Wallboards are produced by methods which use significantly reduced Embodied Energy when compared with the energy used to fabricate gypsum wallboard. A novel binder, consisting in one embodiment of monopotassium phosphate and magnesium oxide, and combined with various fillers, is used to provide a controlled exothermic reaction to create a gypsum board-like core which can be wrapped in a selected material such as recycled paper and manufactured on a conveyor system to appear and handle like gypsum wallboard, but without the large energy required to make gypsum wallboard. The resultant product may be used in interior or exterior applications and possesses the fire, sound and other important properties of gypsum wallboard. As energy costs increase, the novel wallboards of this invention can become less expensive to manufacture than traditional wallboard. The manufacturing process results in much lower greenhouse gas emissions than the processes used to make gypsum wallboard.