Frequently Asked Questions

Cured epoxy resin is inert and should be disposed of as you would other solid non-hazardous waste. Uncured resin, or residue left over in jugs, must be disposed of properly as the hardener and resin are unreacted. If the jugs have been sufficiently drained, they may be recycled but the amount of allowable residue will be determined by your local hazardous waste collection center and the prevailing regulations. When contacting your local waste collection center, you will need the Safety Data Sheets that are available for download from our website.

Heat is released during the chemical reaction that converts liquid part A and part B into solid epoxy. The amount of heat released depends on the epoxy’s chemistry and the amount of epoxy used. That is, a certain amount of mixed part A and part B will result in the release in a certain amount of heat.

The curing epoxy must be able to shed the heat it generates efficiently enough to avoid overheating. The ability to shed heat is largely governed by the ratio of top surface area that is open to the air relative to the volume.

For the same resin system, thinner castings will have greater top surface areas in comparison to overall volume and will shed heat more efficiently. Thicker castings cannot shed heat as efficiently and may overheat.

For the same volume of epoxy, a thinner casting will have a larger top surface area and will shed heat more efficiently compared to a thicker casting with a smaller top surface area.

How volume affects exothermic reactions

EcoPoxy systems are developed to have reactivity levels suited to their intended applications. Always consult your product’s Technical Data Sheet or Application Guide for recommended volume and thickness.

Listed below are a few possible causes of why an epoxy project doesn’t cure:

• Wrong mix ratio – Too much resin or too much hardener will result in unreacted product left that cannot form cross-links. This can result in a project that is tacky or a soft cured epoxy.
• Poor mixing – Poor mixing can result in uncured resin. This can affect the entire project or be localized to small areas that remain tacky. Even with careful mixing, some areas of the mixing cup may have remnants of unmixed resin and hardener. This is why we recommend that you do not scrape the sides or bottom of the container when pouring, to get every drop.
• Temperature is too low – If the ambient conditions or epoxy temperatures are too low, the chemical reaction necessary for curing the liquid epoxy to a solid will be slow to start. Consult the product’s Technical Data Sheet for recommended working temperatures.
• Insufficient resin mass – Most casting resin systems rely on the generation of heat from the reacting resin to complete the curing process. If there is not enough reacting resin generating heat, the cure will proceed extremely slowly.

Individual resin systems are formulated to have an appropriate reactivity level for their end application. However, other factors play a role in how an epoxy cures. These factors are listed below:

• Mix ratio – Follow the mix ratio closely. Keep in mind volume and weight ratios are different. Inaccurate mixing is a common cause of cure-related issues.
  
  
• Inadequate mixing – Mix the product for the recommended duration. Make sure to scrape the sides and bottom of the container during mixing. Ensure product is clear and streak free before use. Do not scrape the container when pouring. Unmixed resin can result in soft or tacky areas of uncured resin on your project.
  
  
• Ambient conditions – Resin will cure faster in warmer conditions and slower in cooler conditions. At the extreme, working in areas that are too warm or too cold can result in overheating or failure to cure, respectively. Follow the recommendations for working temperatures in the product’s Technical Data Sheet.
  
  
• Temperature of your resin and hardener – Similar to ambient temperature, warmer products will react more quickly than colder products.
  
  
• Project size or volume – Larger or higher volume projects will generate more heat and will cure faster. These projects have the potential to overheat and should be monitored during cure. Lower volume projects will be slower to cure.
  
  
• Ability of your project setup to shed heat – Due to the resin system’s chemistry, it will generate a certain amount of heat to complete the cure. These formulations are tailored to cure as fast as possible while avoiding overheating. The ability to shed heat is related to the surface area of the project relative to the volume of resin used. Additionally, the mold or mold material will insulate the curing resin and may play a role in overheating.

This article provides an introduction to working with epoxies and general principles that apply to casting, coating and laminating systems.

Mix Ratio

The most common causes of curing issues are inaccurate measuring and improper mixing. Measure and mix part A and part B carefully and thoroughly. Modifying the mix ratio, such as adding more hardener will not make the epoxy cure faster, but will result in incomplete curing. Consult your product’s Technical Data Sheet for the correct mix ratios by both volume and mass.

If you are new to mixing resins, begin with a small test batch to get comfortable with how the product mixes and cures. This will provide you with an idea of the system’s working time in your ambient conditions. Use small batches until you are comfortable with the processing characteristics and be aware that larger epoxy batches will react more quickly and have shorter working times.

Epoxy Cure Stages

Mixing resin and hardener starts a chemical reaction that transforms the liquid components first to a gel and then finally into a solid.

• In the liquid phase, the epoxy can flow. All work should be completed in this phase, the working time corresponds to epoxy being in its liquid state.
• As chemical bonds (cross-links) form, heat is released, and the epoxy will heat up and thin before rapidly thickening. Once the mixture begins to gel, the epoxy will no longer flow and should not be manipulated.
• The final stage is solidification. At this point, the epoxy is highly cross-linked and will begin to develop mechanical properties and hardness. Once the epoxy has achieved significant hardness and cooled to ambient conditions, it is ready for finishing.

Epoxy cure stages as a function of time and temperature

There are various processing milestones that occur throughout these cure stages:

• Working Time begins when Part A and Part B are first mixed together and continues until the epoxy begins to thicken. Specified working times are based on application immediately after mixing is complete. Working times can be significantly shorter if resin is left in the mixing container for too long. Up until the working time limit is reached, the epoxy can be manipulated to achieve custom effects. It will self level and allow bubbles to rise to the surface.
• Tacky to Touch is the period where an additional application can be done without the need to abrade the surface of the previous layer. During this period, the project will need to be protected from contaminants that can adhere to the surface. To determine tacky to touch, wear gloves and lightly touch the surface of the casting. No resin will stick to the glove’s surface, but tackiness between the glove and surface will be apparent. The onset of tacky to touch has not been reached if the surface significantly deforms in this process.
• Set to Touch is the point in time immediately after the tacky to touch period, where the surface of the project is tack-free. An additional layer is not recommended without first abrading the surface of the previous layer. Determine if set to touch has been reached using the same method as tacky to touch. There is no observable tackiness between the glove and the surface.
• Demolding Time is the point in time at which the casting has cured sufficiently such that it can be carefully removed from the mold without causing damage to the epoxy. Although the project is solid, it is not fully cured and may sag under its own weight. The project should be supported until it reaches a fully cured state.
• Full Cure is the point in time when the project achieves full mechanical properties.

Processing milestones vary between products, consult your product’s Technical Data Sheet for these milestones.

Epoxy Temperature and Curing

Epoxies will take longer to cure at lower temperatures and will react faster with greater exotherm under warmer conditions. Several factors contribute to temperature:

1. The ambient conditions, or temperature of your work area.
2. The temperature of your resin and hardener, or the area where it is stored.
3. The temperature of the surface to which you will apply the epoxy.
4. The heat generated by the resin system during cure, or exothermic heat.
5. Ability of the curing resin and the mold material to shed heat.

Consult the Technical Data Sheet for your EcoPoxy product for recommended storage and working temperatures.

How Volume affects Exothermic Reactions

The conversion of epoxy resin and hardener from a liquid to a solid involves the formation of cross-links that release heat (exotherm). The amount of heat released depends on the amount of epoxy used; a certain amount of mixed part A and part B will result in the release of a certain amount of heat.

However, if the curing epoxy is unable to shed heat efficiently, the result may be overheating. The ability to shed heat is largely governed by the ratio of the top surface area that is open to air relative to the volume. For the same resin system, thinner applications will have greater surface areas in comparison to overall volume and shed heat more efficiently. Thicker applications cannot shed heat as efficiently and may overheat.

How volume affects exothermic reactions

For example, a coating epoxy poured into a cup at several inches of depth can achieve temperatures that can melt a plastic cup. In a traditional coating application, this resin would be applied thinly enough to be able to shed heat to avoid overheating. This is because a coating application has a much larger top surface area relative to volume.

If a cup of mixed epoxy begins to kick off (enters the initial cure phase and heats up uncontrollably), if possible, quickly move it to a well-ventilated area away from flammable materials. If there is time, the cup can be placed in a water bath to help cool it down. Avoid breathing fumes. Do not dispose of the mixture until cooled.

Epoxies are a type of plastic formed from the polymerization (smaller molecules joining together to become longer molecules) of polymers or pre-polymers containing epoxide groups. Plastics (polymers) fall into two categories, either thermoset or thermoplastic. Thermosets cure through a chemical reaction that results in the formation of cross-links.

Figure 1. Unreacted polymer units (left), as they become linked (middle) to fully cross-linked (right)

The formation of cross-links is an irreversible, or permanent reaction. This means that a cured thermoset will not melt when reheated and will remain solid. Technologies are being developed to break down these types of plastics for recycling, or via other biodegradation methods but are not readily accessible. Consequently, cured epoxy resin is not bio-degradable nor recyclable.

When mixed at the stoichiometric ratio, all the reactive groups will be consumed, and the cured resin will form an inert solid.

Consumer vs. Industrial

Resins are formulated with specific characteristics for the intended market of the product. Consumer resins have more aesthetic requirements such as colour, clarity, and ease of use. Development of these formulations may trade off mechanical performance to obtain better colour and clarity that are important for users.

In contrast, industrial resins often have more defined performance specifications such as high strength or stiffness, wear resistance or flame resistance. These formulations could be used as structural adhesives, composite resins or specialty coatings in automotive or aerospace. They are developed to meet performance criteria but may have compromised aesthetics and are less user friendly.

For example, FlowCast is a consumer resin and has been developed for clarity and low viscosity but is not suitable for structural applications. In contrast, GelCoat is a light industrial resin. It has been developed for high performance in composite applications and is a durable protective coating but does not have a simple 2:1 or 1:1 mix ratio.