Friday, April 6, 2012

Resin Casting: 1 Part Molds

I apologize for the brief hiatus. School has been keeping me really busy, but I have been squeezing in hobby time here and there. My latest projects have me working on casting as I have chosen Necrons as my second amy, but I don't want to pay a ton of money for canoptek scarabs.

Ron over at From The Warp did a great tutorial on making scarabs from epoxy ribbon (aka Green Stuff) and I messed around with that, but the cure time takes way too long and I wanted something faster. Eventually I will get into 2 part molds and specifically how to make scarabs, but I want to start on something simpler so I can explain the process. Today I have a tutorial on 1 part molds made from Instant Mold and plastic resin. Here is what you need to get started:
  • Instant Mold (Bought mine from TheWarStore)
  • Smooth-Cast 300 (Bought mine from Smooth-On)
  • Blu-Tack. This is the stuff used to hang posters on the wall. Make sure you buy get actual Blu-Tack. There are a few other brands out there including a white version and one by Elmers. In my experience, they don't work well at all. Get the good stuff.
  • Legos. My kids have tons of these, but you can order whatever pieces you need right from the Lego website.
  • A piece with a flat side to cast. I casted one of the skulls from Games Workshop's Arcane Ruins, but you can do a chapter icon, a Rhino door, or something similar. Just make sure one side is perfectly flat.
  • X-Acto Knife
  • 3 small mixing cups.
  • Sand paper.
Step 1: Build a mold box. I use Legos for this step as they work the best. You want to build a box that is just slightly larger than your part. You also want to build a second piece you can press down on top of your mold. Here is what mine looks like.

Step 2: You need to attach the piece you will be molding to the bottom of your mold box with Blu-Tack like I did below. Make sure the piece sits firmly down and doesn't have any raised edges or the Instant Mold will get under the piece and mess up your mold. I took my walls off to make sure my part was secure.

Step 3: Put the Instant Mold in hot water. I actually boil my water on the stove and cut the Instant Mold down into little pieces. This stuff dries super fast and once it starts to dry, the Instant Mold won't stick to itself so make sure its really hot.

Step 4: Shake off any excess moisture and quickly push the instant mold over the main detail of the part. Fill in all of the gaps and use your press to push down on the mold. Like I mentioned previously, this stuff dries really fast. If you mess it up, don't worry. Instant Mold is reusable and you can heat it up and try again. When you push down on your part, your press piece may stick. This is fine and don't mess with it. Put the mold in the freezer for about 15 minutes and come back to it.

Step 5: You are ready to de-mold your part. Take your mold box apart and remove the molded piece. Carefully pry out your piece with your finger nail or with an x-acto knife.

Step 6: You'll see there is a bit of flashing on the mold from pressing too hard. Just trim the mold with your knife and save the pieces. You can use them later. I heat mine up and roll the unused Instant Mold into a ball. Our mold is done and now we are ready to make our first cast!

Step 7: Working with resin can me messy. It needs to be mixed in equal amounts. I use a cup for each part because pouring from the bottle is way too messy. Nothing will stick to Instant Mold, so you don't need to use mold release or anything like that. Once you have equal amounts of part A and part B, pour them into your mixing cup and mix it well for a minute or two. Make sure to scrape the sides of your container.

Carefully pour the resin into your molds and start the pour on the lowest point of the model. This helps alleviate air bubbles. Don't over fill your molds. You can slightly go over, but you don't want resin pouring out all over as you'll have to sand the pieces flat later on which can be a pain. You'll see I did overfill one of the molds below, but that's the 2 part mold for the scarabs and we'll discuss how that works next time.

Step 8: This is the most agonizing step: waiting till it's done. As the resin cures, it'll get white in the middle and eventually expand out to the edges. This whole process should take about 15 minutes or so and when it starts, it'll happen pretty quickly. You don't want to de-mold the part too soon and ruin it, so be patient!

Step 9: Now that the resin is dry you can remove the part from the mold. You can use either your finger or a hobby knife. Below you can see the molded part and the original. Success! 

Step 10: Take your hobby knife and clean up the flash from around your part. You'll also want to run the back across a piece of sand paper to smooth everything out. If you look closely, you can see some minor imperfections here and there. I'm no master mold maker, but if you ask me this looks a hell of a lot better than Fine Cast.

Below are some of the other pieces I've casted along with the scarabs I have been doing. This method is fairly quick and I can pop out about 3 casts in an hour.

Next time, we'll talk a little bit more about casting and we'll tackle the process I used to create a 2 part mold for the scarabs. Have a Happy Easter!

Until then,
–The Harrower


  1. Very nice and much quicker than the greenstuff route it appears. Thanks for posting a good step by step too.

    Ron, FTW

  2. Very nice tutorial. I especially like the idea of using a press.

    It should be noted that not all resins are supposed to be 1:1 ratios. After filling the mold, have you tried scraping excess resin off with a flat tool (the back of a butter knife, paint mixer, etc.)

  3. Ron: Thanks. Without your tutorial, I would have never got the inspiration to work on this.

    Meigeall: Regarding the ratios, I was specially referring to Smooth-Cast 300, but I can see where that could lead to confusion. I'll update the post. Also, never thought of just scraping off the excess. Funny how the simplest things escape us sometimes.

  4. Just in case anyone didn't notice, Dedard now has major sponsorship from Coca-cola. Notice the product drop in the pics? :P

    Awesome tutorial. I definitely have a few items I'm considering doing this for.

  5. This article has inspired me to make molds, it's a very simple step by step and without reading this, making molds would still be a magical mystery to me. So, thankyou very much.

    Any chance we'll be seeing your two part mold for the scarabs any time soon? :D

    Oh and BTW: nice job on the ETL. ;)

  6. Big question here...
    I was under the impression that resin hardened thru chemical heat, which, wouldn't that melt the instant mold (I have both and have been avoiding using them together).

  7. Resin does harden through heat, but it doesn't get nearly hot enough to affect the Instant Mold. You have to heat water to boiling temperatures when working with Instant Mold, so you are good to go. It might be an issue with larger molds or a different resin, but with the set up I described it works fine. I've done dozens of casts and experienced no issues with the molds.

    1. I have instant mold and some resin, so I will have to try it out, I was just worried cuz it seemed the resin got a lot hotter than the water I used to soften the instant mold.

    2. It could be the type of resin you are using. Your mileage may vary, but with Smooth Cast-300 it works great.

    3. I have some of the smooth cast 300 on order, look forward to trying it with the instant mold.

      Did you ever try 2 part molds with it yet tho?

    4. I've done 2 part molds of Necron Scarabs and it works fine. I haven't tried anything bigger yet though.

  8. you can also use fiberglass resin from wallmart 14 dollars and some change for alot of the stuff. just make sure to release the mold with Pam.

    1. Interesting. Doesn't fiberglass have fibers in it though? Can you use it on molds this small? I would love to see some pics...

  9. Did you ever get to the 2 part mold? Great article btw gonnna pick up some of that instant mold

    1. I've done Necron Scarabs as a 2 part mold. It wasn't as good as creating a proper silicon mold, but it worked.

    2. Ahh k been trying to make a multiple scarab mold with silicon with no luck