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Predicting environmental conditions to minimise salt damage at the Tower of London: a comparison of two approaches


The paper compares the results of two studies of salt damage at the Wakefield Tower, Tower of London. The first, in 1993, was based on semi-quantitative salt analysis and hygroscopicity measurements. The second was based on quantitative analysis and a thermodynamic model, ECOS. Both studies aimed to predict environmental conditions that would minimise salt damage to the interior stonework. Their predictions are markedly different, and this paper examines the reasons for the differences. It is shown that hygroscopicity alone is not a reliable indicator of crystallisation from mixed salt solutions.

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  1. Steiger has queried the detailed ECOS predictions, noting that anhydrous calcium nitrate is stable only below about 10% RH, and that ECOS seemingly omits the double salt KNO3.Ca(NO3)2.3H2O. Nonetheless, he does not consider that the main conclusions are affected (Steiger, Institut für Anorganische und Angewandte Chemie, Universität Hamburg, personal communication, 2006).

  2. data from London City Airport, 9 km from the Tower and, like the Tower, beside the River Thames.


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I am grateful to Laura Church for undertaking the analyses and to the Natural Environment Research Council for use of ICP-AES and IC facilities. Petros Prokos suggested the removal of calcium to balance the charges in RUNSALT, and Michael Steiger calculated the predicted hygroscopicities. I am grateful to Historic Royal Palaces for the opportunity to undertake the research and to publish the results, to Kathryn Hallett for generously providing the environmental data, and to Konrad Zehnder and an anonymous referee for their constructive suggestions.

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Correspondence to Clifford A. Price.

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Price, C.A. Predicting environmental conditions to minimise salt damage at the Tower of London: a comparison of two approaches. Environ Geol 52, 369–374 (2007).

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  • Stone
  • Conservation
  • Salt
  • Environmental control
  • Hygroscopicity