A method for calcining gypsum includes subjecting a composition including gypsum dihydrate to a predetermined vacuum. The method further includes maintaining the composition under the at least partial vacuum at a calcining temperature for a predetermined calcining time. The calcining temperature may be in a range from 60 C. to 125 C., or in a range from 65 C. to 85 C. The vacuum may be in a range from 25 mbar to 50 mbar. The predetermined calcining time may be in a range from 3 hours to 10 hours. The maintaining is effective to at least partially remove water of crystallization from the gypsum dihydrate to convert the composition to a product including gypsum hemihydrate.

Perlite-free, lightweight setting-type joint compounds which comprise calcium sulfate hemihydrate with a dry density of less than 50 lb/ft.sup.3, a foaming agent having a HLB value of at least 10 and preferably comprising an alkylbenzene sulfonic acid having a linear alkyl chain containing 8 to 14 carbons and/or a salt thereof, and a combination of rheology modifiers. Methods for building wallboard assemblies and methods for wall patch and repair projects that include applying the perlite-free, lightweight setting-type joint compounds to a substrate.

Perlite-free, lightweight setting-type joint compounds which comprise calcium sulfate hemihydrate with a dry density of less than 50 lb/ft.sup.3, a foaming agent having a HLB value of at least 10 and preferably comprising an alkylbenzene sulfonic acid having a linear alkyl chain containing 8 to 14 carbons and/or a salt thereof, and a combination of rheology modifiers. Methods for building wallboard assemblies and methods for wall patch and repair projects that include applying the perlite-free, lightweight setting-type joint compounds to a substrate.