Sawdy, Alison:

Salt and Moisture Transport in Porous Media

The history of conservation is littered with incidences of failed treatments, and indeed it is one of the greatest ironies that we face, that our well intended actions sometimes result in making a bad situation worse. This is particularly true in the context of salt deteriorated objects. Indeed here particular care is required, since the medium that is most often used to treat the object (i.e. water) is precisely that which is responsible for activating damage. Salt damage is a multi-factor problem, resulting from the interplay between the nature and structure of the porous object, the physical and chemical behavior of the salt solution, and the prevailing context, i.e. the environmental conditions.
The degree and type of damage caused is strongly related to the location of salt accumulation and crystallization, which in turn is affected by salt and moisture transport processes that take place within porous media. Therefore, the selection of an appropriate treatment method for tackling salt deterioration (particularly when using water based systems), requires a fundamental understanding of the nature of salt and moisture transport within porous media, and the principle factors that affect this. This paper examines the current scientific understanding of salt and moisture transport processes in porous media, in the context of practical conservation methods such as poulticing. In particular, the principle factors that affect the transport and accumulation of soluble salts during poulticing treatments will be examined.

Alison Sawdy Heritage is a chemist and wall paintings conservator (BSc hons environmental chemistry, University of Edinburgh, 1989; DipCons wall painting conservation, Courtauld Institute of Art, 1994; MSc paintings conservation, University of London, 1995; PhD, Institute of Archaeology, University College London, 2001). She is an Accredited Conservator Restorer (Institute of Conservation) and an editor of Studies in Conservation. A collaborator on several EU projects, including the EU FP6 project ‘Desalination’, her main research interests are assessment and treatment of salt damage in wall paintings, and the diagnosis of environmental causes of deterioration.

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