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apes3978
May 28, '07, 4:36 PM
I need help in regard to mold making...

The other day, I tried my hand at pouring a mold... I thought it was successful, as it seemed to "harden up" over night as the instructions said it would. I used a plastic cup to pour the ingredients into and I had to cut the cup as the mold didn't just slip out, but that was no big thing... I got the mold out of the cup and used an Exacto knife to cut a slit down the side to remove the master-piece and so I could use it as a mold... When I was cutting it, the sides and the top were very "sticky" feeling, but I thought maybe that was because the sides weren't exposed to air and I thought the top, being the top, might just be that way, but obviously it wasn't supposed to be that way... I went ahead and poured the liquid plastic anyway... It hardened up just as it is supposed to, but here's where things get messed up... The side where the slit was cut melded back together and I had to rip the mold apart to get the piece out... When I got the piece out, it was covered in rubber, and I'm having a very hard time cleaning that off, so I might just scrap that head... I recall asking someone about using the mold release, but they said they didn't use it, so I thought I'd skip that too... Overall, it's a useless mess right now...

I guess I need to know these things:

When I poured the mold making compound, should I have used release so the rubber won't stick to the cup?

When the mold making compound is poured and it's sat the recommended 16+ hours, then what do I need to do? I know I'll need to remove it from the cup or whatever I use as a container, but what then? What do I need to do to the rubber mold so it does not remain sticky?

How do I "cure" the mold so it is usable? I seen on the HAZ-MAT sheet that there were also a few tips, but I didn't really see anything that I could relate to what happened here... It did say something about "curing" a mold, to heat it to 150 degrees, but I wouldn't even know where to start with that? How is that done?

YANOULI
May 28, '07, 5:42 PM
I had this problem last week, it took me 4 attempts to cast a head and even then it wasn't perfect, that was even with using release agent. I think it was just a bad batch of rubber compound.

What are you moulding? you need to coat the inside of the plastic with mould release, as well as coating the master head you want ( use liquid, not the spray ).
Let them dry for about 10 minutes, you can mix up the rubber while this is happening, pour the rubber and let it cure ( I do mine in the evening so that it cures overnight and whilst i'm at work ). When i get home i remove the master from the mould.
put some more release in the mould, let it dry then mix and pour the plastic.

Dave Mc
May 28, '07, 8:55 PM
16 hours to cure! Holy crap!

Go to smoothon.com and get yourself some oomo25. Easy to mix, cures in about 90 minutes, and I've not had to use any mold release with it at all.

apes3978
May 28, '07, 10:02 PM
16 hours to cure! Holy crap!

Go to smoothon.com and get yourself some oomo25. Easy to mix, cures in about 90 minutes, and I've not had to use any mold release with it at all.

Yes sir, it said/says to leave it for 16hours... I mixed it just as directed and it was bad... As a matter of fact, I tried to take the other master head out of the other mold I tried making that same night and it was as bad as the first one!

The mold making compound I used is actually is a SMOOTH-ON product, their REO-FLEX 20... I think I might check out the stuff you mentioned though...

apes3978
May 28, '07, 10:06 PM
What are you moulding? you need to coat the inside of the plastic with mould release, as well as coating the master head you want ( use liquid, not the spray )..


I was trying to make molds of two things: One is a head from an actual action figure, and the other is a head from one of the model kits.



Let them dry for about 10 minutes, you can mix up the rubber while this is happening, pour the rubber and let it cure ( I do mine in the evening so that it cures overnight and whilst i'm at work ). When i get home i remove the master from the mould.
put some more release in the mould, let it dry then mix and pour the plastic.


What you described above is what I was hoping to do... I figured it'd dry overnight and into the next day so I'd have a usable mold when I got home... Didn't quite work out that way though...

ctc
May 29, '07, 4:21 AM
Hmmmm....

Sounds like you had either a bad batch of rubber, or didin't mix in enough catalyst.

I use GI1000 silicone for my molds. Works really well, makes tough molds, easy to mix. (I usually err on the side of more catalyst when mixing it up.)

16 hours isn't too bad. The stuff I use takes 30. I purposely buy silicone with a longer curing time; allows for more air to escape. Useful when making molds of things with a lot of fine details.

Don C.