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

Abstract

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.

Archaeological ceramic amphorae from underwater marine environments: Influence of firing temperature on salt crystallization decay

“…These samples also display the largest desalination / non-desalination differences. This may indicate more intense alteration, inferred by the lower firing temperature (800 or <800ºC) and higher clay detected by 16 XRD (Fig.4) and sulfate content detected by IC ( Table 1). The higher SSA the greater the area exposed to weathering agents and more condensation can take place inside the pores of the materials.…”

“…After centuries immersed in this salty underwater environment, these artifacts pass to the aerial environment with totally different physico-chemical conditions when are extracted from the water. Fluctuations of relative humidity and temperature mobilize the absorbed soluble salts, modify the composition and texture and eventually the salt crystallization process accelerates weathering 15,16 endangering durability of these ceramics.…”

Fluctuations in the indoor environment in Spanish rural churches and their effects on heritage conservation: Hygro-thermal and CO 2 conditions monitoring

“…Material surfaces are known to be affected by abrupt changes in environmental temperature and humidity, for these two parameters govern the most common types of decay, such as wet-dry cycles [1,4,12], thermal shock [10] and surface or under-surface salt dissolution-crystallisation [13][14][15].…”

“…Moisture condensation may contribute to dissolving alkaline surfaces when the water vapour comes into contact with CO 2 flowing into the church through open doors or generated by human metabolism, use of certain heating systems or lit candles or incense [12,16,17]. Carbonate (lime mortars or limestone) and sulfate (gypsum or cement mortars) dissolution releases anions and cations that are carried inward where they precipitate as salts [14,15]. Another result of surface condensation and damp (in the presence of high humidity and moderate temperatures) is biological colonisation by fungi, bacteria or even insects that may cause biodeterioration in certain areas of the building [5,12,16].…”

Current Approaches in the Research of Dimension Stones:From Quarry to Heritage

“…The assessment of the behaviour of the stone after centuries exposed to the environmental conditions and anthropic aggressions highlights the importance of the petrophysic and geomechanical researches in order to avoid or mitigate the deterioration [9][10][11]. There are many examples of rapid deterioration when the stone does not meet the physical-mechanical standards, the stone mineralogy was not considered, or the building process was deficient [12].…”