Saving our old buildings from water damage

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  • Published: Sep 6, 2013
  • Author: Steve Down
  • Channels: NMR Knowledge Base / Raman / X-ray Spectrometry / Atomic / Base Peak / Chemometrics & Informatics / Proteomics / MRI Spectroscopy / Infrared Spectroscopy / UV/Vis Spectroscopy

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Water damages the stonework in old buildings, whether it seeps up from below or is deposited from humid air. Either way, once water penetrates into the body of the stone, it induces the formation of soluble salts which crystallise out to produce deposits on the surface, known as efflorescences. If the salt crystals are formed inside the stone, they cause stresses which can result in fractures, flaking and scaling. None of these outcomes are welcome in culturally important buildings.

The chemistry behind the damage is not clear, so a team of scientists from the University of the Basque Country in Spain decided to examine the stonework in a palace that has undergone water damage, to try and work out what happens inside the stone. Writing in Journal of Raman Spectroscopy, they tell how Raman spectroscopy and X-ray fluorescence were key to the success of their investigations.

The palace was a 15th Century building in the Basque country which had undergone several transformations in its history. It was constructed from sandstone and limestone and displayed many signs of disrepair, including efflorescences, sub-efflorescences (beneath the stone surface) and flakings. Using portable spectrometers, backed up by lab measurements of samples extracted from close to the sites of examination, they classified the metal salts present.

The original compounds in the stone consisted of sodium carbonates with different degrees of hydration, calcium carbonate, a mixed sodium calcium carbonate, oxides of iron and titanium, a silicate and quartz. However, degradation induced by water resulted in the formation of nitrates of potassium, calcium and sodium as well as sulphates of calcium and sodium. The discovery of these soluble salts should help restorers to make the right decisions when they come to work on the buildings.

This was illustrated clearly when the research team found that a mortar that had been used in a restoration step that was based on Portland cement actually promoted a new degradation process.

Although it would be convenient to use portable instrumentation to allow the buildings to be studied in situ, in practice the instruments were not sufficiently sensitive to characterise all of the salts present. However, the removal of pieces of stone might not be so critical because they would be taken from areas that are already damaged.

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