The Abbey Church of Saint Mary and Saint Germain, Selby The Abbey’s magnesian limestone is prone to decay from salt efflorescence. In some areas the salts crystalise on the surface and seem to do little damage but in others, they crystalise under the surface, causing damage. Investigation in to the causes and effects has been on-going for over 10 years and have been taking place at the same time as others in the region, particularly at Howden Minster’s Chapter House where the Getty Institute and English Heritage are working more intensively. At the Abbey, study has included: investigation of the water table, possible leaks in the under-floor heating system, historic stone treatments (Nubindex), analysis of the types of salts found and mapping. We are continuing to monitor, after extensive external repair to the Choir to see whether this has an impact internally.