Additive for hydraulically setting compositions

An additive for hydraulically setting compositions, comprising a colloidally disperse preparation of at least one salt of a mono- or polyvalent metal cation, at least one compound which is able to release an anion which forms a low-solubility salt with the metal cation, and a dispersant comprising 70 to 100% by weight of the total dispersant of a polymeric sulfonated dispersant having anionic and/or anionogenic groups which is selected from sulfonated ketone-formaldehyde condensates, sulfonated melaminesulfonate-formaldehyde condensates, naphthalenesulfonate-formaldehyde condensates, lignosulfonates and sulfonated copolymers obtained by radical copolymerization and

• where the metal cation is selected from Ca2+, Al3+, Fe3+, Fe2+, Zn2+, Mn2+, Cu2+, Mg2+, Sr2+, Ba2+, Li+, and mixtures thereof, and where the metal cation is present in a quantity such that the following condition (a) is met:
• 0.1
• <
• ∑
• i
• ⁢
• z
• K
• ,
• i
• *
• n
• K
• ,
• i
• ∑
• j
• ⁢
• z
• S
• ,
• j
• *
• n
• S
• ,
• j
• <
• 30
• (
• a
• )
• where
• zK,i is the amount of the charge number of the metal cation,
• nK,i is the number of mols of the weighed-in metal cation,
• zS,j is the amount of the charge number of the anionic and anionogenic groups present in the polymeric dispersant,
• nS,j is the number of mols of the anionic and anionogenic groups present in the weighed-in polymeric sulfonated dispersant,
• 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 metal cations and j is the number of different kinds of anionic and anionogenic groups present in the polymeric dispersant.