Epoxy Vs Resin: Does It Really Matter?

The short answer, for this very complicated question, is “Yes!” You can choose polyester resin, casting resin, and epoxy coating, among others. Each has a different job, requires different cure times and different ratios. A bad mix may crack, yellow, or fisheye. In order to have a great outcome for your project, you need to understand the differences. Then choose the best for your project.  

Types of Epoxy

One thing that most people fail to realize is that the compounds that make-up polyester resin, casting resin, and epoxy coatings are very different. Polyester resin is used mostly in marine applications. Polyester Resin works well for refinishing a boat deck or the interior of the cabin. This is not something that most “crafters” want to use. 

Therefore, we will focus on Casting and Coating resins.

Coating Vs. Casting: Their Respective Purpose

These two epoxies are worlds apart if you look specifically at their intended use.  

Coating Resin is used when you want to protect a piece of furniture or make it prettier by putting a layer of “liquid glass” over it. It is ideal for bottle cap tabletops or putting photographs on a wooden wall plaque. 

Casting Resin is meant for applications like jewelry making, casting figurines, and molds. 

Each one can potentially do the job of the other, but you have to change the application process. To cast using coating resin, you need to pour several thin layers instead of filling the mold completely on the first pour. If you want to coat using casting resin, you may need to build a dam around your project surface to ensure it doesn’t run off of the wood.

Major Differences/Similarities of Epoxy

 We will look at each separately because each of these differences may determine which one is going to be more effective for your projects.

Viscosity/Thickness

Casting resin is typically thinner. It produces less heat and takes a longer time to cure. It can be poured into molds or other projects that have a dam to avoid a runoff. 

Thicker coating resin does run, but it still stays in place well enough to coat the substrate, builds up a higher amount of heat, and cures faster.  

Cure Times

Typically it will take between 36-48 hours for a casting resin to fully cure. However, casting resins often gel in about 18-hours. 

Coating resin takes around 12-24 hours to cure. Gelling begins in about 20 minutes. 

The difference comes with their “heat” (exotherm). When working with coating epoxy, if it sits in the mixing container for 5-10 minutes, you will notice a lot of heat and a huge increase in its thickness.

Working Times

As previously stated, with coating epoxy you have a lot of heat buildup within ten minutes. This is an indication that it is starting to set. If you continue to watch it, you will see that within approximately 20 minutes, the resin will become harder to work with. It is harder to remove bubbles or move the epoxy around.

Casting epoxy has a longer gel or “pot” time. Therefore, can work it longer. 

Mix Ratios

When considering mix ratios, casting resins vary more frequently. Casting resins can have a 1:1 ratio, 2:1 ratio, or 3:1 ratio, but there are other possible variations depending on a person’s needs. Generally, 1:1 ratios are preferable because it is the easiest to work with. When using varied ratios you need a graduated mixing container to ensure even more accuracy. 

Coating epoxy often have a 1:1 ratio (IE-1-cup to 1-cup or 1-gal to 1-gal). It should be measured exactly.

Pour Depth

Coating epoxies generally require only 1/8-1/4-inch pours per application. If you go too thick cracking can occur due to an accelerated reaction. 

Contrarily, casting resins can be poured several inches thick per application. This is why most people choose a casting resin for their molds, encapsulation projects, and river tables.  

Bubble Susceptibility

When working with epoxy of any kind, you risk bubble formation on the substrate or encapsulated items. Casting resin’s thinner compound may allow bubbles to rise to the surface and pop easier. However, the steps you take to prepare your project, the fewer bubbles you will see.

When using porous (wooden) material, you can lessen the risk of bubbling by applying a very thin layer of epoxy to seal it. Tiny pores, grooves, corners, or other open areas will hold air. When you pour (as in encapsulating) air trapping areas must be minimized. Seal coats reduce the risk of air being trapped to the surface of encapsulated items. 

Hardness

Generally speaking, coating resins will be more scratch-resistant. Casting resin often allow for varied mix ratios, which can alter the cured product harder or softer. Sometimes, softer is preferable. When creating “fake water” in a glass vase, soft is best. The epoxy must allow for expansion and contraction at a similar rate to glass.

UV Resistance

Casting and coating epoxy often contain inhibitors that help to minimize yellowing due to UV rays. UV rays/exposure  can cause yellowing in cured epoxy. It can be noticeable on thicker, stand-alone casting projects. Other noticeable variables depend on the color of the wood, paint, or stain. Lighter colors will make yellowing more obvious. This is why most casting and coating epoxies have warnings that say NOT recommended for use on outdoor furniture or anything that may be placed permanently in direct sunlight. 

Heat Tolerance

Both casting and coating resins are designed for the average DIY type of person. They do not handle extreme heat well and may begin to soften in environments where heat exceeds 120-150°. If you are planning to coat countertops that may come into direct heat with hot pots or pans, utilize hot pads, coasters, etc. 

Differences In Resins

 Each type of resin serves different purposes. The key is to understanding the intended application of both coating epoxies and casting resin. In summary, casting resins are for thicker applications and coating (table top and bar top) epoxies are for coating applications.