Joint compounds, activators and methods for setting a joint compound and preventing seed setting

A method for inhibiting formation of gypsum seeds in a ready-mixed setting type joint compound, the method comprising:

• mixing at least calcined gypsum, water, at least one non-calcium phosphate compound and at least one metal ion control agent comprising an aminopolycarboxylic acid and/or a salt thereof, and thereby obtaining a ready-mixed setting joint compound,
• wherein the metal ion control agent is used in an amount from about 0.01% to about 10% by weight of calcined gypsum;
• and
• wherein the metal ion control agent inhibits formation of gypsum seeds in the ready-mixed setting type joint compound during storage;
• and
• wherein the method further comprises blending together a first activator and a second activator, and thereby obtaining a set activator blend;
• and
• mixing the set activator blend with the ready-mixed setting type joint compound;
• and
• wherein the first set activator is zinc oxide, zinc hydroxide and/or zinc salt and wherein the second set activator is aluminum oxide, aluminum hydroxide and/or aluminum salt;
• wherein the ratio of the first set activator to the second set activator in the set activator blend is in the range from 3:1 to 1:1 by dry weight of the first set activator to the second set activator, and the mixing of the set activator blend with the ready-mixed setting type joint compound is performed at a temperature in the range from 40° F. to 65° F., and wherein the set activator blend is added in an amount from 0.5% to 5% by weight to the setting joint compound, excluding water.