Two part mold - mold pieces wont come apart

[Hawk312]

So I am making a two piece mold to cast tires. I placed the tire in modeling clay and created the bottom mold. I then I removed the clay and created the top mold. But I guess I didn`t use enough mold release or something, and now the top part and bottom part of the mold are stuck together in spots it appears. Is there a way to break these parts apart nicely without cutting? I was debating using the freezer method that breaks apart glued styrene, but thought I would see if anyone here has any thoughts.

Thanks. 

[kitbash1]

Sorry to say this, but your going to have to cut it. Putting it in the freezer isn't going to help. just bite the bullet and cut it. and next time use more release agent.

[jeffb]

[Greg Wann]

http://smcbofphx.proboards.com/thread/1467/mclaren-m8b-tires

Hi David,

  Here is a link to some tires I made some time ago.  You should find plenty of casting help on this forum.  So anyway, You will need to imagine when you are looking at the right hand mold half that the master tires are set on these posts that are sticking up and that when the mold was first made the part on the right was all clay.  I'm not very good at keeping up with photos to document the progress of a project.  So what happens is the tires are very nicely made but can be a bear to remove from the mold.  Make certain that your mold release is compatible with your silicone.  If your mold release contains silicone then it might be acting as a primer to actually cause the two parts to stick together.  So, if you are new to casting or are switching products be aware of such problems.  I started using Smooth-On products.  I can just go 15 minutes from my work at ASU in Tempe and pick up product fresh off the shelf, that is very handy.  I switched to using their mold star 30 silicone and was having tons of problems!  I switched to using MANN 200 mold release.  The temperature of your room is very important, 76 is a pretty good temperature.  If your silicone is stored in a room to warm and you pour in the same room your mixed silicone could start curing before you get it in your mold box.  I pressure cast and I have a vacuum chamber and pump to de air silicone and resin.  Humidity can be a real problem too, resin can draw in unwanted moisture.  If you mix and pour resin and it foams up, you have a real moisture problem.  Resin kicks and cures at around 160 degrees.

[Art Anderson]

FWIW, in the ten years I was resin-casting (several thousand molds over those years, BTW many hundreds of thousands of castings from very small to complete car bodies), I used but one mold release when making new RTV rubber molds, and that was plain old Vaseline petroleum jelly, well-thinned with Testors enamel thinner!   Basically my mold release was made by dissolving about 1/2 teaspoon (by eyeball) of the petroleum jelly in 4 ounces of the enamel thinner, stirring and shaking the stuff (with a lid on the jar of course!) until the Vaseline was completely dissolved.  It NEVER failed me, and NEVER caused the first problem with even the very first castings of of new molds made in this manner.

Art

[Dave Van]

I use a coat of Vaseline between pours......always works.  You'll have to cut it apart now.

[bill w]

What Dave and Art said. 

[GerN]

Yup, good old Vaseline in mineral spirits works great with the Permatex red RTV I use for molds, and I just made two semi-two part molds by partially splitting a fully encasing one part.  V and min sp (I hope) will allow these molds of full Corvair engines to be used over and over.  You might use a fresh blade to separate your mold halves.