Friday, October 23, 2020

Epoxy Resin - Casting Resin vs Coating Resin

Have you ever poured epoxy resin onto a canvas only to have it all run off so that you are left with only a very thin coating? 

Or have you poured your epoxy into a mould and found that it was full of bubbles that just wouldn't rise to the top?

Then chances are, you were using an epoxy resin that wasn't designed for the project that you were making. Not only is there more than one type of resin, but there are several types of epoxy resin and they are all designed for different types of resin work!
Transparent turquoise resin being poured around wood slices in a square silicone mould. Text overlay reads Coating Resin vs Casting Resin - What are the differences?

To keep it simple, let's look at two general categories of epoxy resin and why artists and crafters need to know the difference.

When shopping for epoxy resin, you need to look closely at the packaging. 

Box of EpoxyCast resin and box of EnviroTex Lite resin with finger pointing out the type of resin on each box.

You might notice that some epoxies are labelled EPOXY CASTING RESIN and some are called EPOXY COATING RESIN. Some other names for coating resin are:

  • bar or tabletop resin
  • pour-on resin
  • artwork resin
  • doming resin.
So what's the difference between a casting resin and a coating resin? They're both epoxies, RIGHT? 

Well, they each have different characteristics that make them suitable for two totally different types of resin work.

Let's take a closer look at them.

Epoxy Casting Resin. 

Casting resins usually have a lower viscosity, i.e. they have a thinner consistency which makes them ideal for pouring into moulds. 

Because of their thinner formulation, casting resins can pick up even the finest detail in a mould. 

Their low viscosity also means that any bubbles stirred into the resin during mixing can easily rise to the top of the mould where they can be popped. 

Epoxy casting resins generally take longer to reach soft cure, the stage where you can handle the resin without damaging it. And because it produces less heat during curing, you're able to do deeper pours than with coating resins, without the risk of the resin overheating, cracking or yellowing as it cures.

All these characteristics make epoxy casting resin the right resin for pouring into moulds to make items like jewellery, small homewares and memorabilia. The long working time allows you to embed objects such as flowers, insects or other ephemera to preserve the item forever. 

Epoxy Coating Resin

On the other hand, epoxy coating resin is more viscous. It's designed for pouring onto level surfaces like table tops, resin artwork and for doming. Because of its thicker consistency, it will stay on the surface without running over the edge too quickly, leaving you with a thick, lustrous, high-gloss coating. 

When you mix coating resins, it's normal to mix a lot of bubbles into the resin due to how thick coating resin is. These bubbles can be easily popped once you've poured the resin onto the substrate because the coating will only be about 3mm (1/8") thick.

In general, coating epoxies are harder than casting epoxies because they need to take more knocks (but there are always exceptions!). You also have less working time with coating epoxies and they reach soft cure stage much faster.
Insulated steel tumbler coated with marbled purple, white, pale mauve and gold resin

Some coating resins are classified as safe for indirect food contact so they can be used for coating tumblers, wooden cheeseboards and countertops that will come into contact with food. 

Choose a FOOD-SAFE resin for tumblers and charcuterie boards.

Detailed view of green, glack and gold geode-inspired resin art

Coating resins which don't have the incidental food contact rating, are perfect for coating artwork to give it a lustrous high-gloss finish, or for creating resin paintings such as geode-inspired resin art. 

Here's a quick comparison of the different characteristics casting and coating epoxy resins have:

Chart with bullet points highlighting the charactistics of casting epoxy and coating epoxy

Can You Interchange the 2 Types of Epoxy Resin?

Now that you know the most significant characteristics of these two epoxies, it's easier to understand why you need to choose one that was designed for the resin project you have in mind. If you want to pour it into a mould, use a casting epoxy. If you want to create a piece of resin art, choose a coating epoxy.

But what if you want to pour epoxy into a mould and all you have on hand is a coating epoxy? 

Or if you have a casting epoxy but you want to create a piece of resin art? 

Will it work?

The short answer is: Yes, it will still cure. But you will run into some issues... and you may not get the result you were hoping for.

If you pour a thick coating resin into a mould, it will be filled with bubbles that will remain suspended in the resin, unable to rise to the top of the mould because the resin is so thick. 

And if you use casting resin to coat a surface, you'll end up with only a thin layer of resin instead of a thick coating because a lot of it will flow over the edge of the painting or tabletop as it tries to find level.
Dirty resin pour in shades of yellow and green with white cells done with casting resin and flowing straight off the canvas

There are always ways of overcoming these problems but the better solution is always to use the RIGHT TYPE of epoxy resin for your project.

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Learn why you should choose the right type of EPOXY for your resin project

Happy Resining!

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