The objective of this work is to show the effect of carbonation at early stages on fiber-cement composites and impact on hydration, chemical and dimension stability. Carbonation increased the content of CaCO3 polymorphs and consumed Ca(OH)(2) and other hydrated calcium phases. Micrographs and energy-dispersive spectrometry showed the CaCO3 formed is precipitated in the pore structure of the matrix, decreasing diffusion of Si, S, and Al during hydration. Therefore, a refining process of pore sizes is produced, and fiber-matrix interface in carbonated composites was improved, leading to volume stabilization of the composite, as indicated by lower drying shrinkage and lower porosity.