Disclosed are a gypsum board, and related slurries and methods. The gypsum board comprises a gypsum layer disposed between two cover sheets. The gypsum layer comprises a crystalline matrix of set gypsum and expandable graphite. The expandable graphite exhibits volume expansion at high temperatures. Optionally, unexpanded vermiculite can also be included in the gypsum layer to provide an expansion component at even higher temperatures. Because of synergy between the expandable graphite and unexpanded vermiculite in accordance with some embodiments, less vermiculite can be included in the board than in conventional board that contained vermiculite. The board desirably can pass one or more fire-related tests, and is a fire-rated board in some embodiments.