At Carved, we use epoxy resin to create our wooden iPhone cases. However, we get tons of questions about casting resin, too, so we wanted to explain the difference between epoxy resin and casting resin and why we prefer one over the other.
That’s not to say that casting resin doesn’t have its place in the art and woodworking world; it’s just not the right choice for our projects. But if you’re planning to use resin for a larger, more robust project, casting resin may be the perfect choice for you. Let’s explore the differences between the two.
What are the main differences between epoxy resin and casting resin?
Let’s clarify a few things first…Resin is a viscous, liquid polymer that, when combined with a hardener, undergoes a chemical reaction to become a solid, glass-like material. It’s one of the more complex mediums to work with, and our choice of resin at Carved.
The most common resin type is epoxy resin, a popular choice for artists to create resin artwork like jewelry, table tops, flower molds, and sculptures.
Just as there are other types of resin, epoxy resin has several sub-categories, each with unique characteristics and use cases. Some of these include casting resin, coating resin, clear epoxy resin, and UV-cured epoxy resin. To learn more, check out our guide on the types of epoxy resin.
One of these types of epoxy resin is casting resin, which has a low viscosity, meaning it’s more like water than honey. Casting resin is best used for projects that require a thick, heavy pour, such as filling deep grooves on a live-edge wood table or covering a large object in resin.
Epoxy resin, because of its lower viscosity, is more widely used by artists because it’s ‘thinner.’ It combines well with resin and hardener to create a clear, hardening liquid plastic. It’s typically more adhesive than casting resin, making it more compatible with wood, metal, and fiberglass, forging a solid and durable bond.
An excellent analogy between the two is printer paper vs. construction paper, where epoxy resin is like printer paper and casting resin is a thicker, heavy-duty construction paper. Yes, they’re paper-like and similar, but they have slightly different characteristics based on your needs. Similarly, casting resin is more like water, whereas epoxy resin is more like honey or maple syrup.
Those are the basics; let’s get into the specifics:
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Curing time – Casting resins generally take longer to dry (up to 72 hours) and cure completely (up to 7 days), providing a more complex, rigid finish. Epoxy resins, contrastingly, dry faster (12-24 hours) and cure entirely within 48-72 hours, presenting varying levels of flexibility based on the specific formulation used. If you plan to use casting resin, factor in the extra time needed to cure.
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Heat resistance – Epoxy resin is far more heat-resistant, making it the optimal choice for surfaces exposed to high temperatures, such as kitchen countertops and bar tops.
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Viscosity—Casting resins are generally lower in viscosity (fast and runny) than epoxy resins, which are higher in viscosity (slow and sluggish). The low viscosity of casting resin enables it to be poured in thicker layers without trapping bubbles. Check with the resin manufacturer to see how thick of a layer you can safely pour. The higher viscosity of epoxy resin lends itself to easier resin coloring.
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Working time—Working time is the period after mixing resin when it’s physically workable before thickening. It is affected by the temperature and volume of the resin, with warmer conditions and larger volumes shortening it. Between the two, casting resin generally has a longer working period than epoxy resin because of its lower viscosity.
- Use cases—Casting resin is used in many industries, from making jewelry, embedding objects, and creating deep, clear-layered art pieces to industrial manufacturing. Its lower viscosity makes it perfect for filling gaps or cavities without trapping bubbles, producing facades or cladding, or making detailed replicas of sculptures. On the contrary, epoxy resin is generally easier to paint on and commonly used for coatings and adhesives, where clarity isn’t as important.
Epoxy resin is the go-to for clarity in resin projects, especially for thin pours. At Carved, we use it to make our wooden phone cases, pocket knives, wallets, and monoliths—it’s our favorite!
Casting resins are used more for their hardening properties, which make them perfect for casting molds. Both types find their way into jewelry making, but the use depends on the desired result—epoxy for thinner, shinier finishes and casting for thicker, more rigid pieces.
Lastly, pour depth is one of the most important factors when deciding between casting resin & epoxy resin. Casting resin is best for thicker pours than those typically achieved with tabletop epoxy resins. Compared to epoxy resin, casting resin allows a much thicker pour at once without trapping bubbles and reducing the time required for completion.
Performance and Durability Differences
Once you get the hang of it, resin art is pretty straightforward. However, before you begin creating your masterpiece, there are a few important things to consider regarding your resin choice.
Hardness and Flexibility
The hardness of cured resin varies greatly between casting and epoxy resins. Casting resins have a higher Shore hardness (a measure of the resistance a material has to indentation), making them more rigid and less flexible. Their hardness and low viscosity make them ideal for intricate projects, such as jewelry making and mold casting with resin. Epoxy resins can exhibit varying levels of flexibility, contingent upon the specific formulation used. This flexibility means it can be used in various projects, from tabletops to phone cases. Once cured, epoxy resin projects can last for years if maintained properly.
Air Bubbles and Clarity
Epoxy resin is an exceptionally high-quality and UV-stable variant, and it minimizes yellowing over time and offers outstanding clarity. By applying thin layers and using a heat gun or torch, you can remove any trapped bubbles and improve the transparency of your epoxy resin project. Casting resin is clearer and glossier even when subjected to hardening. This results in finished pieces with fewer air bubbles and a striking clear finish.
UV and Heat Resistance
Tabletop epoxy resin is quite heat resistant, thus reducing risks such as yellowing, smoking, and cracking that can occur if the epoxy is accidentally overheated. Its UV resistance prevents discoloration and maintains the vibrancy of embedded objects for extended periods, which is why our phone cases retain their color for years.
Comparatively, casting resin is less resistant to UV lighting exposure and may become yellow over time. While it is important to note that all types of resin should not be exposed to excessive heat or direct sunlight, epoxy resin, by its nature, is more heat—and UV-resistant.
How to Choose the Right Resin for Your Project
With so many factors to consider as you prepare to handcraft your artwork, there’s no overarching right or wrong answer to the question, “Which resin should I use for my art project?”
The truth is, it depends – it depends on a few things…
Are you coating surfaces or filling molds?
Epoxy resin is self-leveling in nature and is predominantly utilized for coating surfaces. It's favored for casting thin layers, usually no more than 1/4 inch thick, over smooth, flat surfaces such as tables, bars, counters, and artworks. Thicker layers increase the risk of overheating, smoking, yellowing, cracking, or even making your epoxy fisheye (dips, separations, or irregularities in a flat epoxy coating).
On the other hand, casting resin is the best option for filling molds and creating detailed objects. Due to its low viscosity and lengthier cure times, casting resin enables intricate details to shine through jewelry making, mold replicating, and object embedding.
How much resin do you need?
When it comes to resin projects, size does matter. Incorrect calculations could result in resin wastage or shortage.
In addition to the other elements we’ve covered, cost may be a factor for your project. You don’t want to purchase too much or too little, forcing you to buy more or let some go to waste. Similarly, thin-pour coating epoxies poured thicker than recommended could result in accelerated reactions, leading to cracks, yellowing, or fisheye.
To calculate how much resin you’ll need for a specific project, calculate the volume of the pour area (L x W x H), then divide that number by 1.805 to convert the cubic inch volume to U.S. fluid ounces.
Frequently Asked Questions
Can you mix casting and epoxy resins?
No, mixing casting and epoxy resins is not recommended. They have different curing times and properties, which can lead to inconsistent and potentially flawed results. Use each type of resin for its intended purpose to ensure optimal performance.
How long can you store casting and epoxy resins?
Casting and epoxy resins can typically be stored for 1-2 years if kept in a cool, dry place and sealed correctly. Always store outside direct sunlight and check the manufacturer's guidelines for specific storage recommendations.
Why not use epoxy resin?
Epoxy resin may not be suitable for specific applications due to its sensitivity to UV light, which can cause yellowing over time, and its limited heat resistance compared to other resins like polyester or polyurethane. Choose the resin type based on your project's specific requirements.
Does casting resin break quickly?
Casting resin is generally durable, but like glass, it can break if subjected to heavy impact or stress. Proper curing and handling are essential to maximize its strength and longevity.
Is epoxy resin the same as resin?
Epoxy resin is a resin type, but not all resins are epoxy. Various resins, such as polyester and polyurethane, have different properties and uses.
Can you use epoxy resin for casting?
Yes, epoxy resin can be used for casting, but it's best suited for smaller projects or shallow pours due to its slower curing time and tendency to overheat in thicker layers. For larger castings, use a resin specifically designed for deep pours.