Composite panel-board and method of making same

A method of fabricating a composite panel board which is made up of a rigid, gypsum board base panel having a rigid, organic plastic, foam layer and substantially covering one of the broad, flat surfaces of said gypsum board base panel, with the foam layer being formed in-situ on and self-adherant to said one of the broad, flat surfaces of said gypsum board, said method comprising attaching edge sheets on or adjacent to the mutually opposite side edges of said base panel;

• maintaining the edge sheets in a position extending upwardly from the base panel so that the mutually opposite edge sheets together with said base panel form a trough;
• heating the upper surface of the base panel to a temperature of at least about 95.degree. F. in the presence of a water unsaturated atmosphere, thereby removing moisture from the upper surface layer of the gypsum board base panel;
• applying a uniform layer of a foamable, liquid, organic plastic material on the upper surface of the base panel, said plastic material being capable of, within a relatively short time period following its being applied on the base panel as a liquid, expanding and forming itself into a layer of rigid, organic plastic foam in-situ on the surface of the base panel;
• applying a sheet of water-vapor-resistant, flame-retardant material to the exposed surface of the layer of liquid, organic plastic material before the plastic material has had time to expand and form said layer of rigid, organic plastic foam;
• and allowing the liquid, organic plastic material to expand and form a layer of rigid foam adhered on its underside to the gypsum board base panel and on its upperside to the sheet of water-vapor-resistant, flame-retardant material.