Disclosed are a composite gypsum board and a method of preparing gypsum board. The board contains at least one set gypsum layer sandwiched between face and back cover sheets. The set gypsum layer is formed from at least stucco and water. The stucco material generally includes a high salt impurity content, for example, when the stucco is calcined from certain sources of low-quality synthetic gypsum. For example, in some embodiments, the salts are chloride salts, e.g., sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl2), and/or calcium chloride (CaCl2). The board and methods improve the bond between the gypsum layer(s) and at least one of the cover sheets (e.g., the back cover sheet). Also provided are methods and systems relating to drying gypsum board.