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Making a LARGE silicone mold??

I wasn't sure where to post this but.....

My mom is trying to make a large (10-12" wide/3-4" deep) silicone mold and she's running into the silicone drying before she's even finished pouring it out (like after 30 seconds). Does anyone know of a product or technique that would work? Or even a website with tips someone could point me to?

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I know it's a long shot but I figured if anyone knows it would be my fellow etsians!
Yes. I have made molds and cast items as large as the liberty bell.
I'll convo you, thanks. :)
Sorry. Took an ambien about an hour before that post. Don't remember typing it. HA HA, spose I'll go check the car for dents and face-prints.


There's not a lot to start with here, so ... some questions.

You say you need to make a mold about a food square, does that mean we are copying something that is mostly flat? Like a plaque? Or will you need to reproduce all sides of it?

What is the pattern (thing being copied) made out of? Not a huge deal but can eliminate a step.

What is the material that will be poured into the finished mold?

How many castings will you need to make out of this mold?

It sounds like your mom is using a 2-part silicon mold material? If so, they can be dodgy for large pieces. Often this kind of mold can be applied a little at a time so you could work in smaller areas. I would be hesitant to try this, it seems like a recipe for a weak mold.

If you only need to make a single reproduction, I would recomend an alginate molding material. You mix it up and pour it all at once. Wait 5 min and pull it off. The detail it captures is remarkable but it's a one-time use and you have to use it pretty quick.

Try this:
1- Go to home depot and get 2 or 3 caulk-gun tubes of 100% silicone. Don't get 'fast-drying'. It should be clear and about $6 a tube.

2- Fill a larg-ish bowl or bucket with a couple gallons of tepid water.

3- Add some basic blue dishsoap to the water until the water color is also good and blue. Hard to mess this part up except by not using enough soap.

4- Pump all of the silicon from the tubes into the soapy water.

5- Fold a coat hanger in half then in half again and stick one end into a power drill to make a wisk.

6- Blend the silicon and water for 2 minutes.

7- Using your hands, reach into bucket and 'ball up' the silicon. It doesn't disolve in water but it gets shredded by mixing so you reform it into a wad of slime.

8- Pull it out of the bucket and lay it down over the part to be copied, working it into the detail.

9- From here you have a 5 minute wait for it to set then maybe an hour or so to fully cure.

**- instead of soapy water, coleman camp fuel or mineral spirits works a little faster and maybe better results.
ArtificerMade - wow I have never heard of that for a home made silicon mold!
And I have worked around molds for 20 years. Of course I live by all of the distributors for plastics as I am right near Hollywood and all we do is make molds for puppets, movie effects, costuming, make up......
But that is DIY awesomeness!
Had to mark this.

And my own little DIY tip.
KY Jelly is awesome mold release!
Thank you!!
I have been expanding on some of the work done by others over at instructables .com.

Here is what is happening (to the best of my understanding):

Silicone like many polymers (like rubber) needs to Vulcanize before it will do anyone much good. Vulcanization links the strands of polymers together which hardens the plastic up a bit and makes it much stronger.

Vulcanization of rubber is often done with heat and pressure. The rubber you make a jewelry lost-wax production mold out of feels like cohesive modeling clay until you press it and heat it up for a bit.

But vulcanization can also be done with chemical treatments. So you have a polymer resin and you add a hardener to it, you are changing the nature of the resin in a way that makes it harder to some degree, stronger, more useful.

When you want to do this without mixing 2 things together though ... now what?

This is what we call Room Temperature Vulcanizing (RTV). You squirt the latex , or silicone, or polyeurythane or acrylic onto something and wait and eventually it hardens right up.

To do this the manufacturers dissolve the hardener in a solvent. The solvent must be something that will not affect the resin. Then they mix the solvent-hardener with the resin (silicone or whatever) and package it in a sealed tube.

When you squirt it out the part-A and part-B are already thoroughly blended but because part-B is disolved in a solvent it cannot harden the part-A.

But out in the open air... The solvent evaporates (which smells bad) and the part-B does not. Presto! Now the mixture can harden.

Long story short... The dishsoap/camp fuel/mineral spirits/ separates the solvent from the part-B which allows it to evaporate faster.

Okay, I'm done. You all can wake up now.
wow, what great info. Makes me miss the 'Techniques' section :(
'Smooth on' for pourable molding materials, they have many different types with different qualities for different types of projects, with long working times.


For something so large, if you want awesome detail, a brush on is usually done I think, unless there's really zero undercutting.
Holy carp fish! Thanks for posting that Christopher Bright! I wonder if I could make it up in a smaller amount to mold doll heads??

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