A System to Simulate Polluted Atmospheres and Its Application to the Study of Stones Used in Andalusian Cathedrals and of Treatment Products

Sánchez, Rosario Villegas; Parapar, J. F. Vale

doi:10.1179/sic.1994.033

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“…The original source of magnesium present in magnesium sulfate efflorescence is generally tied to be the composition of the building materials used for construction, mainly dolomite or magnesium limestone (Shaffer RJ 1932;Caner et al 1985;La Iglesia et al 1994;Villegas et al 1996) as well as magnesiumrich mortars (Lauri et al 1925;Charola and Lewin 1979;Klemm and Siedel 1996;González-Limon and Buergo Ballester 2002;Tulliani et al 2005;López-Arce et al 2009a).…”

Section: Introductionmentioning

confidence: 99%

Preservation strategies for avoidance of salt crystallisation in El Paular Monastery cloister, Madrid, Spain

et al. 2010

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The cloister from El Paular Monastery is highly affected by salt crystallization of Mg-sulfates and presence of chlorides and nitrates. In order to avoid salt crystallization, the consequent deterioration of building materials and to keep the stability of some significant paintings that will be exposed inside the cloister, after the characterization of building materials and salts, three preservation strategies has been established based on architectural, pethophysical and physical-chemical features.The main source of Mg-sulfate salts is the high concentration of moisture and raising damp by capillarity, especially through the mortars which are the most porous materials. The dissolution of gypsum (Casulfate) as component of the mortars and its interaction with magnesium from the mortars, granite and dolostone give rise to Mg-sulfates that migrate through the porous building materials. The installation of a ventilation system would avoid the rising damp and hence the dissolution, mobilization and crystallization of salts. The salt reduction of building materials have been performed with cellulose poultices with pores between 15-20 m and between 10 and 30 m diameter. The monomodal distribution and smaller pores of dolostone (1 and 3 m) and mortars (0.1 and 10 m) is the cause of the lesser effectiveness of salt reduction in these materials compared to the granite, with a polymodal pore size distribution and pores distributed in the range 100-300 m. A higher number of cellulose poultice applications could increase the efficiency of this desalination procedure. However, there is no a warrantee of the total extraction of salts and the mixture of this cellulose poultice with clays to shift the PSD to smaller sizes would be more efficient to desalinate dolostone or mortar. The most suitable environmental conditions, inferred from thermodynamic model predictions (Runsalt software) and experimental work based on relative humidity transfer inside the stone, predict that to avoid salt crystallization these values would be 17º±2ºC and 55±2% RH.However, if there are some failures in the ventilation system or in the environmental control we recommend keeping the paintings to be exposed on the walls of the cloister inside glass cases. This research represents both a practical and experimental work useful for conservation scientists and restorers involved in the field of preservation of monuments and environmental impact to avoid salt crystallization.

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