Silicone won't solidify, can we salvage it?

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CharlesHouse

Active Member
We tried to make a mold of a prop gun and used Crayola clay, having read it was non-sulfur. Being cold in our apartment, it took a while to solidify but the top eventually did overnight (Smooth-On Mold Star 15 Slow). However, when removing the clay, it seems that the under part of the mold is still not solid. I assume it is from the clay. I am wondering if we can use a razor to cut the mold where it wasn't in contact with the clay and use it for another attempt. This mold took probably half a gallon of silicone, so it's pretty costly to screw it up. We had a hard time finding clay in any quantity that wasn't stupid expensive, but I ordered some Van Aken Plastalina so we can try again.
 

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robn1

Master Member
That should work, if the Moldstar will bond to itself. Some silicones do, some don't. Try a test, mix a small batch and apply it to the cured mold to see if it will bond.

Also, let it sit another day or two to see if it will cure. I've had trouble with platinum silicones, including Moldstar 30, curing slowly against certain paints. It cured through but was still gooey against the master, but cured completely after 72 hours.
 

MustangGTR1

Well-Known Member
Also try a hairdryer to speed it up. You will also run into trouble if you use platinum against tin based
or
 

sa maker

New Member
I have a couple of questions if you don't mind: How old is the silicon? Are you sure you mixed the correct proportions of catalyst to base? (I'm sorry that sounds like a very basic question like "Are you sure the power switched on.")
 

CharlesHouse

Active Member
That should work, if the Moldstar will bond to itself. Some silicones do, some don't. Try a test, mix a small batch and apply it to the cured mold to see if it will bond.

Also, let it sit another day or two to see if it will cure. I've had trouble with platinum silicones, including Moldstar 30, curing slowly against certain paints. It cured through but was still gooey against the master, but cured completely after 72 hours.
It is supposed to; I read about people cutting up previous Mold Star pieces to add for mass into new ones.

The gun was covered in clay, and the barrel was filled with it, so it was messy. I took it in the shower with a tooth brush and tried to brush away the clay so that, if it were going to cure, it would. I need to remove the clay from the barrel and fill it with new clay.

I have a couple of questions if you don't mind: How old is the silicon? Are you sure you mixed the correct proportions of catalyst to base? (I'm sorry that sounds like a very basic question like "Are you sure the power switched on.")
The silicone is brand new, got it last week directly from Smooth On. As far as I know, yes, the silicone mixed fine, as maybe two inches of the mold cured fine, while the surface that was against clay is still sloppy, though the registration keys we made are still holding form even when the surface is messy, which suggests that the center of the keys is solid.

If it doesn't cure, we are considering taking a razor and scraping the uncured section from it and using what we can. This side of the gun used around half a gallon of silicone, which is pretty expensive to do.
 

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