What am I doing wrong? (Ultracal 30 molding problem)

stopmo said:

On my last two ultracal 30 molds of chavant clay sculptures I've had issues with the surface detail coat. I get tiny air bubbles on the surface. The latex castings come out with very, very small pimples over large surface areas like you would see from mold erosion but these are the first pulls!

I try my best to do the detail coat right, I make the plaster very thin and brush it on with a chip brush to avoid air pockets but I'm wondering if this is my failing. Can the detail coat be too thin? Can brushing on the coat introduce air?

Any ideas would be greatly appreciated, I'm preparing for my next mold and want to avoid any problems.

Thank you

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Jediknightandy said:

hi! I had a similar issue with some of my first mask castings, I was using WED clay with a coating of a wax release agent. When applying the plaster I found that it didnt want to spread on the surface, instead it formed watery beads on the sculpture, this is due to the water based plaster not being able to cling to the oil based surface. Chavant is oil based so you will get the same result. This reaction traps airbubbles on the surface quite a bit, my Mangalore latex mask has many many pimples on the surface that I needed to snip off.

Solution I found that worked was to give the sculpt a heavy dusting of Talc powder, this will give the plaster something to grab onto and it breaks the surface tension of the water in the plaster so it flows better. Then use a combination of flicking the plaster on the sculpt with your hands, and then use an airbrush to chase out airbubbles form the thin layer of plaster. I didnt have an airbrush that I would allow to be covered in plaster during this process, so I found that blowing into a long drinking straw worked just as well to eliminate airbubbles (though its hard on the lungs!)

It took me a few masks to get the clean surface I wanted, so just keep practicing, you will get there!
Hope that helps!
Andrew

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If the splash coat is too runny, it wont adhere right to the clay/sealant. I use crystal clear and it works fine. Dont make it TOO thin though, also, get a straw and blow it into the really detailed parts, and I also like to vibrate the sculpture a bit if I can to get out any other trapped air bubbles. If youre short of breath a can of compressed air would work too. Shouldnt be too much of a problem if youre casting in latex, thats pretty forgiving stuff. Slip cast or foam?

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