Integrally waterproof fiber cement composite material

Integrally waterproof fiber cement composite materials including interior and exterior fiber cement articles for building structures are disclosed. Fiber cement formulations include small percentages of silica fume and silanol. Formulations may additionally include a cementitious binder, silica, and a density modifier such as calcium silicate or perlite. Advantageously, the addition of preselected small percentages of silica fume and silanol has been discovered to yield waterproofness at substantially lower concentrations of silica fume and silanol than would be required to yield waterproofness when using either silica fume or silanol alone.