Schwarz.etal 2008

Hans-Jürgen Schwarz, Erwin Stadlbauer, Rolf Niemeyer (2009): Diagnostic investigations to define the possibility and the effectiveness of desalination with the poultice-technique - a case study.- In: Ottosen, LM. et al. (Eds.), Salt Weathering on Buildings and Stone Sculptures. Technical University of Denmark, Proceeding of the conference in Copenhagen 22-24 October 2008, pp. 237-248

Keywords

Desalination, wall painting, Mirowski method, droplet method, poultice.

Abstract

The contamination of the walls, especially the surfaces with salt and a salt solution is often one of the biggest problems concerning the conservation concept of wall paintings. A good example for that is the Cathedral in Königslutter in Northern Germany. The wall paintings of the Cathedral in Königslutter go back to a medieval wall painting, which was painted over at the end of the 19th century. In the second half of the 20th century large amounts of cement suspension were injected into the walls to stabilize the static of the building, which started the damaging process essentially by salt crystallisation at the inner surfaces of the cathedral. After the outbuilding was completely repaired in 2006 the conservation of the wall paintings, plasters etc. in the cathedral begun. The analyses of surface samples and the drill - sampling show a high salt content consisting of sulphate and calcium ions, nitrates (mostly together with potassium but also with calcium) and rarely chloride and sodium. Salt efflorescences are often made of gypsum partially together with Calcite as a sinter crust. Fluffy efflorescences consist of niter. The total amount of salt only in some cases decrease with the depth of sampling. To extract the salts in the wall painting and in the plaster the poultice method was chosen. Before applying this method the surfaces have to comply with the requirements for a successful application e.g. the moisture transport characteristics. The results show clearly that the first plaster layer, which is slightly hydrophobic in some parts, very slowly transported moisture. Despite the low moisture transport rates the poultice method was tested, because salt action is the most damaging process. The application tests show that only a small amount of salt can be extracted.

Volltext

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