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Plaster/Silica Mixtures for Mold Making

This is part two of a multi-part series on using mixing plaster and silica for mold making.  Click here to go to the beginning of the series.

To mix a plaster and silica investment, it's important to start with a clean container. Using a container that has not been thoroughly cleaned may contaminate the mixture or cause it to set up more quickly than desired.

There are many different investment formulas, but the simplest uses equal parts of silica flour (around 200 mesh), pottery plaster, and water. These ingredients can be weighed out prior to mixing, or (if such precision goes against your nature) you can mix by feel, adding as you go.  With a bit of practice, you'll be able to estimate the correct amount of mixture you need to make.

It's best to finish the mold in one pouring, but if you mix too little you can let the mold set up and add more once it dries. Don't be discouraged if your first few attempts don't come out exactly right; with a little practice you'll soon become an expert.

It's not necessary to combine the two dry ingredients together before mixing, but there's no harm if you do. You should wear a respirator or approved mask when working with silica to keep from inhaling the potentially harmful silica dust.

Put the water in the mixing container. Use clean, room temperature tap water. Some people believe the results are better if you allow the water to sit for a few hours before using. 

Once you have the water in the container and the dry plaster and silica ingredients prepared, it's time to start the mixing process.

Click here to go to the next part of this series.


Copyright 2005 Brad Walker.  All rights reserved.

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