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low cost alternative for some RTV silicone applications

 
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Fredo
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Joined: 21 Mar 2007
Posts: 251
Location: Kingdom of Nye Area 51

PostPosted: Wed Jan 07, 2015 11:11 am    Post subject: low cost alternative for some RTV silicone applications Reply with quote

Found this on Alloy Avenue... Funny how little gems of information just pop up.... I'm off to buy a tube of silicone sealant... I've got several small things I need a mold of....


Ok there is a bit of a story here first...
A few years back I worked at the local museum here. They were building some dioramas of the local aboriginal people as they lived centuries ago. The one diorama was a fish camp. In this camp they needed a pile of caught fish and a pile of fish being cleaned including the internal organs of the fish. They had live fish which they speared and stacked, then froze them. Same with the cleaned fish and fish guts, also frozen. They were not casting these in metal but in polymer resins and such, but the molds interested me.
They did not use RTV silicone, which here is kind of pricey. The stuff they used cost less then 1/4 of the cost of RTV. Plus the frozen fish were molded and placed back in the freezer for the mold to set. This product will set at room temperature or even in a freezer. All the details of the fish were captured in the mold. The product is simply washed silicone sealant/caulking.

Not that this will replace every application of RTV silicone, it does make a robust silicone mold, on the cheap.

Here is how you wash it. This process is very smelly, like very strong vinegar. Good ventilation is highly recommended.

Get 100% silicone caulk in the application tube. What we will be doing is washing out the chemical inhibitor they add to the silicone to stop it setting in the tube. Cut the end off and push the entire contents into a 5 gallon pail with 3-4 gallons warm water and a couple drops of dish soap. Gently knead the blob, under water the whole time, stretch and squish it to effectively wash out the inhibitor. You will feel it start to get stiffer and lots less gooey. Try not to fold the blob and trap water pockets in it, as this is not desired.
Now remove from the water and apply to the piece you are molding. If your form is solid just press the silicone into place and let it set up. I do use a silicone release spray on my model, and that should be mentioned.

For plastercine models, I freeze them and they are then solid and I can mold them without damaging them.

I cut my piece out of the silicone mold, but I do make a 2 part plaster casing, first, that will hold my mold closed when filling. So if I cut out the silicone mold, say, North-South, then my casing will split, East-West. I cut my silicone in a sort of zig zag pattern cut on several angles, with a hook blade razor knife. This helps the mold want to fit back together with minimal slip or distortion later.

I thought I would share this info as there may be a time when you want to make a wax of something, like an Ice Sculpture, and this would be the way to do it. Did I mention it sets in a freezer?
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IMMark
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Joined: 18 Nov 2010
Posts: 189
Location: Columbus, Ohio

PostPosted: Fri Jan 09, 2015 10:00 pm    Post subject: Reply with quote

You are always coming up with interesting and useful tips!
As always thanks for sharing.
Mark
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