The invention describes a phosphate-based inorganic binder obtained by reaction between at least one basic constituent and an acidic phosphate salt, in the presence of a retarder which is an X+A− salt, the solubility of which in an aqueous medium, measured at 25° C., is greater than that of the acidic phosphate salt, and in which: X+ is a cation chosen from alkali metals, alkaline earth metals, zinc, aluminium and the ammonium ion, and A− is an acetate, formate, benzoate, tartrate, oleate, oxalate, bromide or iodide anion.