Mitigation of salt damages by climate stabilization and salt extractions in the Crypt of St. Maria im Kapitol, Cologne

S. Laue & C. Schaab
In 1992-1996 an investigation was carried out to understand the salt damages in the crypt of St.Maria im Kapitol in Cologne: Damages of stones and wallpaintings have been caused by cycliccrystallization and dissolution of the salts halite [NaCl] and nitratine [NaNO3] due to climatechanges through heating the crypt. In the crypt the dissolution or crystallisation of halite andnitratine takes place when 65-75% of relative humidity is reached, depending on thethermodynamic properties of the saltmixture halite/nitratine....