A ready-mixed setting type joint compound in which formation of gypsum seeds has been inhibited. A method for controlling a setting reaction by mixing a ready-mixed setting type joint compound with one or more metal ion control agents comprising aminopolycarboxylic acid and/or a salt thereof, and further mixing the setting type joint compound with one or more non-calcium phosphate compounds. The method may further comprise mixing the setting type joint compound with a set activator obtained by blending together a first set activator including a cadmium compound, lead compound and/or zinc compound and a second set activator including a ferrous compound, aluminum compound and/or manganese compound.