Abstract: The invention relates to compositions intended to be applied to surfaces of freshly poured mortar and/or concrete mixes, before the start of setting, in order to prevent the evaporation of water needed for them to set and harden, which are distinguished by the fact that, for the purpose of making them synergistic with regard to water retention, they are composed, in the form of aqueous emulsions, of: a) at least one petroleum-derived or synthetic paraffin wax containing, as a mixture, saturated and unsaturated aliphatic hydrocarbons of general formulae CnH2n+2 and CnH2n for which n is at least equal to 30 and the melting point of which is between 40° C. and 75° C.

Abstract: The invention concerns the use of a selected polycarboxylic type dispersant for aqueous calcium sulfate hemihydrate compositions that, simultaneously with its dispersing action, can control the initial setting and/or final setting times for said compositions. The invention also concerns aqueous calcium sulfate hemihydrate compositions comprising said dispersant or a mixture of said dispersants.