Abstract: A set accelerator for at least one of accelerating the hydration rate and reducing the set time of an aqueous slurry of calcium sulfate hemihydrate is described. The set accelerator consists of a mixture of ground calcium sulfate dihydrate and zinc sulfate material. Aluminum sulfate material is an optional component of the set accelerator. The set accelerator is particularly useful in accelerating the hydration rates of sprayable plasters. A fluid form of the set accelerator may be made by suspending the solids in water. The fluid form is advantageously used in ready mixed setting type joint compounds.

Abstract: A two part joint compound which sets by hydration of calcium sulfate hemihydrate to gypsum and is clay-free. One part includes an in-situ acidic acrylate copolymer thickener (i.e., an associative thickener) with the calcium sulfate hemihydrate, along with a non-calcium bearing phosphate set preventer. The first part contains water, but remains unset for at least 175 days. The second part includes a set initiator compound having a cation with a log K value greater than calcium ions. The second part is mixed with the first part when setting is desired.

Abstract: The present invention relates to a method for minimizing the buildup of set gypsum on a tool used to apply a calcium sulfate hemihydrate-containing composition to a surface as well as to a method for cleaning a tool having set gypsum deposited thereon. The method for cleaning a tool having set gypsum deposited thereon comprises the steps of (a) contacting the tool with a cleaning solution having a pH of less than about 7, said cleaning solution which comprises a non-calcium phosphate, water, and, optionally, a pH modifier; (b) optionally agitating the solution; (c) removing the tool from the cleaning solution; and (d) rinsing the tool with water. The method for minimizing the buildup of set gypsum on a tool further comprises step (e) using the tool to apply a calcium sulfate hemihydrate-containing composition. An additional step (f), flushing the tool with water, may also be employed.

Abstract: A cementitious composition of the setting type which can be kept in a ready-mixed state and which can be caused to set and harden upon introduction of an accelerator with reproducibility and set time predictability. The cementitious base composition contains calcium sulfate hemihydrate as a principal filler material and certain non-calcium bearing phosphate additives which prevent setting action in the presence of water. An accelerator, such as zinc sulfate, may be added to the ready-mixed, cementitious composition to initiate the setting action, or the ready-mixed cementitious composition can be used as a drying type joint compound without the addition of an accelerator.

Abstract: A clay-free, asbestos-free and glass microbubble-free, drying type Joint compound containing an in-situ or associative thickener as a substitute for asbestos and any clay substitute therefor. In particular, these drying type joint compounds contain no attapulgus clay thereby improving viscosity stability, crack resistance and shrinkage. The lightweight joint compounds contain treated expanded perlite, treated to render it water-insensitive. The preferred in-situ thickeners are acidic acrylate copolymers. It has been found that the in-situ thickeners should be used in combination with the normal cellulosic thickeners used in joint compounds Instead of as replacements therefor. The joint compounds contain the usual fillers and latex emulsion binders, with at least about 50% by weight of the drying type joint compound being a filler selected from the group consisting of calcium carbonate and calcium sulfate dihydrate.