NaCl-related weathering of stone: the importance of kinetics and salt mixtures in environmental risk assessment

Sebastiaan Godts*, Scott Allan Orr, Julie Desarnaud, Michael Steiger, Katrin Wilhelm, Hilde De Clercq, Veerle Cnudde, Tim De Kock

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Salt weathering is one of the most important causes of deterioration in the built environment. Two crucial aspects need further investigation to understand the processes and find suitable measures: the impact of different climatic environments and the properties of salt mixture crystallization. We demonstrate the importance of kinetics in quantifying crystallization and dissolution cycles by combining droplet and capillary laboratory experiments with climate data analysis. The results proved that dissolution times for pure NaCl are typically slower than crystallization, while thermodynamic modelling showed a lower RHeq of NaCl (65.5%) in a salt mixture (commonly found in the built heritage) compared to its RHeq as a single salt (75.5%). Following the results, a minimum time of 30 min is considered for dissolution and the two main RHeq thresholds could be applied to climate data analysis. The predicted number of dissolution/crystallization cycles was significantly dependent on the measurement frequency (or equivalent averaging period) of the climatic data. An analysis of corresponding rural and urban climate demonstrated the impact of spatial phenomena (such as the urban heat island) on the predicted frequency cycles. The findings are fundamental to improve appropriate timescale windows that can be applied to climate data and to illustrate a methodology to quantify salt crystallization cycles in realistic environments as a risk assessment procedure. The results are the basis for future work to improve the accuracy of salt risk assessment by including the kinetics of salt mixtures. [Figure not available: see fulltext.]

Original languageEnglish
Article number44
Pages (from-to)1-13
Number of pages13
JournalHeritage Science
Issue number1
Publication statusPublished - 14 Apr 2021


  • Built heritage
  • Crystallization
  • Damage prediction
  • Porous materials
  • Salt mixture
  • Sodium chloride
  • Weathering


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