Urethane

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Lordmagoo

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Ok so recently i got video from smooth-on about making a rubber mold and slush casting. The only difference is that its not silicone... so i was wondering can I use urethane to mold my clay sculpture. Its made of van aken, soft, oil based, plastina clay.

thx
 
Ole'Irish-man said:
Ok so recently i got video from smooth-on about making a rubber mold and slush casting. The only difference is that its not silicone... so i was wondering can I use urethane to mold my clay sculpture. Its made of van aken, soft, oil based, plastina clay.
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Theoretically, you can but it's not ideal for what you're thinking of doing. Urethane is a lot stiffer than silicone so a 1-piece glove molding technique that you saw in Adam's ODST video is not going to work, hence more suitable for multi-part molding technique. Also, if your sculpture has deep undercuts, these will complicate the molding process.

The video below might help. It's by TAP Plastics but the principles are the same.

 
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ok so in the video i got, the model is a sculpture of a face on a pedastal. So thus it had undercuts. they strengthened

the undercuts by thickining the rubber in those areas. The rubber it self had a cut down the back just as in the ODST

film. This is why i ask, the process is almost exactly the same as the ODST video, but with urethane.....
 
no, that's not the reason. You can get urethanes and silicones in different hardnesses. The reason you cant use urethane is because you'd be casting in urethane... and the two would stick. If you were casting in plaster, or concrete... go ahead and use urethane.
 
I just watched the video. I see what you were saying. The urethane they used looks a lot softer than what I'm accustomed of seeing. Well, using urethane is definitely a plus since it's cheaper than silicone, if only slightly stiffer. As long as you stay at 40 or below (Brush-On 40 or Brush-On 35), it should be okay in terms of softness and flexibility. On the downside, you're going to need quite a bit of mold release.
 
the way i see it you will pay just as much money going to buy all the release and dye and stiffener, etc. to do it that way. so im still trying to decide
 
You can cast urethane into urethane, you just need a good release agent to act as a barrier between the products, remember back to chemistry class "like attracts like"
 
NZ-TK said:
You can cast urethane into urethane, you just need a good release agent to act as a barrier between the products, remember back to chemistry class "like attracts like"
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I know you CAN do it. But I don't want to explain all the waxing, shellacking buffing, waxing more etc part of things.


Just use silicone - take our word for it, it's easier (though 50% more expensive)
 
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Ole'Irish-man said:
Ok so recently i got video from smooth-on about making a rubber mold and slush casting. The only difference is that its not silicone... so i was wondering can I use urethane to mold my clay sculpture. Its made of van aken, soft, oil based, plastina clay.

thx
Click to expand...

The trouble with casting a rigid material into a rigid mold (whether it be urethane or plaster or any other material) is the issue of undercuts. An undercut is any area in a mold or sculpture that a cast material can be poured into but cannot be removed. You theorectically could mold your clay with a rigid material, then scrape the clay out of the mold, but when you cast your first resin into the rigid mold, it will get locked into the mold and you won't be able to remove the casting..

Best to use a flexible mold material like silicone, or polyurethane rubber
 
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I know you CAN do it. But I don't want to explain all the waxing, shellacking buffing, waxing more etc part of things.


Just use silicone - take our word for it, it's easier (though 50% more expensive)
Click to expand...

That is absolutely correct, although some of my favourite helmet makers do it all the time, you just have to make sure you don't use any filler in the urethane, it says you can but apparently it never works and things always stick. I agree though, it's easier to use silicone. The price difference between silicone and urethane moulding products is negligible anyway
 
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