Liquid curing agent for curing polymer resins, in particular epoxy resins, comprising: a) cyanamide and b) at least one urea derivative of formula or formula wherein the following, in each case simultaneously or independently of one another, apply to the residues and at least one residue R 1, R 2, R 3 is not hydrogen: R 1, R 2, simultaneously or independently of one another, are hydrogen, C1 to C15 alkyl, C3 to C15 cycloalkyl or, together to form a ring, C3 to C10 alkylene; R 3 is hydrogen, C1 to C15 alkyl, C3 to C15 cycloalkyl, aryl, aryl alkyl, C1 to C15 alkyl substituted with -NHC NR 1 R 2, C3 to C15 cycloalkyl substituted with -NHC NR 1 R 2, aryl substituted with -NHC NR 1 R 2 or aryl alkyl substituted with -NHC NR 1 R 2; R 4, R 5, R 6, R 7, R 8, simultaneously or independently of one another, are hydrogen, halogen, C1 to C15 alkyl, C3 to C15 cycloalkyl, aryl, aryl alkyl, -CF 3, -NHC NR 1 R 2, C1 to C15 alkyl substituted with -NHC NR 1 R 2, aryl substituted with -NHC NR 1 R 2 or aryl alkyl substituted with -NHC NR 1 R 2, characterised in that the liquid curing agent comprises cyanamide and at least one urea derivative of formula or formula in a cyanamide: urea derivative molar ratio of 1:1 to 4:1. a) cyanamide and b) at least one urea derivative of formula or formula wherein the following, in each case simultaneously or independently of one another, apply to the residues and at least one residue R 1, R 2, R 3 is not hydrogen: R 1, R 2, simultaneously or independently of one another, are hydrogen, C1 to C15 alkyl, C3 to C15 cycloalkyl or, together to form a ring, C3 to C10 alkylene; R 3 is hydrogen, C1 to C15 alkyl, C3 to C15 cycloalkyl, aryl, aryl alkyl, C1 to C15 alkyl substituted with -NHC NR 1 R 2, C3 to C15 cycloalkyl substituted with -NHC NR 1 R 2, aryl substituted with -NHC NR 1 R 2 or aryl alkyl substituted with -NHC NR 1 R 2; R 4, R 5, R 6, R 7, R 8, simultaneously or independently of one another, are hydrogen, halogen, C1 to C15 alkyl, C3 to C15 cycloalkyl, aryl, aryl alkyl, -CF 3, -NHC NR 1 R 2, C1 to C15 alkyl substituted with -NHC NR 1 R 2, aryl substituted with -NHC NR 1 R 2 or aryl alkyl substituted with -NHC NR 1 R 2, characterised in that the liquid curing agent comprises cyanamide and at least one urea derivative of formula or formula in a cyanamide: urea derivative molar ratio of 1:1 to 4:1. R 1, R 2, simultaneously or independently of one another, are hydrogen, C1 to C15 alkyl, C3 to C15 cycloalkyl or, together to form a ring, C3 to C10 alkylene; R 3 is hydrogen, C1 to C15 alkyl, C3 to C15 cycloalkyl, aryl, aryl alkyl, C1 to C15 alkyl substituted with -NHC NR 1 R 2, C3 to C15 cycloalkyl substituted with -NHC NR 1 R 2, aryl substituted with -NHC NR 1 R 2 or aryl alkyl substituted with -NHC NR 1 R 2; R 4, R 5, R 6, R 7, R 8, simultaneously or independently of one another, are hydrogen, halogen, C1 to C15 alkyl, C3 to C15 cycloalkyl, aryl, aryl alkyl, -CF 3, -NHC NR 1 R 2, C1 to C15 alkyl substituted with -NHC NR 1 R 2, aryl substituted with -NHC NR 1 R 2 or aryl alkyl substituted with -NHC NR 1 R 2, characterised in that the liquid curing agent comprises cyanamide and at least one urea derivative of formula or formula in a cyanamide: urea derivative molar ratio of 1:1 to 4:1.