The invention relates to an ettringite binder for dense mortar, comprising calcium sulphates and a calcium aluminate mineral compound, the calcium aluminate mineral compound comprising calcium C and aluminum A oxides, soluble and combined in one or more crystallized and/or amorphous mineralogical phases, in such proportions that: the useful C/A molar ratio of the calcium aluminate mineral compound ranges from 1.2 to 2.7; the sum in weight of the useful (C+A) phases accounts for at least 30% of the total weight of the mineral compound.