The present invention relates to a process for preparing polyurethanes by mixing a) polyisocyanate, b) a mixture obtainable by introducing an alkali metal or alkaline earth metal salt into a compound comprising urethane groups, c) compounds comprising one or more epoxide groups, and, optionally, d) polyol, e) chain extenders, and f) fillers and further additives to form a reaction mixture and fully reacting the mixture to give the polyurethane, where the amount of alkali metal or alkaline earth metal ions per equivalent urethane groups in the compound (b) is 0.0001 to 3.5. The present invention further relates to a polyurethane obtainable by such a process, and to the use of such a polyurethane for producing bodywork components for vehicles.