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article imageSalt-Gobbling Bacteria Save Historic Masonry

By Grit Buettner     Jan 25, 2002 in Technology
WISMAR , Germany (dpa) - Scientists at Wismar University have discovered that salt-eating bacteria can save old walls. The one-year laboratory research project revealed that certain micro-organisms can eliminate salt and dampness from buildings without causing any structural damage.

The musty smells of an underground crypt can be banished for good, says Professor Helmuth Venzmer, the university's resident structural physicist and director of Wismar's Dahlberg Institute for the Analysis and Restoration of Historic Buildings.

Venzmer's research group latched onto the source of the damp brickwork in the course of their work finding salt to be the culprit. It accumulates in high concentration on the surface of buildings as water evaporates. The nitrates in turn draw moisture from the air - just like a household saltcellar - and keep the walls permanently wet.

So before any restoration work can begin, the walls are rid of dampness by the microscopic "salt-eaters", explains Venzmer.

The research team he heads and the new biological method to desalinate masonry it has presented was funded by the German Centre for Crafts and Preservation of Historic Buildings and Monuments in Fulda (Hesse state), Hamburg University, a textile research company in Rudolstadt (Thuringia state) and the German Federal Foundation for the Environment in Osnabrueck.

The process involves moistening lengths of materials in which a special kind of anaerobic bacteria (one that does not require oxygen) is implanted. The prepared material is then draped over walls or columns suffering from excess salt content as a kind of biological compress.

The bacteria require several weeks to consume all the salt from the masonry, turning the nitrates first into nitrite and then finally into nitrogen. This escapes as a gas, leaving behind the desalinated structure and dying bacteria with nothing to eat.

The new method is especially suited for ancient buildings and monuments because it maintains the original brickwork, unlike chemical methods or, if the worst comes to the worst, demolition.

"This methods means that masonry surfaces can actually be saved," says Ewa Prync-Pommerencke, head of building preservation for the state government in Schwerin. "However, the wet compresses are not suitable for walls covered by plaster or paint."

The scientists contend that half of all historic buildings in Germany needing renovation suffers from dampness and surface saline concentrations.
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