I would be careful buying Gypsum that's not food grade
Quote
Gypsum. This is an imperative in clay soils, making clay particles cleave together improving friability and drainage. But there's gypsum, and there's gypsum. Geologist Sean Kennedy enlightens us. "Gypsum is a natural product that forms in different geological environments such as dunes or lake beds", and therefore can contain impurities such as sand or clay. It is the ratio of sulphur to gypsum which is important, 94% gypsum to 17.5% sulphur is ideal. The other important aspect is the grain size of the gypsum. The finer it is the more quickly it is effective. It's colour is also an indication of its purity. Gypsum is very pale and more colouration is an indication of impurities. There are standards for gypsum. South Australia recognised 4 grades. Anything below 54% gypsum or 4% sulphur does not count as gypsum. Malcolm looks at three different brands of 'premium grade' gypsum and discovers that two don't live up to their labels.
Batz