Atomistic-scale computer simulations, based on the ionic model, have been used to study intrinsic defect processes in a range of Ca-Al-Fe-O cement-phase compounds. The simulations accurately reproduce the structures of this diverse set of materials and predict the large disorder observed between the aluminium and iron sublattices in C(4)AF. Additionally, the calculations predict that the extent of intrinsic disorder varies considerably from material to material, as does the dominant mode of disorder. Finally, the calculations indicate that clustering of defects is likely to play an important role in the mass transport mechanisms of all the compounds studied.