Plaster/Silica Mixtures for Mold Making
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
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
Click here to go to the
next part of this series.
Copyright 2005 Brad Walker.
All rights reserved.