Additive for hydraulically setting compositions

An additive for hydraulically setting compositions, comprising a colloidally disperse preparation comprising

• a) at least one salt of at least one polyvalent metal cation with at least one organic phosphonate and/or organic phosphate compound as anion, optionally in a mixture with at least one compound capable of releasing an inorganic anion selected from carbonate, oxalate, silicate, phosphate, polyphosphate, phosphite, borate, aluminate and sulphate, which forms a sparingly soluble salt with the polyvalent metal cation and
• b) at least one polymeric dispersant comprising anionic and/or anionogenic groups and polyether side chains,
• wherein the polyvalent metal cation selected from Al3+, Fe3+, Fe2+, Zn2+, Mn2+,Cu2+, Mg2+, Ca2+, Sr2+, Ba2+ and mixtures thereof, and wherein the metal cation is present in an amount corresponding to the following formula (a):
• 0.1
• <
• Σ
• i
• 
• z
• K
• ,
• i
• *
• n
• K
• ,
• i
• Σ
• j
• 
• z
• S
• ,
• j
• *
• n
• S
• ,
• j
• <
• 50.
• (
• a
• )
• where
• zK,i is the magnitude of the charge of the polyvalent metal cation,
• nK,i is the number of moles of the polyvalent metal cation weighed in,
• zS,j is the magnitude of the charge of the anionic and anionogenic group present in the polymeric dispersant,
• nS,j is the number of moles of the anionic and anionogenic group present in the polymeric dispersant weighed in,
• the indices i and j are independent of one another and are an integer greater than 0, where i is the number of different kinds of polyvalent metal cations and j is the number of different kinds of anionic and anionogenic groups present in the polymeric dispersant.