Salt damage and RH changes: The case of the Waag Building in Amsterdam

Changes in the air RH can cause damage to building materials contaminated with hygroscopic salts, even in the absence of any other moisture source. This phenomenon has been observed in the case of the Waag building in Amsterdam, affected by severe salt decay. The investigation, carried out by means of different techniques (e.g. ESEM-EDX, IC and XRD), has revealed the presence in the masonry of a large amount of hygroscopic salts (mainly sodium chloride and nitrates) and the absence of any moisture sources other than the RH of the air. Besides, an adsorption experiment performed on samples from the building has pointed out the hygroscopic moisture uptake of the salt mix even at low RH. These results, in combination with a monitoring of the interior climate for a period of about 1 year, have allowed to conclude that the damage observed is due to the frequent RH changes through the equilibrium where dissolution/crystallization of the salt mix takes place. On the basis of these findings an advice for the conservation of the building was given. In: Bauinstandsetzen und Baudenkmalpflege Vol. 13, No. 4, 241–250 (2007)