Emergency casting

Owen E Oulton · Post by **Owen E Oulton** » Tue Dec 29, 2009 11:53 pm

Well, I needed a few small parts cast and I didn't want to wait a full day for RTV to set up, so I took a tip from the Terragenesis site and tried some plasticene as a mould. The parts were small - two were 1/4" square and one was 3/4" square. Both had some detail, but were less than 1/8" high. I dusted some ordinary school grade plasticene (oil-based modelling "clay") with powder (I'd recommend talcum, but all I had was some baking soda) and carefully pressed it over the detail parts, the lifted it being careful not to distort it, then poured in a small amount of resin (I used EasyFlo 60, which sets up quickly in small amounts. after a few minutes, once it was completely hard, I demoulded. I scrubbed the parts with some liquid soap and an old toothbrush to remove the traces of plasticene and soda, then primed them. Sand the back on some 400 wet-or-dry, and glue them with superglue, and they look like ones from a real mould! I hope this tip is useful for others!

Edit: I wrote this before actually finishing the priming, and they're somewhat coarser than I thought they'd be, but still useable as battle-damaged parts, which is what I wanted anyway. Unfortunately, they're not as good as I implied above, but still useful...

Jagdson · Post by **Jagdson** » Wed Dec 30, 2009 12:41 am

That was a good reminder about dusting the clay. A lot of times it doesn't really feel that sticky, but it can sure act that way.

I've made a few fast & dirty molds like that, but using Sculpey. The advantage over plasticene is that the polymer's not very oily. I've found that using Sculpey as a part to be molded isn't as easy, since it seems to like mold rubber.

Have you tried pouring a mold over plasticene, and if so how did it behave?

Stu Pidasso · Post by **Stu Pidasso** » Wed Dec 30, 2009 12:42 am

Sounds great! Thanks dude!

Owen E Oulton · Post by **Owen E Oulton** » Wed Dec 30, 2009 12:51 am

RTV does and doesn't work over plasticene. Tin-catalysed stuff isn't too bad, but platinum-catalysed stuff usually won't work. The problem is the sulphur in many brands of plasticene. Platinum is used in catalytic convertors on cars to remove the sulphur, so it inhibits the catalysis. It's not so bad with tin-catalysed RTV's like GI-1000, which will even set over Roma Plastilina, a very high quality and high-sulphur clay... Experiment with some leftover RTV from another job first - just pour a few drops of RTV onto a blob of Plasticene and see if it sets up...

Unfortunately, my tip wasn't as good as I thought. Perhaps chilling the Plasticene with the master still in it, and using talcum would work better.

en'til Zog · Post by **en'til Zog** » Thu Dec 31, 2009 2:35 am

I've done the plasticine trick, using gel super glue. Worked well.

Spray in a little accelerator.
Dribble in a little gel.
Spray in a little accelerator.
Dribble in a little gel.
Repeat as needed.

Oh, and LET THE SG SET before trying to demold. Otherwise it's a gel bomb in a thin candy shell.

Chacal · Post by **Chacal** » Thu Dec 31, 2009 6:12 am

Plasticine is, when you look really close, grainy. That'll make your cast parts grainy too. It could be great to replicate cast-iron parts in scale.