Salt efflorescence in historic wooden buildings

Abstract

Efflorescence and subflorescence are frequent phenomena occurring in buildings of porous inorganic materials such as bricks, stone, and concrete. Since the above phenomena have detrimental effects, they were the subject of detailed physicochemical investigations. Efflorescence on wooden material was commonly observed on collection artefacts treated with preservatives such as inorganic salts or organic pesticides. Occurrence of efflorescence in historical wooden buildings was less studied although it could cause serious conservation concerns. This paper describes an examination of chemical and mineralogical composition of salt efflorescence in wooden buildings. In situ analysis by X-ray fluorescence spectrometry was followed by investigation of plain efflorescence by infrared spectrometry, X-ray diffraction, electron microscopy, and electron probe microanalysis. Quantitative analysis of purified efflorescence was performed by plasma atomic emission spectrometry, ion chromatography and absorption spectrophotometry. In addition, depth-profiling of characteristic ions in wood was performed. The objects of study were a series of log houses of the Sverresborg Trøndelag Folk Museum in Trondheim, Norway. It was found that the efflorescence in these buildings includes a series of metal ions, the most abundant being Al . In addition the ammonium ion is present in a large amount. The single detected anion is sulfate. Actually, the efflorescence consists of a mixture of simple and double sulfate salts of alum and Tutton's compound types. Identified Tutton's compounds are mohrite ((NH 4 ) 2 Fe(SO 4 ) 2 ·6H 2 O), ammonium zinc sulfate hexahydrate ((NH 4 ) 2 Zn(SO 4 ) 2 ·6H 2 O)), and boussingaultite ((NH 4 ) 2 Mg(SO 4 ) 2 ·6H 2 O)). Among the alums, both tschermigite (NH 4 Al(SO 4 ) 2 ·12H 2 O), and potassium alum (KAl(SO 4 ) 2 ·12H 2 O)) were detected. The composition of efflorescence suggests that the wooden material was treated with a blend of sulfate salts ((NH 4 ) 2 SO 4 , Al 2 (SO 4 ) 3 ·18H 2 O, MgSO 4 ·7H 2 O, FeSO 4 ·7H 2 O, ZnSO 4 ·7H 2 O, and Na 2 SO 4 ·10H 2 O)) for protection against fire and biological degradation. The efflorescence appeared as a consequence of water leakage through the roof that led to the dissolution of the salts contained in the wood, followed by evaporation and salt crystallization at the surface in the form of double sulfate salts. Although the occurrence of efflorescence in this case was accidental, a natural and more frequent cause of efflorescence could be the deliquescence of inorganic preservatives impregnated in the wood.

A natural ancestral saltwater treatment to modify the technological properties of date palms

“…This salt leaching shows that the permanency of soluble salts is only satisfactory in the indoor where the material is not exposed to water. As expected, Catelli et al (2016) proved that the salts were washed out by precipitation from the outdoor areas. This added durability might be useful for preventing the development of decay in service, although it is difficult to assess the benefits of such salt loadings when the risk of leaching is high.…”

Conservation issues and chemical study of the causes of alteration of a part of the Stave Church in Hopperstad (Norway)

“…It was also thought that the layer could be caused by efflorescence of salts. This is a common phenomenon for buildings and can be a result of a previous treatment of the building material [11,12]. A previous pesticide treatment was also considered as a possible source.…”

“…Certain types of salt can cause more damage than others to different materials. Knowing the chemical composition of the salt is, therefore, only one of the important factors necessary to assess the true harmfulness it might have on the materials [11]. The layer on Hopperstad Stave Church could possibly be harmful for the wood and metal in the long term, especially when the materials are unprotected by the tar.…”

Mold Odor from Wood Treated with Chlorophenols despite Mold Growth That Can Only Be Seen Using a Microscope

“…All wood was treated in the crawlspaces below schools A and B, and there was no wood rot. Furthermore, no visual mold growth was found, with the possible exception in school A of some areas in the treated ceilings with a patchy thin white substance that could be mold but more likely was salt residue from preservatives [ 98 ]. Seven samples of treated wood were taken from school A and eight from school B.…”