# Silicone Caulk for molding?



## Sytnathotep (Oct 10, 2011)

Heya Peeps! 
I know someone was talking about this in an old thread not long ago, and I remarked that I was going to experiment with this. For the life of me I can't find/remember the thread now, so I guess I'll start my own.

Anyhow, the experiment!

Basically I have this tutorial a try. My goal is to mold a small pie pumpkin with this method, and see how it holds up in my opinion to real mold silicon like Dragon Skin.

So! I did as recommended and in small amounts, mixed up the silicone caulk with the corn starch. Too things I found out immediately. One, is that it is really difficult to mix, so instead of doing what I did, I would recommend mixing this up in a small plastic bowl or Tupperware, as it will wreck a Dixie cup, and use a metal butter knife as opposed to a wooded craft stick, you will break the stick!

The second immediate observation is the smell. The tut says it will give off a strong vinegar smell as the curing creates acetic acid, and that you should do this in a well ventilated area. This is no understatement!! For the most part, I didn't really smell anything, but if I got my face too close, or the breeze was just right, it would almost knock me on my ass! I thought it was bad being around when my wife cans pickles, that can't hold a candle to this! So for goodness sake, open the window! lol

Anyhow, once mixed up I smeared it onto the pumpkin. This stuff is umber tacky and about the thickness of peanut butter. It took a whole 10 oz tube and a bit of cornstarch to cover the entire pumpkin. ( i didn't use near as much cornstarch as the tut says, it is plenty thick enough as is!) Because of the thickness, I'm not sure how well the details will show up in the finished mold, but I can really see this as being a great second-third layer coat to a mold with a thinner first layer.

I am waiting for this stuff to set up right now. Once it is cured, I'll see if I need another layer, and how hard it will be to get off the pumpkin. So, here is a pic of it now, and I'll update once it is cured how it turned out!


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## Lord Homicide (May 11, 2012)

Well... I'm in and thanks for the smell heads up. Following. heh


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## Sytnathotep (Oct 10, 2011)

Well, checked in on it a while ago, and it is already cured! That certainly didn't take long. I was able to remove it easy enough from the pumpkin turning it inside out, but it ripped a little around the stem. (may have been my mixing) also i see that it doesn't quite rebound back to its shape, and gets stretched out a little. Will try to patch it and then cast it.


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## Bone Dancer (Oct 7, 2005)

About how much corn starch to one tube of silicone ?

http://www.hauntforum.com/showthread.php?t=27130

I think this is the thread you were looking for.


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## billman (May 3, 2006)

Nice! Do you think for mixing using an electric hand mixer on low speed would work? or would it make it cure faster?


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## Sytnathotep (Oct 10, 2011)

Lord Homicide said:


> Well... I'm in and thanks for the smell heads up. Following. heh


Be prepared, it will knock your socks off, or at least mine did. lol



Bone Dancer said:


> About how much corn starch to one tube of silicone ?
> 
> http://www.hauntforum.com/showthread.php?t=27130
> 
> I think this is the thread you were looking for.


Yes! Thats the one. 

As I didn't measure first I'd guess it was about 1/2 cup silicone to around 1 teaspoon of cornstarch that I like the best.



billman said:


> Nice! Do you think for mixing using an electric hand mixer on low speed would work? or would it make it cure faster?


As tacky as this stuff is, and the fact that as you mix it, it sticks together and to the mixing tool. (like bread dough on a dough hook) I bet you'd be spending more time trying to get it off the mixer beaters.

Second coat I just put on, and using a small tubberware and a cheap metal butter knife made all the difference in the world, much easier to mix and apply. (see pic)

I've recoated the entire mold, and once that is cured, I'm be figuring something out for a mother mold.


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## Lord Homicide (May 11, 2012)

How did the mold hold up?


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## Sytnathotep (Oct 10, 2011)

Lord Homicide said:


> How did the mold hold up?


The mold is done, I just need to make the outer support mold. I thought I'd give the shell shock one more try, and it failed pitifully. (Broke to pieces just taking it off) so I guess I'll do the tried and true plaster method, as I can't afford anything else at the moment. lol Once that's done, I'll update and post some more pics.


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## Bone Dancer (Oct 7, 2005)

Thanks for the updates. Looking forward to your next posting.


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## Bone Dancer (Oct 7, 2005)

Sytnathotep said:


> The mold is done, I just need to make the outer support mold. I thought I'd give the shell shock one more try, and it failed pitifully. (Broke to pieces just taking it off) so I guess I'll do the tried and true plaster method, as I can't afford anything else at the moment. lol Once that's done, I'll update and post some more pics.


Any up dates on this project?


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## discozombie (Jun 21, 2012)

anything new on this, im curious....


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## Lizzyborden (Sep 7, 2012)

Curious too as I'm wanting to try this. I don't have a heated work area and don't want to deal with the smell inside, so I'll have to wait for a warm sunny day to try it outside.


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## Sytnathotep (Oct 10, 2011)

Peeps! Hope your having a horrible Easter!

Sorry for the long delay in replies. With Holidays, and now spring sprung ( I have a 50ft greenhouse I'm practically remodeling lol) , I haven't worked on props. 

I can tell you this, the acid in the caulk will desolve a whole pumpkin into a puddle if left in contact! I've had this project sitting on my workbench since it began, and some time ago I thought I'd have a crack at it again, only to find pu'kin paste all over the place! I'll now have to improvise and stuff the mold with something else to keep its shape in order to make the outer mold support. Its way too floppy to attempt to caste with out some outer support.


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## heresjohnny (Feb 15, 2006)

I finally had a chance to give this a go, using the corn starch method, and want to share the results. I am building budget cemetery fence and wanted to use the larger ghoul head for a post topper, and the smaller skull heads as finales.










I used about a 1:1 mixture of silicon and cornstarch. I found that it mixed quite easily with a consistency of silly putty. I mixed it with half a tube of silicon at a time, and managed to get one full mold per tube. I made the molds thick, and used a small wooded box for support because I was planning on using great stuff.










The molds seemed to turn out well, but keep in mind this is the first time I have ever tried casting. I thought with small casts I could use great stuff, however even with the smaller items, they shrunk as they dried.










Now I am trying mache clay. If that works I will probably make another set of molds just to speed up the process, I need at least 50 casts.


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## discozombie (Jun 21, 2012)

I think they look great. I used great stuff to cast and found it shrinks as well. I like the effect the shrinking took on the small skull. I also cast with mache clay pressing it into the mold. Not sure on the weather in your area but Ive given up on mache and the outdoors.


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## heresjohnny (Feb 15, 2006)

discozombie said:


> I think they look great. I used great stuff to cast and found it shrinks as well. I like the effect the shrinking took on the small skull. I also cast with mache clay pressing it into the mold. Not sure on the weather in your area but Ive given up on mache and the outdoors.


Yes, I have read your posts on Mache and mice

I live in central Florida, so humidity, mold and roaches are all challenges. I have found that sealing the finished pieces well with polyurethane works well, you will find out quickly if you missed spot.

Pulled the first mache pulp casts, I like the result, looks like pitted metal. Second set is cast, this time I am trying to stay thin with the pulp to decrease drying times.


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## heresjohnny (Feb 15, 2006)

That was fun, it was like a cross between making minions and playing face-off. 21 pulls of plaster of paris casts for 42 small skull heads, and 5 larger casts with paper mache casts, 3 to go. The silicone/corn starch molds held up well and are still working.


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## RoxyBlue (Oct 6, 2008)

OMG, an army of skulls!:googly:

I'm impressed by your productivity.


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## Sytnathotep (Oct 10, 2011)

That is very good to know Johnny!! I still have that poor pumpkin mold on the bench..lol I need to give this a go, and I have more skulls to mold also. Did you use a support shell for any of these molds or did you just pile the silicone up thick enough? How much caulk would you say that you used?


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## heresjohnny (Feb 15, 2006)

Sytnathotep said:


> That is very good to know Johnny!! I still have that poor pumpkin mold on the bench..lol I need to give this a go, and I have more skulls to mold also. Did you use a support shell for any of these molds or did you just pile the silicone up thick enough? How much caulk would you say that you used?


Details are a few posts up, I tried to build a mold without support, and the silicone would relax and fall away from the skull. I built a small box to constrain the silicon initially because I planned on using great stuff, but the box ended up being ideal to hold the silicon mold in place until it dried, and holding the mold halves together during the plaster pour.


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## Bone Dancer (Oct 7, 2005)

Thanks guys for all the info. I have tried silicone before and it was a disaster. The 1:1 corn starch/ silicone looks like the way to go and with a box to hold it all together.
Those plaster skulls look great.


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## Sytnathotep (Oct 10, 2011)

Thanks again for the info. I have In-Laws staying visiting this week and raining on my prop building parade., but as soon as they are gone I'm going to give this a go again, I'd love to see how This would work with Foam-it.


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## Sytnathotep (Oct 10, 2011)

Ok, so i finally got back to this today after what? Years? Lol

I made a support for the mold by filling a cardboard box with expanding foam, then cutting the whole thing in half. I cast the first pumpkin with foam-it. Had to split the mold down the side to get it out, but not too bad! I'm going to try to see if i can get a hallow cast next to carve next.


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## heresjohnny (Feb 15, 2006)

I just cast another 20 pulls from the silicon molds I made last year, still holding up very well.


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## Sytnathotep (Oct 10, 2011)

While this is its first pull, its held up well for now being 3 years old! lol


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