The role of marine aerosol in the formation of (double) sulfate/nitrate salts in plasters

Abstract

During decades the use of gypsum in different buildings has been very common, especially in the Atlantic lands of Europe. Decay compounds like salt crystallizations are ones of the principal deterioration factors of such historical buildings. In this study, gypsum-based plasters from different inner rooms of the Igueldo Lighthouse (San Sebastian, Spain), a building dated back to 1860 that has been subjected to several repairs within these years, were investigated in order to ascertain the main mineral phases produced during the weathering process. A combination of Raman spectroscopy, X-ray diffraction, infrared spectroscopy in ATR mode, SEM-EDS imaging and Raman imaging was successfully applied to study the distribution of different decay compounds in the gypsum-based matrix and to establish the decay reaction pathway which leads to the formation of the identified decay compounds. Additionally thermodynamic chemical modeling was also performed to explain the formation of specific decaying compounds. According to the location of Igueldo Lighthouse (just above a cliff, close to the sea), this building experiments a wide influence of the marine aerosol (Na + , K + , Mg 2+ , Cl − and NO 3 − input) and the influence of a high damp environment, giving rise to common efflorescence salts as well as to different mixed-calcium sulfates and mixed sulfate-nitrate salts, such as glauberite, syngenite, polyhalite and humberstonite. Dehydration process of gypsum from the plaster (leading to the presence of anhydrite and bassanite) was also identified.

On‐site Raman study of artwork: Procedure and illustrative examples

“…The sensitivity of Raman spectroscopy for low crystallized phases and the microscopic resolution fulfils the requirements for protective ability index's calculations for complex and heterogeneous corroded layers. Madariaga's group demonstrated at the laboratory and with appropriate software that the portable spectrometer is very useful to select the most representative spots for sampling and comprehensive study …”

“…Stone and plaster corrosion are also important questions where Raman studies can help understand mechanisms and solve problems. Using measurements being made at the laboratory on sampled fragments, Morillas et al showed that a combination of X‐ray fluorescence and Raman on site measurements is sufficient to draw conclusions. A rather similar approach can be taken for bronze artefacts and for glass (but at smaller scale).…”

Portable and Raman imaging usefulness to detect decaying on mortars from Punta Begoña Galleries (Getxo, North of Spain)

“…The results presented in this work evidence the necessity of combining Raman results with the ones extracted with additional techniques in order to contrast and complement the Raman evidences . Sometimes, the Raman bands obtained are very weak; thus, the assignations performed using these techniques can be uncertain.…”

“…XRD analyses were performed using a diffractometer (PANalytical Xpert PRO, Almelo, The Netherlands) provided with a Cu tube ( λ Cu k α average = 1.5418 Å, λ Cu k α 1 = 1.5460 Å and λ Cu k α 2 = 1.54439 Å), a vertical goniometer (Bragg‐Brentano geometry), programmable divergence slit, automatic sample exchanger, secondary graphite monochromator and PixCel detector. Additional information of the instrument and measurement conditions can be revised elsewhere …”

Evaluating sulfates and nitrates as enemies of the recent constructions: Spectroscopic and thermodynamical study

“…Evaporation will cause the saturation of a solution, and this relies on the temperature, the relative humidity (%RH) of the environment, and the chemical composition of the solution . Variations in %RH and temperature around or inside buildings play an important role in the crystallization or dissolution of different salts …”