A composition comprising a carbodiimide and a polymer, wherein the carbodiimide comprises a reaction product of a) at least one of an aliphatic C4 to C20 polyisocyanate and an araliphatic C4 to C20 polyisocyanate, b) at least one of a hydroxy carboxylic acid and a hydroxy carboxylic salt, c) optionally, a further compound carrying groups able to react with isocyanate groups in an addition reaction, d) optionally, at least one other isocyanate, and the carbodiimide units being derived essentially exclusively from the isocyanate groups of component a), and the polymer comprises a reaction product of an ethylenically unsaturated carboxylic acid and at least one of a (meth)acrylate, a vinyl ester of a carboxylic acid, a vinyl aromatic compound, an ethylenically unsaturated nitrile, a vinyl halide, an aliphatic hydrocarbon, and a free-radically polymerizable monomer. Also, a method of applying the composition on and/or in a substrate.