I’ve been motivated recently to do some polyester resin casting tutorials. In my opinion, the best place to use polyester casting resin is on a piece where you want to put a high polish on the final casting with a buffing wheel and buffing compound. For this casting, I’m using bangle bracelet mold 414 and a silicone ring mold yet to be released. (You can let me know in the comments if it’s a mold you think you would want to purchase. *wink*wink*) For the inclusions, I’m using dollar store ‘Legos’.
By the way, if you are new to polyester resin casting, I would suggest reading my post on 5 things you need to know before using polyester casting resin before trying this yourself.
What you do not see in this tutorial is me having to talk my peeps that no true Legos were harmed in this making of this bracelet. Trust me when I say it was harder than the casting.
When working with polyester resin, you have to begin with the end in mind. For my castings, I needed to measure the depth of the molds to determine the amount of hardener I needed to use. The plastic mold measures 5/8 inches deep, while the silicone mold measures 3/4 inches deep. According to the manufacturer’s instructions, I need to add 5 to 6 drops of catalyst per ounce of resin.
What you don’t see here is that I am casting this resin outside. Casting the polyester resin in my studio was not an option this week, and because I hate the smell, it had to go outside. Currently, the temperature outside in Florida is in the mid 90’s with fairly high humidity. The ideal temperature for casting this resin is in the low 70’s. I knew I did not need that much hardener, but was dying to know what would happen.
I would regret that decision sooner rather than later.
Because I knew I would not have much time to work once I mixed the resin, I wanted to be certain the block pieces would fit into my mold. This also means making sure they stay below the edge of the mold in addition to being able to fit into the curve of the mold. Once I was satisfied pieces would fit, I prepped both molds with a light mist of Petrolease non silicone mold release.
For this casting, I measured 2 1/2 ounces of polyester casting resin. I knew two ounces should take care of the bracelet, which would leave me an additional 1/2 ounce for the ring. Knowing that I would have to work fast, I didn’t want to worry that I had mixed too little resin. I added 12 drops of catalyst and mixed for approximately two minutes.
Regardless of the resin you use, you will want to pour a little bit into the bottom of your mold before adding inclusions. This will make trapping bubbles in your pieces less likely.
Before adding the toy pieces to the mold, I mixed them in my cup of resin. This breaks the surface tension on the pieces to reduce the amount of bubbles.
I used a stir stix to place toy pieces into the mold. What you can’t see here is that my resin started to gel in under four minutes. While the right amount of hardener was added to the resin based upon my measurements, the outdoor temperature put the resin into overdrive. (The manufacturer instructions state I should have 15 to 20 minutes to work with the resin before it starts to gel.) It was a mad dash to shove pieces into both molds. By the end, I was scooping jelly from my cup.
See? PURE JELLY.
And for those of you wondering how I cleaned up the cup and stir stix? I didn’t. I threw it all away.
I covered the pieces and let them cure. (Still outside. The smell persists for awhile.)
This is my demolded bracelet. (Up side was the pour side, i.e. exposed to air during curing.) Overall, I’m surprised with how it turned out. Putting gelled resin in the mold to fill it up had me concerned about demarcation lines. Luckily, that didn’t happen.
Of course that doesn’t mean there aren’t some other problems I feel compelled to point out to you. (like this is police interrogation or something similar)
A few of my pieces rose up beyond the edge of the mold. I knew this as I was putting the resin in, but didn’t try taking them out once I realized everything was gelling so fast. I would introduce too many bubbles taking pieces out at this point and decided to leave them alone.
I know. I know. You are thinking, ‘Well didn’t you put pieces in the mold before you started this?’ How did this happen? I didn’t anticipate how much the pieces would float in the resin.
I also need to finish the sharp edges on this casting. That isn’t necessarily unusual as resin will rise up along the edge of the mold while curing. Unfortunately, though, I cannot sand the bracelet like I usually do because toy pieces are sticking out of the resin.
I will sand the edges so they aren’t sharp, but the top of the casting won’t be flat. No big deal as the bracelet will be wearable and it is for me anyways.
The only other thing to mention is that the bracelet casting side (side exposed to air) was slightly tacky, but not as tacky as I was expecting. I am hoping it will continue to harden of over the next couple of days. Since I can’t sand off that surface, I will need to use a layer of resin gloss sealer spray to get rid of the tackiness.
So how did the ring turn out?
In case you didn’t believe me about the resin getting hotter sooner than expected, this ring serves as proof. The inside of the silicone mold used for this casting is perfectly smooth, which should have transferred to the ring’s surface. Instead, the resin got hot and created a spider web like cracking to the surface of the resin. The resin is fully cured and the ring is sturdy. Unfortunately though, I don’t think coating with a layer of the gloss sealer spray will get rid of the marks. I could try sanding, but I’m worried I would sand down the toy piece or would need to sand too much off the ring shank to where it would break. If I was serious about trying to salvage this ring, I would recoat it with another layer of resin.
I feel the total need to redeem myself, so let’s call this polyester resin casting Part 1. While I think I can do the bracelet over, and do it better, the ring is still going to be a challenge. Why? The amount of heat needed to cure the shank portion of the ring is different than the top portion of the ring. i.e. If you were casting them as separate parts, you would add different amount of hardener into the resin since they are different thicknesses. It’s going to be hard not to have the cracking again.
What do you think? What has been your experience with polyester resin casting?