Champagne bubbles - not so desirable in a two part resin casting...


Active Member
So I was VERY rusty as far as molding goes - I over-did the release in my silicone mold. Still hoping to save the cast, though in three places I have champagne bubbles - so fine! - in the surface. I sanded it down so now I have lots of tiny bubbles that need filling. I'm looking for a less-stinky (than Tamiya) or even home-made filler that would work. It's the first from the mold and I would like to keep it as a mother for the next round - the original broke when I had an issue getting the base out. (I know, I know - see above re: rusty). I was using Smooth On 325. Heard something like mixing white glue and powder, or even wood filler... ideas?
I use acrylic Gesso and I mix in cornstarch to thicken it and schmeer it into the holes. It may take a couple of applications but it’s safe to use, just seal it with future or the finish of your choice before you pour RTV on it. You can also use super glue and cornstarch.
When you make a casting you can dust the mold with, again, cornstarch- brush a pile around the cavity and then tap the mold to dump out the excess, this will leave a nice coating that will release the resin and get rid of moisture in the mold. I find it works better for me than spray release-but if you plan on making a lot of castings the spray release will extend the life of the mold better than the powder. Hope this helps!
Yep, I was going to recommend baby powder and CA. The only down side to that method is sometimes the CA mix is harder than the surrounding resin, so sanding can be a little tough.
True! If you fiddle around with the ca and cornstarch/ baby powder, you can vary the hardness. Less powder makes it carvable like styrene and sets slower, more powder becomes harder and sets faster.
Another way to fill this holes is to use a thinned down Magic Sculpt. As you mix the two parts add a couple of drops of water at a time until it gets pasty in texture. It sets a bit slower and gives you more time to work it. This works with other brands of epoxy putty as well
not much of a help to your situation, but as far as release agents go, I apply a coat of talcum powder with a small paint brush and then use my air compressor to blow off any access out of the nooks and crannies. I NEVER use the spray-on stuff... Maybe I just haven't found the right method/product but every time I try ,I end up with a surface that looks similar to an orange skin. If the mold is not too complex, sometimes I forgo adding any release agents completely.

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