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Desalination of masonry

Salt may damage masonry and plaster. Salts in masonry may be originally present in the materials or may have penetrated later from external sources such as rising groundwater and sea-salt spray. Salt crystallization in dry periods may cause powdering, scaling, or crumbling of brick, natural stone and mortar. Reducing the salt content in the masonry by desalination helps prevent damage and preserve valuable historic materials.

Whereas salts may be extracted from sculptures by immersion in water, salt-loaded masonry requires a different approach. Salt extraction involves applying compresses of clay, cellulose powder and water to the wall. The water dissolves the salts as it penetrates the wall, and the salt solution is transported from the wall into the compresses in the drying process. The treatment is repeated until the salt content in the wall is reduced to a safe level.

Unfortunately, this complex technique is not always effective. As part of the EU Desalination project, TNO is investigating the optimum composition of the desalination compresses: what types of clay and proportions of ingredients work well on a given substrate? Part of the study is the treatment of a historic Amsterdam building, De Waag, where priceless masonry master's pieces have been affected by salt. The findings will lead to guidelines and recommendations for the right mixture to be used in each specific situation.


Dr. Timo Nijland

  • Built cultural heritage
  • monuments
  • conservation
  • natural stone
  • buildig materials


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