Since its invention in 1908, calcium aluminate cement (CAC) has been used as a full binder to formulate materials in a wide range of niches applications like monolithic refractories, rapid concrete, corrosion resistance lining etc....CAC has also been used in the last three decades as a compound of formulated binders combining CAC, Portland cement (OPC) and calcium sulfate (C$Hx) leading to the formation of ettringite.The development of this hydrate can lead to various properties like rapid setting and hardening, rapid drying or shrinkage compensation.Thanks to this technology, special construction mortars have been successfully developed over the years, for example self-leveling compounds with time to service as rapid as a few hours.In this context CAC can be seen as key precursor for the reaction leading to ettringite.This paper gives an overview of the different hydration reactions involved in ettringite formation and the link with applicative properties.It is shown that depending on the binder composition (relative % of CAC, OPC, C$Hx) or the raw material selection (for example C$Hx type), the hydration path and the subsequent microstructure can be very different with an important impact on properties.