Urethane vs. Silicone

[Akademee]

I have become interested in making small molded props for both me and possibly to sell to members of the 405th. I went to Smooth-on and did my research on what molding compound I should use and which ones I could afford. The two obvious choices came down to Urethane rubber vs. Silicone rubber.

I found that the urethane came off a bit cheaper for the material purchased than silicone. I couldn't see any disadvantage to it other than it mentioned something about a shorter 'Library Life." How much of a decrease in mold stability over time are we talking about here and is there a way to preserve urethane rubber molds longer?

I plan to make 2-part molds for small parts, not big skin molds for helmets and such.

Thanks 405th!

 

[torsoboy]

The urethane rubber does have a shorter shelf life. It also deteriorates the more you use the mold, faster than silicone rubber. Urethanes tend to be a more advanced-user material too, so if this is your first venture into mold making, it may prove difficult to work with. In addition to this, even though they are "flexible", bending the mold off the product over and over (even just a few times) allows for the molecules to stretch and break, causing tiny tears pretty early in relation to silicone rubbers (silicones are specifically designed for a longer life over repeated flexing). I started on Urethane rubbers, and once I went to silicone, I was hitting myself for not trying it first.

Another thing to consider is that Smooth-On silicone rubbers tend to not require mold release for most casting products. It'll just pop right out. With urethanes, you need to get a mold release agent. I know that fiberglass resin will bond to urethane rubber without any release agent. I know from personal experience - had to destroy my best mold at the time because I forgot to use a mold release. Plus, one thing about mold releases is that a lot of companies that sell online report it as a hazardous material to their shipping companies. So even if you found a cheap spray can of it, sometimes you'll get slammed by hazardous material shipping. So that throw's the whole "cheaper option" out the window.

Just go with the easier choice - Smooth-On silicone rubber. No need to make it any more complicated, and certainly no need to cause yourself any headaches from forgetting the mold release.

 

[Akademee]

Thanks, you just saved me a lot of headaches!

 

[bebb]

Hi everyone, I've been using Pepakura for a while now and I'm just getting into using clay for modelling. I'm just wondering what material would be best to make the mold and and to pour inside it.

I've been watching this tutorial http://www.youtube.com/user/gametavern#p/u/32/fH3OsGqltL4 and he used a liquid plastic to pour into the mold. Does anyone know what liquid plastic he used or is there a better alternative.

Any help will be really useful.

 

[PSYCHO ARMY]

I believe he uses smooth cast 300 but I was told by another member that smooth cast 320 is the better alternative due to its longer pot life, time it has less air bubbles.