Abstract: A composite building article is configured with one or more subsurface interfacial zones provided to improve the durability of the article. Each subsurface interfacial zone is made of a matrix of fiber cement and radiation curable material. The radiation curable material forms an interlocking network with the fiber cement to provide a interfacial zone against ingress of environmental agents that can degrade the article. The number, configuration and distribution of the subsurface interfacial zones can vary dependent on the desired characteristics of the final product. The subsurface interfacial zones also improves the adhesion between exterior coatings and the substrate as the interfacial zones can be integrally formed with the substrate as well as exterior coating layer.