For preparing gypsum board slurry contains a calcined gypsum, water, foaming agent and coalescing agent. Foaming agent imparts a large number of air bubbles in the slurry. Typically, a pre-generated foam as a blowing agent and using a foam by forming a slurry giving a large number of air bubbles in the foam slurry. The adhesion causes coalescence of a plurality of air bubbles granted by the foam. Typically, the adhesion creates a larger and more discrete bubbles by coalescence of a plurality of small air bubbles in the bonded part, granted by the foam. In addition, gypsum board and the method for forming the slurry, and gypsum board forming method may be served. The gypsum board comprises a gypsum layer formed from the slurry. Gypsum layer is given by the foam in the slurry, and the adhesion to limit the number of bubbles dispersed therein.