Silicone Caulk Mold Tutorial

Kwally89

Hunter
Here is the mini-tutorial that everyone has been asking for!

MOLDING WITH SILICONE CAULK

Ok, so you are poor and want to make a quick mold of your sculpt/prop. What do you do? You use silicone caulk. Yes the same stuff that you use in the bathroom around sinks and showers.

Some people will tell you to mix in some glycerin or paint. Others say that you need to put some plaster in it. My method is A LOT easier and works just as well if not better. Ok, silicone caulk cures with water. When you squirt it out of the tube, it instantly begins reacting with the moisture in the air to become solid when cured. People have used plaster mixes to speed this process up because the silicone caulk produces acetic acid while curing. Acetic acid mixed with the mild base (usually a carbonate) in certain kinds of plaster produces water and a salt. This is obvious to anyone who has taken a general chemistry course...like I already stated, this is true, but is only need if you are casting something with the silicone caulk. In a simple mold, it is unnecessary.

MATERIALS

100% Silicone Caulk: I prefer the use GE Silicone 1 TRANSPARENT. I usually get two tubes, but it will differ depending on the size of your piece. In this tutorial, I used white silicone because they were in the transparent bin at Wal-Mart so I thought I bought transparent!
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A medium to large bucket

Some dish soap

a fairly sharp knife

silicone/grout dispensing gun

Procedure

First, you need to take your trusty bucket and fill it with luke warm water. As the water is coming out of the faucet, squirt about...idk...the volume of a golf ball or more dish soap into the stream. This just makes the dish soap mix and gets the suds going.
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Next, place the bucket next to your sculpt. Cut the ends of the silicone tubes off.
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It is beneficial to do this because it is hard to get a smooth surface if you squeeze all the silicone out in little snakes.

Squeeze ALL the silicone into the bucket. Stick your hands in the water and get them soapy and wet before working the silicone. The soap acts as a nice release from your sculpt and your hands. The only problem is the silicone has a hard time sticking to itself. Hence, my suggestion to cut off the ends so you don't have a bunch of little silicone snakes.

Work the silicone A BIT under the water. You don't need to play with it though it is fun. Grab the big glob out of the water and get it into a ball or pancake shape. Make sure the surface of the silicone is fairly flat. You don't want to capture any air bubbles.

Push the silicone over the sculpture making sure that you work it into the undercuts and detail areas.
IMG_0260.jpg


If I would have realized the bins at Wally World were marked wrong, I would have used transparent. You really need to use transparent so you can accurately judge the thickness of the mold. Generally, a thickness of 1/4" will work just fine. I actually don't even make mother molds when the silicone is thick enough because it will hold its shape. With that being said, that means that the silicone doesn't have the ability to stretch very much before it rips.

You should be able to demold anywhere from 24-48 hours though it will dispel the acidic gas for 1-2 weeks. I usually get really excited and demold in 24 hours. If you got enough water in there and it isn't too thick, you should be just fine.

Any questions....feel free to ask!!!

HAVE FUN!!!

Kody
 
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Sticking with the frugal builder theme, I decided to make the mother mold out of expanding foam.

DOW's Great Stuff really is great stuff! Pun intended...wow lame!
foam.jpg


Obviously, it wont get a nice forming mother mold, but I just needed to hold the curve of the Nihilus mask. You can try to spread it on, but it is difficult so try to spray it nicely. You can also mist it with water to speed the curing and make it expand less.

foam2.jpg


Demolded
mold.jpg


I slush cast a prototype with smooth cast roto....that I opened 13 months ago!! Needless to say, it is very old and should cure bad. I have found that this stuff will work for A LONG TIME. Since I spent $10 on molding supplies, I wasn't going to use my good smooth cast! That would be fiscally irresponsible! For using silicone caulk, expanding foam, and 13 month old urethane, it looks pretty nice! Just dremeled the eyes out quick and lightly sanded.
sandedmask.jpg


ENJOY!
 
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OK I have a question... I got lost in the second post. Why the foil? And where do you place the mold, under the foil and then spray the urethane over the foil? I am just confused because what is the cast made out of? The silicone or the urethane??
 
The first layer is done with caulk, then to give enought strong to the caulk he has add the urethane, but the urethane sticks on the caulk so he add the foil with the objective to not have the urethane sticked on the caulk.

Do I explain?
 
Ok, the silicone caulk is ONLY the mold. You can cast with it, but you don't want it to be too thick. It just wont cure right. I placed tin foil over the silicone mold just to use as a barrier between the mold and expanding foam mother mold. I then took it all off the sculpt and cast the urethane directly in the caulk mold. This is all standard molding and casting, but I used non-standard materials (caulk, great stuff foam, etc.)

Kody
 
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Alright, makes sense. Thank you for answering my question. But one question of mine was unanswered... The final cast is made out of the urethane? Thank you.
 
Alright, makes sense. Thank you for answering my question. But one question of mine was unanswered... The final cast is made out of the urethane? Thank you.

Yep. As I said while answering your question, I cast the urethane directly in the mold and slush cast it. Just means that I slushed the urethane around to evenly coat the sides of the mold. Smooth cast roto is a thixotropic urethane meaning that it self-thickens before it gels. That allows you to build up a layer on the sides of the silicone mold. Hope this helps! :D

Kody
 
The urethane, how much does it cost? I really like this tutorial and will definitely use it in making my Iron Man helmet this summer. My favorite thing about this tut is that it's cheap. If urethane is expensive, is there something I can use that is cheaper but will still come out nice? Since you said the molding materials cost you $10, I'd like something under $5 to cast with. Thanks.
 
The urethane, how much does it cost? I really like this tutorial and will definitely use it in making my Iron Man helmet this summer. My favorite thing about this tut is that it's cheap. If urethane is expensive, is there something I can use that is cheaper but will still come out nice? Since you said the molding materials cost you $10, I'd like something under $5 to cast with. Thanks.

You can use anything to cast such as plaster or hydrocal. You can get a nice amount of plaster at Hobby Lobby for around $5. I buy 30-40lbs of hydrocal SHIPPED (shipping will kill you on heavy mold making/casting materials...even clay) for about $35-40. It is a lot, A LOT better than plaster.

Kody
 
It's ..... so ...... PERFECT!!! This tut will REALLY help me when I do my gauntlets.

THANKS!!!


How does the plaster stack up against, say, a urethane plastic, or even resin???
 
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