Plasters of Calcined Gypsum or Calcium Sulfate

The distinction is thermal processing: raw gypsum and anhydrite (2520100000) are natural minerals in their geological state. Plasters under 2520200000 have been calcined — heated to partially or fully dehydrate the calcium sulfate — making them reactive binders that set when mixed with water. The presence of calcination, confirmed by a certificate of analysis showing loss on ignition or hemihydrate content, is the classification trigger.

While calcined gypsum plasters are not subject to mandatory admissibility review by a specific regulatory agency for general construction use, importers should ensure commercial invoices clearly state the product's chemical form (hemihydrate or anhydrite), intended end use, and country of origin. Products marketed for dental or medical casting applications may attract additional scrutiny from FDA. A licensed customs broker can advise on any applicable marking requirements.