The present invention relates to a spray-polyurethane system which comprises a polyol component (A) and an isocyanate component (B), where the polyol component (A) comprises a1) at least one compound reactive with isocyanate, a2) at least one reactive chain extender having at least two groups reactive toward isocyanates, where at least one group reactive toward isocyanates is a free, primary NH2 group, and also a3) at least one metal catalyst, and a4) if appropriate, further additives, where the spray-polyurethane system comprises no amine catalyst. The present invention moreover relates to a process for production of a backing layer composed of polyurethane for moldings and to the use of this backing layer for production of automobile parts. Inventive backing layers have good mechanical properties, and low emissions, and their demolding time is small when compared with the open assembly time.