A composite product includes gypsum in an amount of 60 to 90% by weight, fibers in an amount of 1.5 to 26% by weight substantially homogeneously distributed through the composite, and a rheology-modifying agent in an amount of 0.5 to 6% by weight. The composite is caused or allowed to cure to form a cured composite. The cured composite is a fire resistant component used in a fire-rated door core, a fire-rated door or a fire-rated building panel. The fire resistant component may include a building panel, a door panel, a door core, a door rail, a door stile, a door lock block, a door border, or a door insert.