Assertion: synthetic gypsum | /r/HasProperty | essential
Facets:
Source sentences:
text: It is, of course, possible to dry the synthetic gypsum and, if desired, to subject it to a preliminary grinding operation, before adding the carbonate, but it is essential that the carbonate be intimately blended with the gypsum before calcination begins.
text: It is also essential that the calcined material be milled after calcination, if a satisfactory plasterboard product is to be produced.