Crystallisation repeated cycles

Stabilisation by climate control. The most desirable method to prevent damage induced by the repeated cycles of crystallisation and hydration would probably be environmental control. However, neither the selection nor the maintenance of such an ideal environment is possible if looked at realistically. Predictions of salt crystallisation and hydration from mixed salt solutions are more or less impossible, taking into account all the different parameters that influence the process. Sawdy provides a brilliant overview of the subject and considers relative humidity, temperature, air movement, type and structure of the porous support, salt mixture composition and salt concentration. It is necessary to consider not only consolidation treatments of the plaster or the paint layer, which as such may influence the transition behaviour of the salts, but also the influence of microbial extracellular slimes on the porosity of the system. 

If the cycle is then repeated, during the evaporation stage the sodium chloride is precipitated (and removed ) whilst the concentration of the nitrate re-attains 160 kg/100 kg water. On cooling again, the amount of sodium nitrate which crystallises out is 91.7 kg/100 kg water,... 

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