are to be avoided or minimized the dihydrate may contain considerable amounts of anhydrite sand or clay and the like without significant impairment of accelerator activity the feed material may be preground as needed to a feed size that will result in average particle size of a minimum of about 7000 square centimeters per gram blaine after treatment in accordance with the present invention the first coating material may be any of those conventional calcination inhibiting materials well known in the art for example but without limitation various sugars glycerine glycols starches anionic or nonionic detergents lignin or lignosulfonates and mixtures thereof may be used with or without the further addition of boric acid for reasons of economy effectiveness and availability sugar is the preferred first coating material the sugar may be sucrose dextrose or amylose but sucrose is generally preferred for reasons of availability and economy the calcination inhibiting agent such as sugar will constitute about 5 15 by weight of the calcium sulfate dihydrate when the dihydrate employed contains considerable relatively inert extender material such as sand or calcium sulfate anhydrite the percentage of calcination inhibiting agent based on the weight of the dihydrate present may be much larger.