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The chemistry of gypsum


Pure gypsum consists of hydrated calcium sulfate: CaSO4.2H20.

% of calcium in pure gypsum: 23.3%
% of sulfur in pure gypsum: 18.6%
% of oxygen (in sulfate) in pure gypsum: 37.2%
% of fixed water in pure gypsum: 20.9%
Premium Minimum 90% gypsum or 16.7% sulfur
Grade 1 Minimum 81% gypsum or 15.0% sulfur
Grade 2 Minimum 67% gypsum or 12.5% sulfur
Grade 3 Minimum 54% gypsum or 10.0% sulfur
Salt content NaCl less than 2%, (Na < 0.8%) otherwise warning required
Moisture The moisture content must be less than 15%
Fineness At least 50% of product must pass through a 2mm screen
At least 80% of product must pass through a 5.6mm screen
Heavy metals Should be less than 0.001% for cadmium
Should be less than 0.01% for lead

These standards essentially conform with those of Victoria and New South Wales. However these eastern States of Australia do not define a Premium Grade.


We have observed that some of our competitors are inconsistent in their bag labelling. Beware of bag labelling that claims 99% gypsum and Premium Grade when the sulfur analysis does not back this up. The ratio of gypsum content to sulfur content should be 5.38 to 1 and no higher.

The high purity and fine grain size of MENINGIE GYPSUM sets it apart from other gypsums, whether supplied in bags or bulk.