What’s the Difference Between Epoxy and Resin?

If you’ve just been getting into woodworking or serious DIY projects, then you have probably heard about how awesome epoxy can be. You may also find yourself getting confused when people use the terms “epoxy” and “resin” because they don’t always seem to be the same thing. So, is there a difference?

Technically, there is no difference because epoxy is a resin. However, there are three different resins commonly deployed in DIY projects: epoxy resin, casting resin, and polyester resin, each with unique properties. Also important to note, epoxy resin and epoxy glue are different products.

If this still seems a bit confusing for you, fortunately, we have created a guide to help you work through each type of resin (and to examine the glue confusion too) so that you can pick the right product for your next epoxy project. First, we will look at the three main types of resin (including epoxy resin). Then, we will look at the differences between these types.

What Types of Resin Are There?

Before we take a closer look at the detailed differences between the epoxy (resin) and (casting) resin, it is important to look at what types of resins there are in the first place.

Interestingly, there are actually three types of “resin” used in projects. They are epoxy resin, casting resin, and polyester resin. You need to choose the right type of resin for the right use, or things can go very wrong.

In general, there are two types of resin that are in common use in home DIY projects – epoxy resin and casting resin. Then, polyester resin is also used, but this is particularly used for the marine industry and not commonly used for epoxy DIY projects.

So, what are the three types of resins?

1. Casting Resin. Casting resin is thinner and runnier (that means it has a lower level of viscosity) than epoxy resin and that can be either a help or a hindrance when you are working on a specific project.

2. Epoxy Resin. Epoxy resin, on the other hand, has a faster cure time than a casting resin will have. This can be an advantage, but it also means that you have a shorter time period to work with epoxy before the curing has progressed too far to move the materials around.

In turn, the viscosity and cure times lead to a need for a thinner pour depth with epoxy than with casting resin. Finally, epoxy resin tends to come with very simple mix ratios (typically 1:1) whereas working with casting resin can be rather more complicated than that.

3. Polyester Resin. Polyester resin is less important in relation to DIY projects (like epoxy and woodworking combinations) because it is mainly used in the marine industry. Polyester resin tends to be used for quick fixes rather than long-term use because it is much more brittle and prone to cracking – however, it’s completely UV resistant (unlike epoxy resin) and cheaper to use than epoxy. It is also water permeable (e.g. water can pass through a polyester resin bond).

Now, let’s take a look at the detailed differences between epoxy resin and casting resin to better answer your original question.

Typical Uses of Epoxy (Resin) and (Casting) Resin

Epoxy resin is mainly used in woodworking. It’s great for creating coatings that are durable and weather resistant and for filling in wood when rot or other structural weaknesses have taken place. It may also be used for bonding two surfaces together.

Casting resin, on the other hand, tends to be used more in crafting situations such as working on molds, figurines, and jewelry.

It’s worth noting that despite these traditional applications – it is often possible to substitute one type of resin for another (depending on the application, of course) without any kind of catastrophe taking place in your projects.

Thickness Of The Liquid (Viscosity)

Epoxy resin is typically a much thicker liquid than its casting resin counterpart. This isn’t arbitrary – it’s because when you use an epoxy resin, it takes less time to cure and the reaction is much more exothermic (that is – it releases heat) than the casting resin reaction.

For a casting resin, this means that you can pour a casting resin to a thicker depth than an epoxy resin without damaging the bonding within the resin. However, if you wanted to use a casting resin to provide a coating – it’s much harder to do than with epoxy resin because the low levels of viscosity make it easy for the casting resin to run off the sides of your project.

So, if you do decide to use casting resin to coat something; you will probably want to build a frame or another kind of mold to keep it on the surface while it cures.

Different Cure Times

The “cure time” of a resin is the period of time it takes for the resin to form the final product. In general, though there are exceptions, epoxy resins take about 12-24 hours to cure. Whereas the casting resins normally need about twice as long to cure (24-48 hours).

This isn’t the whole story, though. Epoxy resins “gel” (that is they start to resemble the finished product and can no longer be easily adjusted) within 20 minutes of the two-halves being mixed. This means you will need to work quickly with epoxy to get the job done.

In contrast, the casting resins can take up to 18 hours to gel! That means you have plenty of time to work with a casting resin without worrying about needing to make adjustments later.

The more severe exothermic nature of epoxy resin leads to a second set of challenges too: First, they can produce too much heat after being mixed (you may only be able to keep a large amount of epoxy in a mixing container for 5 minutes). Second, if you apply the epoxy in too deep of a layer, that heat can cause the curing epoxy to crack and it will damage both the appearance and strength of the bond.

Working Time or Gel Time

We touched on this a moment ago, the gel time (sometimes also called the “working time” or “pot time”) is important to consider.

Working with epoxy resin means that you’re going to have about 20 minutes (plus or minus 5 minutes) to get the epoxy mixed and poured (or otherwise used) before it’s too stiff to work with.

If you go past the gel time, it can also be hard to get bubbles out of the epoxy layer. More annoyingly, the gel time can be reduced if you’re working in a hot place or if you’ve mixed large quantities of the two halves of the epoxy resin together.

This means that when you work with epoxy, you want to keep your eye on the time while you work or you risk having to start again.

In contrast, casting resin gives you ample time to work considering how long it takes to gel (up to 18 hours). Consequently, your working time will be prolonged, and you will have plenty of time (compared to epoxy resin) to make adjustments or final touches.

Pour Depth Limits

Epoxy resin can normally be poured to a depth of about ¼” – 1/8”. If you pour epoxy any deeper than this – you are going to find that it is going to be too exothermic a reaction, and your epoxy will crack.

You can add additional layers of epoxy over already cured epoxy, of course, but this may add substantial amounts of working time to the project.

Casting resins, on the other hand, are so much less exothermic that you can often pour them to depths of many inches. This is why casting resin is so popular for making molds or other projects where you are looking to achieve a very deep layer of encapsulation.

The Finished Product – Hardness

In most cases, you are going to find that epoxy resins come to a finished product that is harder than that produced by a casting resin.

However, it’s worth noting that you can mix casting resins in a variety of ways and that means they can vary considerably in hardness from project to project.

This can be a very useful property. If you want to build in a degree of flexibility to the end product – then you can mix your casting resin so that it is less hard but more capable of expanding or contracting (for example).

To achieve this change in the property of the casting agent, you will normally reduce the amount of curing agent (the hardener that you use) in the mix.

However, a fully cured epoxy resin will always be more scratch-resistant (no matter the level of hardness attained by the casting resin) than the casting resin.

The Finished Product – Clarity

Epoxy resins are never quite as clear as casting resin. Though this doesn’t usually matter when using epoxy for coating other materials, it is still important to note the aesthetic that this type of resin will provide you with.

Contrarily, one thing that’s nice about working with casting resins is that they cure to a clean glass-like finish. That means If you’re looking for that perfect transparent and translucent look – you’re going to want to go with a casting resin.

Standard Mix Ratios

*The ratios given here are given as “resin:curing agent”.

Epoxy resin is usually mixed in a 1:1 ratio. That does not mean that there are no variances in this, and you should read the packaging on your epoxy resin before you mix it to ensure that 1:1 applies in your circumstances.

However, as we have already seen – casting resins can be mixed in different ways to achieve different results. A 1:1 ratio will result in a hard end product without much flexibility, a 3:1 ratio, on the other hand, is going to give you a very flexible resin which is quite soft.

It’s important to read the instructions carefully when using casting resins and measure the two components carefully.

UV Resistance

Epoxy resin and casting resins in their natural state are not UV resistant. Both of them when left exposed to UV for long periods of time will become yellower and may even become weaker.

This is always going to be more noticeable when the resin is used in a standalone application because then there’s no other color to interfere with the color of the resin. That means casting resins are more prone to appearing discolored than epoxy resins (which are usually used to coat something else).

However, if this is likely to be an issue for your project – you can buy epoxy resin and casting resin which have had UV inhibitors added to them. This is going to help them resist the discoloration process when kept in natural light.

Bubbling In Your Epoxy/Resin

If you have spent much time using resin, then you will know that both epoxy resin and casting resin can end up cloudy and discolored due to bubbles forming in the resin itself.

If you find that the product is full of bubbles on the shelf, then it is best to deal with these bubbles prior to mixing the two parts of the resin. You can see our in-depth guide to handling bubbles in epoxy resin, here.

When working with epoxy resin pay special attention to corners, grooves, etc. which can easily trap bubbles.

However, casting resins tend to have less noticeable bubbles and they can usually be drawn to the surface easily and popped even after you’ve poured the resin.

We have found that you get fewer bubbles (in any kind of resin) if you have properly sealed the surface you want to work on with a very thin coat prior to working.

Heat Tolerance

The resins that most people buy for home use are not generally designed to withstand very high temperatures. You are going to find that both casting resin and epoxy resin will soften (even after curing) at temperatures of 150 degrees Fahrenheit.

This is something that you want to take into account when building a kitchen work surface, for example, that you intend to put hot pans, mugs, etc. on.

The good news is that you can buy epoxy resin and casting resin that is designed to withstand much higher levels of heat. But, the bad news is, of course, that these are quite a bit more expensive than the standard resins – so you want to make sure you really need them before you invest in these products.

Exceptions To The Rules

None of the “rules” that we’ve given above are hard and fast or set in stone. The problem is that the resin market is fairly complex and there are dozens of clever products out there designed to help you get around the limitations of a material.

Unique product purchases. In general, if you want something out of the ordinary from a given resin – you are probably going to have to pay a bit more for it. You can check with your local hardware store to see if they carry a product which does what you want and to get a price for it.

Scratch-resistance. We’d also note that you can use a casting resin to create a coating on wood, for example- it’s just a bit more work because you will probably have to build a frame to work in. You should also be sure that scratch-resistance is not very important because casting resins scratch way more easily than epoxy resins do.
Multiple stages. You could also use an epoxy resin to carry out a casting job. You will probably need to do this in multiple stages though given that you have a limited pour depth when working with epoxy.

We find that it can pay to be creative. If you have a bunch of epoxy in your shed and you want to carry out a project – it might be better to work out how to use that up rather than rush out to buy some casting resin, instead. We are big believers in being friendly to your wallet and to the environment.

Conclusion

What’s the difference between epoxy and resin? Well, not much if the truth be told. Because epoxy is a resin. However, as you’ve seen – there are 3 types of resin commonly used in projects and it’s important to select the right resin for the right job. In particular, you need to know the difference between casting resin and epoxy resin for home projects.

As for the difference between epoxy glue and epoxy resin? It’s mainly down to the packaging that the glue is sold in – it’s made out of epoxy resin.