Staining on heritage building stone identified by NMR spectroscopy

Brown staining on both pristine and painted sandstone surfaces is a regular problem reported from new building construction and restoration actions. During the recent restoration of the Großer Wendelstein, an impressive airy stone staircase in the castle Hartenfels in Torgau, Germany, extensive brown staining appeared in distinctive places. Due to the fact that such an incidence occurred while desalination with poultice compresses the usually extreme rare chance of sampling was possible and executed. Several chemical tests combined with Nuclear Magnetic Resonance (NMR) and Infrared (IR) spectroscopy proved humic substances as causation of the intensive staining. In the consequence restorative recommendations are drawn.