A process for preparing hydrophobized concrete or mortar comprising the steps of providing a cement slurry suitable for concrete or mortar preparation; adding an aqueous alkyl ketene dimer dispersion comprising (a) an alkylketene dimer of the formula and/or of the formula in which R 1 and R 2 are identical or different hydrocarbon radicals comprising 10 to 24 carbon atoms, or an alkyl ketene dimer in solid form; (b) at least one emulsifier having a nitrogen content of ≤ 1 % by weight selected from the group consisting of a starch, cellulose, starch derivative or cellulose derivative; (c) a condensation product of phenol sulfonic acid and formaldehyde, naphthalene sulfonic acid and formaldehyde or naphthalene sulfonic acid, phenol, formaldehyde and urea wherein the sulfonic acid groups may optionally be present in protonated or deprotonated or partly in protonated and partly in deprotonated form; wherein the dispersion has a charge density in the range from -5 to -150 μeq/g and wherein the charge density of the dispersion is determined with a coulometer at pH 3,5 with a 0.001 moL/L Poly-DADMAC-solution for anionic surfaces and 0.001 mol/L Sodium polyethylene sulfonate for cationically charged particle surfaces and wherein the condensation product (c) is present in an amount of 0.1 to 5 wt% based on said condensation product; and allowing the cement slurry to harden or allowing the cement slurry of step to harden and applying said aqueous alkyl ketene dispersion as defined above to the surface of the hardened cement. providing a cement slurry suitable for concrete or mortar preparation; adding an aqueous alkyl ketene dimer dispersion comprising (a) an alkylketene dimer of the formula and/or of the formula in which R 1 and R 2 are identical or different hydrocarbon radicals comprising 10 to 24 carbon atoms, or an alkyl ketene dimer in solid form; (b) at least one emulsifier having a nitrogen content of ≤ 1 % by weight selected from the group consisting of a starch, cellulose, starch derivative or cellulose derivative; (c) a condensation product of phenol sulfonic acid and formaldehyde, naphthalene sulfonic acid and formaldehyde or naphthalene sulfonic acid, phenol, formaldehyde and urea wherein the sulfonic acid groups may optionally be present in protonated or deprotonated or partly in protonated and partly in deprotonated form; wherein the dispersion has a charge density in the range from -5 to -150 μeq/g and wherein the charge density of the dispersion is determined with a coulometer at pH 3,5 with a 0.001 moL/L Poly-DADMAC-solution for anionic surfaces and 0.001 mol/L Sodium polyethylene sulfonate for cationically charged particle surfaces and wherein the condensation product (c) is present in an amount of 0.1 to 5 wt% based on said condensation product; and allowing the cement slurry to harden or allowing the cement slurry of step to harden and applying said aqueous alkyl ketene dispersion as defined above to the surface of the hardened cement. adding an aqueous alkyl ketene dimer dispersion comprising (a) an alkylketene dimer of the formula and/or of the formula in which R 1 and R 2 are identical or different hydrocarbon radicals comprising 10 to 24 carbon atoms, or an alkyl ketene dimer in solid form; (b) at least one emulsifier having a nitrogen content of ≤ 1 % by weight selected from the group consisting of a starch, cellulose, starch derivative or cellulose derivative; (c) a condensation product of phenol sulfonic acid and formaldehyde, naphthalene sulfonic acid and formaldehyde or naphthalene sulfonic acid, phenol, formaldehyde and urea wherein the sulfonic acid groups may optionally be present in protonated or deprotonated or partly in protonated and partly in deprotonated form; wherein the dispersion has a charge density in the range from -5 to -150 μeq/g and wherein the charge density of the dispersion is determined with a coulometer at pH 3,5 with a 0.001 moL/L Poly-DADMAC-solution for anionic surfaces and 0.001 mol/L Sodium polyethylene sulfonate for cationically charged particle surfaces and wherein the condensation product (c) is present in an amount of 0.1 to 5 wt% based on said condensation product; and allowing the cement slurry to harden or (a) an alkylketene dimer of the formula and/or of the formula in which R 1 and R 2 are identical or different hydrocarbon radicals comprising 10 to 24 carbon atoms, or an alkyl ketene dimer in solid form; (b) at least one emulsifier having a nitrogen content of ≤ 1 % by weight selected from the group consisting of a starch, cellulose, starch derivative or cellulose derivative; (c) a condensation product of phenol sulfonic acid and formaldehyde, naphthalene sulfonic acid and formaldehyde or naphthalene sulfonic acid, phenol, formaldehyde and urea wherein the sulfonic acid groups may optionally be present in protonated or deprotonated or partly in protonated and partly in deprotonated form; wherein the dispersion has a charge density in the range from -5 to -150 μeq/g and wherein the charge density of the dispersion is determined with a coulometer at pH 3,5 with a 0.001 moL/L Poly-DADMAC-solution for anionic surfaces and 0.001 mol/L Sodium polyethylene sulfonate for cationically charged particle surfaces and wherein the condensation product (c) is present in an amount of 0.1 to 5 wt% based on said condensation product; and allowing the cement slurry to harden or allowing the cement slurry of step to harden and applying said aqueous alkyl ketene dispersion as defined above to the surface of the hardened cement.