Investigating the effects of humidity and salt crystallisation on medieval masonry

An investigation of the effects of humidity and salt crystallisation on medieval masonry has been undertaken at the parish church of Walpole St Andrew, Norfolk, with the intention of establishing a relationship between changes in environmental conditions and levels of stone decay. Masonry within the church has been contaminated with sodium chloride salts, which are undergoing cycles of crystallisation/dissolution in response to fluctuations in relative humidity corresponding to the equilibrium relative humidity of the salt. The effects of these cycles have been determined by a combination of gravimetric analysis, ion chromatography, and qualitative assessment of deposited material. Appropriate remedial action, based on a combination of desalination techniques and environmental control, is put forward for discussion.