A curable casting compound, including a polymeric binder and at least one particulate filler incorporated therein, wherein the filler is ground fruit kernels and/or fruit shells, wherein either only the at least one filler composed of ground fruit kernels and/or fruit shells or additionally at least one further particulate inorganic filler is present.

A composite lumber comprising a curable polymer and renewable natural materials, from a plant-based and/or tree-based source, as well as a method for manufacturing the same. In a preferred embodiment, the composite lumber is cast to a specific size and shape, for example as commonly utilized in commercial or home building industries. The composite lumber includes different sizes of natural materials which impart desirable properties thereto. In one embodiment, the method of the invention incorporates the different-sized natural materials in a sequential order based on size, starting from the smallest size.