Highly-filled polyurethane composites with fiber reinforcement

A method of manufacturing a composite panel comprising:

• mixing (i) one or more isocyanates selected from the group consisting of diisocyanates, polyisocyanates, and mixtures thereof, (ii) one or more polyols, and (iii) from 40% to 90% by weight, based on the total weight of a polyurethane composite, of a particulate filler to form a mixture;
• allowing the one or more isocyanates and the one or more polyols to react in the presence of the particulate filler to form a polyurethane composite having a first surface and a second surface opposite the first surface;
• applying a first fiber reinforcement to the first surface of the polyurethane composite, wherein the first fiber reinforcement comprises a glass fiber having a basis weight of from 0.5 g/ft2 to 10 g/ft2;
• applying a cementitious slurry comprising a cement to the first fiber reinforcement;
• and
• allowing the cementitious slurry to cure to form the composite panel,
• wherein the cementitious layer provides a wettable bonding surface to the composite panel, and the polyurethane composite is a barrier to water absorbed by the cementitious layer that prevents water from passing through the polyurethane composite.