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A closer look at salt loaded microstructures

M.R. de Rooij and C.J.W.P. Groot
Delft University of Technology, Delft, The Netherlands

Many walls of ancient buildings are covered with plaster layers. Amongst the most recurrent causes of damage of plasters and substrates are moisture and salt decay processes. To combat these salt problems, special salt resistant plasters have been developed for application on salt loaded substrates. However, experience in the field has shown that failures regularly occur on these special mortars, making the situation little transparent for end-users.
A European project called COMPASS has addressed this particular problem in a large number of plasters and renders in terms of their performance under severe salt load. This paper describes in more detail the relation that has been observed between salt transport and salt crystallization versus the microstructure (both permeability and composition) of both the plaster and the substrate. Field samples and laboratory tests are discussed. It is shown that the microstructure of both the plaster and the substrate do play a significant role in the transport and crystallization of salt.

Key words: Renders, plasters, substrate, pore size distribution, halite (NaCl)