TEMOS – The Role of TEmperature, MOisture and Salts for Weathering Patterns
Moisture plays a key role in stone deterioration and is known as a main cause of damage to cultural heritage. The content of moisture in porous rock is extremely variable in time and space. These moisture amplitudes of rocks are recognized to evoke high weathering rates. Particularly small-scale fluctuations in moisture regimes are still insufficiently studied.
This PhD project combines field based and laboratory assessment to describe weathering processes and environmental-rock interactions at the rock-hewn cultural monument Uplistsikhe in Georgia. The research aims to overcome the lack of high-resolution data (temporal and spatial) on environmental factors related to weathering (mainly moisture, but also temperature, salts and rock parameters).
An interdisciplinary research method approach (with monitoring techniques / repeated field campaigns) will address weathering processes and assess environmental factors which constitute high weathering rates and damage to cultural heritage.
- Dr. Oliver Sass (principal investigator)
- Mag. Isabel Egartner (PhD student)
Knowledge of moisture fluctuations and salt behaviour is key for understanding weathering of artificial stonework. High concentration of moisture leads to a significant increase in deterioration rates and to the reduction of the mechanical resistance. The presented project deals with the processes involved in salt weathering at monuments made of limestone in Graz (Austria), Oxford (Great Britain) and “Lycia”, Turkey.
A multi-method approach we use a range of techniques:
- Mapping of weathering phenomena;
- ERT (Electrical Resistivity Tomography;
- Handheld Moisture Meter;
- Paper pulp poultices;
- Laboratory investigation (IC – Ion Chromatography).
- Egartner, I. & Sass, O. (accepted / minor rev.): Using paper pulp poultices in the field and laboratory to analyse salt distribution in building limestones. Heritage Science, revised Nov 2016.
- Egartner, I., Schnepfleitner, H. & Sass, O. (2014): Influence of salt and moisture on weathering of historic stonework in a continental-humid, urban region. In: Lollino, G., et al. (Eds.): Engineering Geology for Society and Territory Vol. 8: Preservation of Cultural Heritage (Springer). Proceedings of the IAEG XII Congress, September 15-19, 2014, Torino, Italy.
- Egartner, I. & Sass, O. (2015): Impact of salt and moisture on stone decay of cultural heritage. In: Hafbauer, C.K. (Ed.): International Academic Conference on Climate Change and Sustainable Heritage, Graz. Verlag der Technischen Universität Graz, ISBN 978-3-85125-389-4
As a pilot study we investigated an example of a cultural heritage structure in the continental-humid, urban region of Graz, Austria using a range of methods for moisture and salt monitoring. The aim was to assess the influence and the interaction between moisture and salts in the formation of the observed weathering structures of the involved marine limestones at the columns of the city gate ‘Paulustor’ in Graz.
2D-resistivity turned out to be a valuable tool for visualising moisture distribution in the investigated masonry. Furthermore, we used the handheld moisture sensor ‘Voltcraft MF-50 Moisture Meter’ to measure the moisture content of the wall surface at different heights along the vertical ERT Profiles on each side of the column. Paper pulp poultices were used as salt sampling method for non-destructive application. The resultant saline solutions were analysed using the ion chromatograph (Dionex ICS-3000 Reagent-Free) at the Institute of Applied Geoscience of the Technical University of Graz.
Intensive stone decay was observed at all four rain-shielded columns. Geoelectric profiles (Fig. 2.), supplemented by capacitive measurements and paper pulp poultices, show that both water and salt content are heightened in this area which is probably the reason for effective salt weathering. Water and salts (particularly halite) mostly derive from surface spray and to some extent from capillary rise; the shielded position prevents the salts from being washed down.
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