between 70 and 80 degrees Fahrenheit. If the temperature falls below this range, the curing process will be delayed, whereas higher temperatures can accelerate the curing process.

Mixing Ratio

This is another important aspect that can affect the curing time. When epoxy resin is mixed with a hardener, it undergoes an exothermic reaction, which generates heat and initiates the curing process. It is crucial to follow the manufacturer's instructions and maintain the correct mixing ratio of resin to hardener. Deviating from the recommended ratio can result in incomplete curing or extended curing time.

Humidity Levels

These can also have an impact on the curing time of epoxy resin. High humidity can slow down the curing process, while low humidity can speed it up. It is advisable to work in a controlled environment with optimal humidity levels to ensure consistent and predictable curing times.

Thickness of the Resin Layer

The viscosity of the epoxy resin layer in the mould can affect the curing time as well. Thicker layers tend to take longer to cure compared to thinner layers. This is because heat generated during the curing process takes longer to dissipate in thicker layers. It is important to consider the desired curing time when determining the thickness of the resin layer to achieve the desired results.

Air Flow

Proper air circulation around the epoxy resin in the mould can significantly impact the curing time. Sufficient airflow helps in the removal of residual heat generated during the curing process and allows for faster curing. It is recommended to use fans or ensure proper ventilation in the curing space to maintain an ideal airflow.

Epoxide Equivalent Weight

The epoxide equivalent weight is a measure of the molecular weight of the epoxy resin. It plays a crucial role in determining the curing time. Epoxy resins with lower epoxide equivalent weights tend to cure faster compared to those with higher weights. Consideration should be given to the epoxide equivalent weight of the epoxy resin being used, depending on the desired curing time.


Various factors, including resin type, hardener ratio, temperature, and humidity, influence the curing time for epoxy resin in the mould. While a minimum curing time of 24 hours is recommended, leaving the epoxy resin in the mould for at least 48 hours ensures optimal strength and durability. 

It is important to follow the manufacturer's instructions and maintain the recommended temperature and humidity levels for consistent results. By adhering to these guidelines, you can achieve a successful epoxy resin cure and maximise the performance of your projects. To learn more about resin art, visit Arts Shala's website or Contact Us for further questions.

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