Non-cement fire door core

A method for making a fire door core from a wet mixture of materials, which method comprises:

• mixing water, expanded perlite, a binder component consisting essentially of calcined gypsum and an organic binder, and a fibrous reinforcement,
• wherein, on a water-free basis, the expanded perlite comprises about 70 to about 90 weight percent of the wet mixture, the calcined gypsum comprises about 10 to 15 weight percent of the wet mixture, the organic binder comprises about 1 to about 10 weight percent of the wet mixture and the fibrous reinforcement comprises about 0.2 to about 1 weight percent of the wet mixture, the water being present in an amount in excess of the stoichiometric amount needed to hydrate the calcined gypsum and sufficient to provide a damp mixture but less than an amount which would produce an aqueous slurry of the intermixed ingredients,
• placing a charge of the damp mixture in a pressure mold of slab form,
• applying sufficient pressure to the damp charge in the mold to compress the charge to about 25% to 33% of its original volume,
• maintaining the pressure until the compression strength of the compressed charge is at least about 50 psi,
• removing a molded slab from the pressure mold, and
• thereafter drying the slab by heating sufficiently to remove excess water,
• wherein the wet mixture contains less than 5 wt % of hydraulic cement.