Salt Reduction/Desalination

Simple, qualitative testing of anions as sulfate, nitrate, and chloride is often insufficient to characterize the salt content of porous materials. Before and at several intervals after the conservation measure, it is important to determine the depth profile of both cations and anions. The salt uptake of the desalination material should also be recorded and, preferably, expressed in surface area and mass-related quantities.

Under normal laboratory conditions, homogeneous salination with sodium chloride of test bricks is very difficult. Therefore, the distribution of salts in brick samples must be monitored not only by weight gain, but also by quantitative depth profiles.

Physico-mechanical properties—such as density, water retention, and shrinkage of different desalination poultice mixtures—have been studied in the GCI laboratory. Mixtures of cellulose with kaolinite, bentonite, and Na-zeolite—as well as sand or light aggregate in different proportions—have been compared.

Project work includes comparing the efficiency of salt reduction methods (such as poultices, renderings, and rinsing) in the laboratory and in situ. In the field, the possibility of salt transport and deposition to zones adjacent to the site of the conservation measure should be taken into account as this can lead to secondary damage.

The project is also conducting quantitative analysis by ion chromatography and ion selective probe; these allow close monitoring of combined salt and moisture transport mechanisms. Measuring the salt uptake of poultice materials at different time intervals aids in the assessment of the different driving forces of mechanisms for wet (osmotic) and drying (capillary) poultices.

Completed Work

  • Establishment of a protocol for analysis.
  • Development of salination procedure and control of salt deposition.
  • Physico-mechanical characterization of different poultice materials.
  • Comparison between wet and drying poultices.
  • Comparative evaluation of efficiency for 7 different poultice mixtures.
  • In situ control of desalination.

Work in Progress

  • In situ validation of laboratory experiments and long-term control.
  • Salt and moisture transport experimental setup.
  • Testing of salt accumulating and resistant rendering.

Page updated: January 2011