The proposal presented here is to use accelerated carbonation via carbonated water to modify the microstructure of the cementitious matrix. Carbonated water was tested in different conditions of molding and curing of the fiber-cement composites. This particular carbonation process generates stabilization of the pore volume of the composite and reduced the degradation of the cellulosic fibers by the consumption of CH and formation of the CaCO3 in early age. The results indicated that carbonated water was suitable for improving hydration, and as a carbonating agent in the fiber-cement composites. The curing carbonation yielded substantial mechanical and physical gains, as well as further protection of the cellulosic fibers against mineralization into the cement.