Plastic Coated Composite Building Boards and Method of Making Same

A method of manufacture for making a composite, multi-layered building panel comprising:

• providing non-woven, randomly aligned inorganic fibers;
• forming upper and lower mats by applying a binder to bind the randomly aligned inorganic fibers to each other, the upper and lower mats being porous and having interior and exterior surfaces defined by their orientation in the building panel;
• coating the upper and lower mats by applying upper and lower dense slurry layers so that the exterior surface of each mat is substantially covered by dense slurry and thereby forming a slurry boundary layer defined by the dense slurry covering the exterior surface of each mat, the boundary layer having a thickness of between approximately 0.01 to 2.0 mm, the upper and lower dense slurry layers including a polymeric additive entrained therein that increases the strength of the composite building panel;
• delivering a core slurry layer, having a density less than the density of the upper and lower dense slurry layers, onto the lower mat and dense slurry layer in an amount to provide for a predetermined thickness of the core slurry layer;
• applying the upper mat, including the dense slurry layer and the entrained additive, onto the core slurry layer, whereby the core slurry layer extends between and is bonded to the upper and lower dense layers;
• forming the surfaces of the upper and lower mats to produce the building panel having a predetermined thickness so that the slurry boundary layers are each disposed on an exterior surface of the mats;
• before the gypsum of the building panel completely sets, uniformly applying onto the slurry boundary layer of at least one of the upper and lower mat and dense slurry combinations a non-curing hot melt thermoplastic coating in a molten state at a temperature of between approximately 100° to 500° F. to a thickness of between 0.01 to 500 mils, the non-curing hot melt thermoplastic coating mechanically adhering to the at least one slurry boundary layer upon cooling, the thermoplastic coating cross-linking with the polymeric additive of the at least one upper and lower slurry layers to thereby form a composite polymer matrix.