Despite recent insights into thermal stability of ettringite and structural changes during decomposition, a lack of knowledge on nucleation and growth mechanisms of metaettringite remained. Therefore, a better understanding of the kinetic modelling of this heterogeneous reaction was proposed. Thanks to an experimental approach allowing to check the validity of kinetic assumptions (rate-determining step, expression of the rate as d alpha/dt=k f(alpha)...), a good agreement was found between the calculated and experimental alpha vs. t and d alpha/dt vs. t kinetic curves. The reaction area of the region in which the rate-limiting step occurs was also elucidated. Finally, we demonstrated that the rate-limiting step of the growth process follows an Arrhenius law in non-isothermal conditions.