1. The smell is horrible.
I admit my nose is sensitive to smells, but I have read the same comments from other resin casters as well. For me, I will NEVER use this resin inside my house or office. I will use it inside an enclosed space (like a garage) if I can leave the space, close the doors, and leave for twelve hours or more. When working with this resin, I use a NIOSH approved respirator for fumes.
*Note: these are not required according to the safety information of the polyester resins I use, but I find the smell bothers me that much.
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 to me, the smell is that bad.
If you want to get a respirator, this article details the one I use: resin safety precautions
2. This resin is not for beginners.
It requires more skill in several respects. First, the pot time is shorter than many epoxies, generally 8 minutes or less. Note: The polyester resins I have used state their pot time is not that short. Maybe it is because I’m in a warm-weather climate, but none of the polyester casting resins I have used have ever gone more than 10 minutes before starting to gel.
To make things even harder, 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 are struggling to get a good mix with larger volumes of hardener mixed into the resin, you are not going to be successful only mixing in a drop or two of hardener into the resin.
For beginners, I recommend starting with epoxy resin. They are easier to work with and can also get you great resin casting results.
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 is not 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 is needed. This is because thin layers are unlikely to generate enough heat to cure so it needs extra hardener.
Why is this important? You can’t mix the resin thinking you can pour it in any 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.
4. The shelf life on polyester casting resin is no more than 6 months.
While many epoxies will work for years if properly stored (although the hardener may start to yellow), six months is generally the longest you can expect polyester casting resin to stay in usable condition. Note: In troubleshooting users who purchased their polyester casting resin from a ‘big box store’, oftentimes, I find the resin was likely purchased after the 6-month shelf life. I make sure Resin Obsession rotates stock regularly to give customers the longest shelf life possible for all of our products.
5. The surface exposed to air during curing will remain sticky, even after the resin has cured.
So with all these disadvantages to using polyester casting resin, why should you consider 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. That means you do not 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, shiny finish. That being said, however, if a polyester casting is dropped on a hard surface, it is likely to break.
Polyester resin is also generally ‘moisture insensitive’. Your environment’s humidity generally does not affect its performance.
What has been your experience with polyester casting resin?
Polyester casting resin is not something I recommend for beginners. Before you give it a try, get good with epoxy resin first. To help you with that, I wrote the instantly readable book, Resin Fundamentals. It takes you from confused to confident with resin in only an afternoon!
Unpublished Blog Posts of Resin Obsession, LLC © 2020 Resin Obsession, LLC