playing with silicone

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NewLondon88

NewLondon88

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Joined
May 15, 2008
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Tried out some silicone RTV this weekend and I must have mis-read the
info online, I thought it was pourable. I figured that would help it flow into
the undercuts and pick up good detail.

I got a small bottle of the blue activator (Part B) and part A looked like a
bucket of Marshmallow Fluff. It was about the same consistency, too.

I knew it wasn't going to be so easy when I got a plastic cup and dipped it
into the bucket to pick up several ounces.. it wouldn't flow into the cup.
I got a popsicle stick to push a glob of it into the cup, but when I pulled out
the popsicle stick, it took the glob back out with it. Strange stuff..

It did thin out a little bit once I got it mixed, and it reached a
semi-pourable consistency. But it was full of bubbles. I put it into the
vacuum pot for a few minutes (no clear top, so I wasn't sure how long
to leave it in there) but it didn't seem like it expanded. I'm only going by
how much residue was on the sides of the container and it didn't look like
the level rose much, if at all.

Poured one small mold as a test, we'll see how it comes out. The pour was
full of air, looked like pancake batter. I might just go back to the urethane
RTV. It needs a release, but mixes 1:1 and pours. We'll see...
 
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CaptG said:
Charlie, just curious, what are you trying to do with the silicone? I must have missed something somewhere.
Click to expand...

Ah .. making molds. I went into the shop this morning to check it out and
the mold came out perfect. But boy, it is strange stuff to work with.. :eek:
 
The first time I used blue silicone, many years ago, I was making a mold of a low relief wood carving, the original was carved out of sasafrass with long end grain pores. It was so thick that when it was in the pouring form I had to push it all around with a toungue depressor just to get it covering everything. By the time it cured hours later it had settled down nice and smooth. When I removed the wood carving the mold looked like it had whiskers from all the places it ran back up into the pores of the wood. The visible viscosity is like mashed potatoes but if you give it an hour it will probably drip through a coffee filter.
 
Skye, you're the only guy I know who would order one with that outfit.
You skip the nightie and mini skirt, but you order the safety goggles and
respirator.

Chasper, I don't know if this will ever pour, the viscosity doesn't seem to
go lower than the initial 15,000 or so. But you're right about it flowing.
I figure I'd never have to copyright a mold .. this stuff picked up my
fingerprints in the Vaseline that I used as a release..
 
Hey Charlie! Great minds think a like. I'm trying to get some silicon down here to make some moulds, so I came here for advice, and find you're doing the same thing!! We seem to be in sync, except you have more time to play tham me :worship:

There's like 15 different silicons to pick from at Barnes, I have no idea which is best. So confusing.

So what did you use as the former for the mould? Care to show us a piccie?

Russell.
 
PenAffair said:
Hey Charlie! Great minds think a like. I'm trying to get some silicon down here to make some moulds, so I came here for advice, and find you're doing the same thing!! We seem to be in sync, except you have more time to play tham me :worship:

There's like 15 different silicons to pick from at Barnes, I have no idea which is best. So confusing.

So what did you use as the former for the mould? Care to show us a piccie?

Russell.
Click to expand...

For the master (original/positive) I carved it out of EOS. That's like Corian,
only it's 1.25" thick where I get it. Kitchen countertop makers have tons
(literally) of it sitting around from where they cut out the double sinks.
It's expensive, so they don't want to throw away the scraps.. but they
can't really do much with it, so they're happy to have it go to someone
who can use it. Usually free .. or a case of beer, and you can walk out
with several hundred pounds. It's nice, polishes to a gloss and it makes a
nice master. Put a good finish on the master to help extend mold life.

For the RTV, I used either urethane RTV or Tin-Sil 70-25 from Polytek.
The Tin-Sil is silicone. The urethane mixes 1:1 and easier to work, but
doesn't look 'pretty' like the silicone, and it needs a release. Actually, BOTH
should use a release to extend mold like.

ps.. not much time to play here, either. I've had the stuff for weeks and
just managed to get out a couple of molds..

Get your pressure pot tuned up, get a vacuum pump and it isn't a bad
idea to pick up an ultrasonic cleaner somewhere. It helps. But the vacuum
pump is a must for silicone

I don't have pics yet, I'm still working on prototypes and I have two
people testing them now. They'll try them out and either tell me to give it
up, or they'll tell me how to adjust/refine. Once I get some feedback, I'll
get some pics.
 
Last edited:
Charlie,

Degassing is necessary for some silicone's but not all. I buy my RTV silicone from GT Products ( http://www.gtproducts.com/ ) I talked to Kevin there and have used 2 different silicone products neither of which needed degassing (vacuum). The were pourable, strong, flexible and exactly what I was looking for. I've made molds from tiny inlay's to large volume multi-blank's. It really is a good idea to "pick the brains" of the tech's. There are so many products out there that sometimes two or three words to the tech will change his focus. It is then a great idea to do as you have done and share your experience with others.

Take Care,
 
Hmm,

I was hoping I could go without vacuum, as I have nothing that sucks.....

I have some Maximould coming. My other option was Tin Sil 70-30, which a supplier in Aus has and on special at the moment, but their postage was more than the maximould, so it was marginally cheaper.

Russell.
 
Haven't checked too far. Some have mentioned those food vacuum sealers - not sure how much vacuum they pull though, not that I have one of them either. I remember some venturi things to go on your pressure pot, which would be the best option, but I think that was in the US as well. The other problem with them is you can't see what's happening inside the pot, so don't know when to stop.

Russell.
 
PenAffair said:
Haven't checked too far. Some have mentioned those food vacuum sealers - not sure how much vacuum they pull though, not that I have one of them either. I remember some venturi things to go on your pressure pot, which would be the best option, but I think that was in the US as well. The other problem with them is you can't see what's happening inside the pot, so don't know when to stop.

Russell.
Click to expand...

I can't see in mine, either. But I'd think it happens in the first minute or two.
And then you leave it another minute or so.
Since the TinSil has an open time of about 30 minutes, I just put it in the
vacuum and leave it for 5 or 10 minutes while I do something else.
 
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