Patent ID: 7875114

Claim:
A method of reducing water in a gypsum slurry, comprising: preparing a gypsum slurry comprising water, calcined gypsum, a defoamer and a dispersant, wherein the dispersant consists essentially of a first and a second repeating unit, wherein said first repeating unit is an olefinic unsaturated mono-carboxylic acid repeating unit or an ester or salt thereof, or an olefinic unsaturated sulphuric acid repeating unit or a salt thereof, and said second repeating unit is of the general formula (I) where R 1 is represented by and wherein R 2 is hydrogen or an aliphatic C 1 to C 5 hydrocarbon group, R 3 is a non-substituted or substituted aryl group, and R 4 is hydrogen or an aliphatic C 1 to C 20 hydrocarbon group, a cycloaliphatic C 5 to C 8 hydrocarbon group, a substituted C 6 to C 14 aryl group or a group conforming to the formula wherein R 5 and R 7 , independently of each other, represent an alkyl, aryl, aralkyl or alkylaryl group and R 6 is a divalent alkyl, aryl, aralkyl or alkaryl group, p is 0, 1, 2, 3, inclusive, m and n are, independently, an integer from 2, 3, 4, 5, inclusive; x and y are, independently, integers from 1 to 350, inclusive and z is from 0 to 200, inclusive; adding a first portion of retarder to the slurry, the first portion being an amount of retarder sufficient to substantially prevent buildup of gypsum crystals within the mixer; adding a second portion of retarder to the slurry, the second portion being an amount of retarder sufficient to increase the fluidity of the slurry beyond that obtained by addition of the first portion of retarder.