Alveolarverwitterung und Schichtparalleles Auswittern der Kreidesandsteine der Kirche von Leuba/Sachsen

Alveolar (honeycomb) weathering and weathering out are present on different varieties of sandstones at the church of Leuba (Saxony). In order to create an appropriated conservation concept, it was necessary to investigate the damage processes. Considering measurements and analyses of the pore structure and the salt content together with the investigations on-site like drill resistance and capillary water uptake, it is possible to explain the processes of alveolar weathering and weathering out of the building stones in Leuba. Air highly polluted with SO (sub 2) and the use of dolomitic lime mortar are the sources of salt ions, which are accumulated step-by-step in the micro-pore system of the weathered areas. The deterioration rises by cyclic salt crystallisation of predominantly magnesium sulphates crystallizing in different hydrates which is controlled by the ambient relative humidity. The weathering process is forced when the salts are concentrated in the back-weathered area and sheltered from rainwash. To close the holes loaded with salt and to avoid further damage, stone repair mortars have been suggested which are appropriate for the pore system of the sandstone and to a certain extent resistant against salt attack.

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