Friday, March 30, 2018

Friday Fun - Starting Resin Casting

After a bit of a hiatus - and given that the resin casting stuff has been scattered, untouched, on my worktable for far too long - I decided to jump start my layout progress by jumping into resin casting.

I've mentioned before that I've had this cool Micro-Mark resin casting starter set for over 3 years. Unfortunately, when I tried at first to use it, I'd discovered that the molding rubber had gone bad. Well, not to be (too) deterred, while I waited for a new shipment of rubber molding materials, I decided to test the resin casting materials by giving the molding clay a try. 

The clay included with the starter set comes in a block, so the first step was to spread & flatten it out so it could cover/accommodate the wall I wanted to cast as a test.

The instructions recommend using talc as a mold-release agent. I didn't have any talc and, frankly, didn't know where to get any. I figured "talcum powder" would be close, but nobody had any of that either. Thankfully, The Missus suggested looking at the ingredients for some "talcum powder like" products. I eventually discovered - wait for it - baby powder (can you tell we don't have kids?) - which is made up primarily of talc and fragrance.

So I sprinkled some on the test piece I was using as a master, brushing it into all the nooks and crannies, and tried not to think of diapers . . .

Next step was a bit harrowing - I needed to press the master into the clay as firmly as possible while keeping everything even (not pressing too hard on one side/end or the other). This turned out to be more difficult than anticipated since the master was pretty flexible.

As you can see, my effort came out okay but not quite as great as I'd hoped. No worries though - this is just a test.

Next, I measured out equal amounts of the two parts of resin into two separate cups, then poured them into a third, larger, cup and mixed them together, trying hard to keep bubbles from forming. Once that was done, I slowly poured the resin into the clay mold (I'd already made certain that the mold was level in all directions).

I thought I'd get clever and keep the back of the casting nice and flat by weighing it down, placing a piece of Saran Wrap (aka cling film) between the resin and the weight to allow for easy separation.

I think next time I'll use a piece of plate glass. As you can see above, the Saran Wrap wasn't exactly all nice and flat as I'd hoped. The back of the casting is all crazy wavy. Oh well.

Thankfully though, the front looks just fine. It has a little distortion caused by my not pressing the master into the mold as evenly as I should have (another use for the plate glass and weight, I reckon), but overall it's passable - especially for a background flat.

And here's a comparison of the original/master and the casting. I haven't bothered yet to remove all the flash (and getting those windows cleaned up properly will be a challenge), but I think it looks pretty good for my first time.

Here's a couple of quick tips/lessons if you decide to use the clay for your mold:
  • Use it only for a relatively small part/master that you intend on copying/casting once. The clay - and thus the mold - will distort has you remove the casting. Consequently, additional castings will likely be distorted and may not even be usable.
  • If you want to keep the back of the casting flat and use Saran Wrap/clingfilm to keep the resin from sticking to anything, be sure that it's pulled & taped perfectly taut so that you don't get the waviness I experienced. If I try this in the future, I may just use a piece of flat plate glass with mold release sprayed on it.
Since my Rt. 15 bridge parts/masters will need to be duplicated a number of times, I'll be using the rubber mold material instead of the molding clay. But that requires that I make a mold box, with my master inside. On the advice of Don Janes (when he was here what seems like forever ago now), I decided to use an old part for a master as a test.

The master is itself a casting of junkyard parts (courtesy PeteL) which I hot glued on to a piece of foamcore. I made the rest of the box by hot gluing more foamcore together.

And that's where things are until the rubber meets the road arrives from Micro-Mark.

Like with so many things in this hobby, the dread of the unknown all too often prevents us from even trying a new technique or skill. I may have had beginner's luck, but I'm pretty happy with how this whole resin casting thing has gone so far. It's not rocket science - and the Micro-Mark starter set gives you everything you need to get, um, started.

But it's the Dave Frary video that comes with the set that's really worth its weight in gold. He takes you step-by-step through the process and, if you follow his instructions, you'll get good results. At least I have so far. We'll see how the rest of this journey goes . . .


  1. It is better to use a piece of overhead acetate or similar between the resin and plate glass backing, as occasionally urethane resin will stick to glass - don't ask me how I know,


  2. Hi Chris. Enjoying your posts about casting. When using plate glass I have put a very light coating of Pam cooking spray on the side that will lay on the resin. I have found the cured casting will lift off easily from the glass leaving a nice flat back on the casting. Just spray it on the glass then smear it around with a Kleenex to cover the surface. It doesn’t seem to affect the surface of the rain in any way.