The invention relates to a method for repairing composite elements comprising the following structure: (i) 1 - 20 mm metal, (ii) 10 - 300 mm polyisocyanate polyaddition products obtainable by reacting (a) isocyanates (b) compounds which can react against isocyanates, (iii) 1 - 20 mm metal. According to the invention, a section containing (i), (ii) and optionally (iii) is cut from the composite element and removed from the cutting surfaces of the remaining composite element, so that (i) and optionally (iii) extend beyond (ii), when (iii) is removed, by (x) at least 7cms; the cut sections (i) and optionally (iii) are replaced by new layers (ia) and optionally (iiia), and connection occurs with the remaining layers (i) and optionally (iii) of the composite element. Finally, in the space between the layers (i)/(ia) and (iii), and optionally (iii)/(iiia) (a) isocyanates are reacted with (b) isocyanate reactive compounds.