Wake up this morning thinking about using polyester casting resin?
Who wakes up in the morning thinking that? (Even I’m not waking up in the morning thinking that.)
Then why does it matter?
The problem is that if you go to some of those big box crafting stores (which you shouldn’t — more on that in a minute), you can buy this stuff.
Except crafters don’t understand what they’re buying.
Like resin is resin, right?
No. Never. All resins aren’t epoxy. (But epoxy is resin.)
Polyester is a resin, but it’s not close to epoxy. It’s kinda like your second cousin, once removed, who stands at the end of the third row for family reunion pictures.
If you’ve accidentally bought polyester casting resin (most people) or you want to give it a try (not most people), here’s what you need to know first:
1. The smell is horrible.
I will NEVER use this resin inside my house or office. Instead, I use it inside an enclosed space, like a garage. Then, I leave the garage, close the doors, and don’t reenter for twelve hours or more. I always use a NIOSH-approved respirator for fumes when working with polyester casting resin.
If I didn’t have a NIOSH-approved respirator, I would only use this resin outside. I would also have a fan blowing fresh air on me or evacuating air away from the casting. Yes, I realize this is overkill, but at least for me, the smell is that bad.
⭐️ BONUS: There’s a link to the respirator I use in this article about resin safety precautions
2. This resin is NOT for beginners.
If you’re new to this, don’t use polyester casting resin. It requires more skill.
- The pot time is shorter than many epoxies, generally 10 minutes or less. Epoxy resins have a pot time of 20 minutes or more.
- Polyester casting resin does not mix in a 1:1 or 2:1 formula but instead requires drops of hardener per ounce of resin. If you’re struggling to thoroughly mix epoxy resin, you won’t succeed in mixing polyester casting resin.
If you’re a beginner, start with epoxy resin. They are easier to work with and you’ll get excellent resin casting results.
⭐️ BONUS: Here are some all-in-one resin starter kits that are great for beginners.
3. You have to start with the end in mind.
While you can mix a volume of epoxy and use it as you please, polyester casting resin isn’t that simple. The amount of hardener you add is dependent on the depth of the final casting. It seems counterintuitive, but the thinner the casting, the more hardener you need. Thicker castings need fewer drops of hardener.
In other words, you can’t mix the resin, thinking you can pour it into any resin mold you have. You might end up with a resin casting that doesn’t cure or one where the resin heated up too quickly and cracked.
⭐️ BONUS: Here’s how to figure out how much resin you need.
4. The shelf life of polyester casting resin is no more than 6 months.
While epoxy resin has a shelf life of 1 year or more, six months is the longest you can expect polyester casting resin to be usable. After that, the resin hardens all by itself. You may go to use it one day only to find it’s a solid brick.
This brings me back to the ‘box store’ comment. I’ve helped more than one resin crafter who told me that their resin was hard from the first time they tried to use it. That means the resin was older than 6 months when they bought it.
That comes from not rotating stock.
Something Resin Obsession takes pretty seriously. In fact, Resin Obsession resins are made in small batches so you can get the freshest epoxy possible.
⭐️ BONUS: The 10 questions you need to ask before you buy resin.
5. The surface exposed to air during curing will remain sticky, even after the resin has cured.
You’ll either need to sand down the tacky surface or seal it with a layer of clear acrylic spray to cover the stickiness.
And this surface will stay sticky indefinitely. I’ve got some pieces that are going on ten years. And still sticky.
⭐️ BONUS: Here are other reasons why your resin is sticky.
So with all these disadvantages to using polyester casting resin, why would you ever use it?
Polyester resin castings cure very hard.
They cure hard enough that you can use a buffing wheel and compound to polish polyester resin castings. You don’t have to recoat with another layer of resin or a gloss spray to get a shiny surface. A few seconds on a buffing wheel is all it takes to get a bright, glossy finish.
Polyester resin isn’t affected by humidity.
It cures well, even in the hot and humid summers of Florida.
Confused by all the resin information out there?
I get it. I felt the same way when I started with resin crafts almost 17 years ago. It’s why I wrote the ebook, Resin Fundamentals. It takes you from confused to confident with resin in only an afternoon. Buy the PDF book now and get an email download link in a few minutes.
Unpublished Blog Posts of Resin Obsession, LLC © 2023 Resin Obsession, LLC