Most foreign plastering gypsum is made by mixing half-water gypsum with anhydrous gypsum, adding water-retaining agents and other additives, as well as other aggregates.

When mixing plaster, variations in raw gypsum, firing conditions, fineness, and water-to-plaster ratios can all impact product stability. Stability of plastering plaster products is currently the primary issue in the plastering plaster industry.

Achieving a stable performance in our building gypsum is crucial. This is because the calcination process often results in multiphase mixtures, which greatly affect the setting time of the gypsum.

In practical production, if the retardant fails to properly adjust the setting time (at times, no matter how much retardant is added, the setting time of gypsum cannot be extended to the required duration), it is essential to first check for an excessive amount of Type III anhydrite or underburnt dihydrate phases in the building gypsum powder.

Type III anhydrite, also known as dehydrated hemihydrate, is an unstable phase that inevitably exists during the production of hemihydrate. However, it can be converted into hemihydrate through aging processes. Neglecting this can lead to inconsistent performance in the preparation of plastering gypsum using hemihydrate, mainly manifested as varying setting times for each batch of plastering gypsum when the same amount of retardant is used. The reason lies in the role of Type III anhydrite in the hemihydrate during the gypsum hydration process, where the proportion of Type III anhydrite affects the retarding effect. This is the primary reason many production enterprises fail to achieve stable performance in their plastering gypsum formulations using hemihydrate.