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Molding Answered

Anyone know about molding? How do I create the mold, i hear about this oozmoo or something but I cannot find such a thing in the UK. What kind of alternative can i use? how about vaseline around it, would that work? I would experiment but I don't have very much molding stuff.



10 years ago

I would start by having a look at this obscure website called "Instructables", and search through the dozens of tutorials they have available on the topic! ;-)

In particular, Freeman Manufacturing have been posting a whole bunch of very professional videos from their own library over the past couple of weeks.

On a potentially more helpful note...

I think you are referring to Oomoo, which seems to be a specific silicone rubber for mold-making, produced by Smooth-On. There are lots of other materials available as well (clay, plaster,.wax,...)

The stuff that "stops the mold sticking to what ever your molding" is technically called a "mold release agent". You may or may not need one, depending on what material your mold is made of, and what material you're casting into it.

As treb already mentioned, first we have to know what you want to cast, and in what material. Obviously, a mold for jello or chocolate will be vastly different from one used to cast bronze!

I don't have flash installed at the moment for many reasons I'm not getting into. I brought some Polyester Casting Resin to create the mold and I want to mold some RTV silicone (guitar hero fret buttons mod).

Ah - like this Instructable?

Hero Hacks: Key Molding

Most decent size craft or art supplies stores should sell some form of mould making supplies. RTV (Room Temperature Vulcanizing) silicone compound is one of the most commonly used materials. I'd start by looking wherever you bought the polyester casting resin...

The Oomoo 30 used in the i'ble above is room temperature (crucial!), relatively low viscosity (easier to pour/better detail), doesn't need vacuum degassing (handy for the amateur), has a 1:1 mixing ratio by volume (minimal measuring necessary), and a 30 minute pot life (no need to hurry too much, before it stiffens up). You can probably find a different brand that matches this fairly well.

I actually brought some RTV silicone from the same supplier (ebay). From the instructable I thought that oomoo was the mold releasing agent? So what ever mold releasing agent hes using is their a simple alternative, like I've heard someone using that vaseline would that work at all? Mainly asking because my credit card is maxed out :(.

The issue with a silicone mold and this type of polyester resin is not one of mold release, but rather that some of the chemicals in the silicone interfere with the "setting" of the resin (aka "cure inhibition"). So you need something that will form a seal between the silicone and the polyester resin.

Vaseline is often used as a mold release agent, but I don't know how well it would work as a sealant in this case. I *think* it will probably work - worth a try anyway.

I found this other mold making instructable by bofthem, in which he gives a little more info on the sealant he used:

Mold Making: Two Part Silicone Mold


  • Q: What resin did you use? What sealant did you use to prevent it from sticking to the mold?
  • A: I had decent luck using crystal clear spray varnish as a sealant. I would recommend you use mold soap or SuperSeal to coat the mold. Spraying a coat of PVA in the mold before casting will also provide a solid seal. For casting parts out of your mold, silicone usually doesn't need any release or sealant, but the particular resin I was using met some cure inhibition against the RTV. You can find a non polyester clear casting resin and it will probably cast fine without needing any release or sealant.

If you don't happen to have any crystal clear spray varnish, you could try vaseline or even hair spray. If you've never done any casting before, it might be worth doing a small test run to see what works best - good exercise anyway, and you probably have far more mold and casting material than you need anyway.

Brilliant thanks so much for your help :D.

oozoo I take it stops the mold sticking to what ever your molding. So is their a alternative which I can get in the UK or even the garage.

dunno mate, visit hobbycraft i guess and ask those guys they got all sorts in their.

The first thing we need to know...

What are your molding?


What material do you want to cast using your mold?

Here's my instructable on using concentrated gelatin/jello as a mold material... With chapstick as a release agent :) I cast chocolate in there - I also casted a silicone replica of that apple using Dragon Skin (a Platinum class silicone). It worked quite well - it just needed extra cure time as the mold was cool when the silicone was poured...