Gypsum Processing and Use
Practical Action
Once hardened, gypsum plaster is a hard and durable material, suitable for many building
applications. In a wet environment, however, it will soften irreversibly and eventually dissolve.
Portland cement or lime are often preferred as cements for outdoor use, as there is no easy
way to improve significantly the water resistance of gypsum.
Production processes
Gypsum processing plants vary widely in scale and level of technology. They range from plants
producing one or two tonnes per day using low-cost manual technologies, to plants of a
thousand tonnes per day that are highly mechanized and capable of producing different types
and grades of gypsum plaster or plaster boards.
There are five basic stages in gypsum processing:
Excavation is sometimes carried out by digging out an area of ground where the gypsum is
located using open-cast techniques. To reach deeper deposits drift or shaft mines may be
needed.
Crushing the gypsum rock is
advisable before processing further,
especially if subsequent heating is
to be done in a pan rather than a
shaft kiln. Crushing will ensure a
product which is more uniform and
requires less energy to heat.
Crushing can be done manually
with a hammer or hand-held roller,
but mechanical crushing is faster
and less laborious. Most clay-
crushing equipment, such as that
used for brick-making and pottery,
would be suitable. Crushing should
reduce the gypsum to grains of less
than a few millimetres across.
Gypsum sand does not need
crushing.
Screening with a sieve (manual or
motor-driven) will remove large
grains which have not been crushed
properly and which may contain
impurities.
Hopper
Output chute
with sieve
Safety
mesh
Pendulum
Figure 3: Crushing the gypsum ensures a more
uniform product which requires less energy to
heat. (This clay crusher was designed by J M Parry
Associates Ltd.)
Raw gypsum
Fuel Grinding, for example in a ball, rod, or
hammer mill, is necessary if the
gypsum is to be used for high quality
plasterwork or for moulding, medical,
or industrial applications. Unlike with
other cements, such as lime and
Ordinary Portland Cement, special
mills for mineral grinding may not be
required and the relatively soft gypsum
could be pulverised in agricultural
mills, which are generally widely
available.
Figure 4: A pit kiln is the simplest method of
heating gypsum, but it is inefficient compared
with other methods
Heating may be done in a number of
ways involving a range of technology
levels and costs. The simplest method
3