Drying plaster/silica molds
Click here for basic
information on plaster/silica molds for casting and slumping.
Although it's usually recommended that plaster/silica molds be
air dried before firing in the kiln, that process can take several
days. With larger molds (or humid environments) it's not
unusual for it to take a week or more to thoroughly air dry the
For those who can't wait, there are several ways to speed up
this process. While these methods may be more risky than
waiting for the kiln to air dry, they do save time. And if
done properly, they can be just as successful as traditional air
The first method is simply to kiln dry the mold, using a slow
firing schedule the allows for soaks at appropriate places to ensure
that all moisture is driven from the mold. This technique
sometimes results in small cracks in the mold (especially if the
walls of the mold are thick), but the mold is usually serviceable
for firing and casting.
A second approach is to fill the mold with glass and then fire
slowly in order to give the mold time to dry as the temperature
increases. This avoids the need for a separate firing to dry
the mold and also makes it possible to fire plaster/silica molds
fairly quickly after they have been poured.
A third technique, which takes more time but is still quicker
than air drying, is especially appropriate for larger or thicker
molds that don't perform as well when fired in the kiln while wet.
This involves the construction of a drying box to speed up the
drying process. The drying box is inexpensive and fairly easy
All three of these techniques will be discussed
in greater detail in future tips.
Copyright 2005 Brad Walker.
All rights reserved.