Wanja Wedekind - Academia.edu (original) (raw)

Papers by Wanja Wedekind

SWBSS ASIA 2023, 2023

Continuous exposures to moisture and wetting-drying cycles lead to the concen- tration of salts a... more Continuous exposures to moisture and wetting-drying cycles lead to the concen- tration of salts and salt-induced damage in many externally exposed monuments and objects made of stone. However, the same forces of nature can also be used specifically for desalination.
In this case study a stone staircase with a balustrade was employed to perform a directed moisture. The procedure can be used with thin-walled parapets of histor- ical buildings, which often have a decorative function as well. The treatment presented in this article was realized on the staircase of the medieval town hall of the UNESCO World Heritage city of Goslar in Germany. The staircase with or- namental decoration was heavily affected by road salt.
Here, too, a desalination process with a directed water transport was used over a large area. In this case a hot lime mortar was applied as the poultice material. The rock properties and preliminary investigations of the salt content are present- ed and the desalination results are specified both qualitatively as well as quantitatively.

2004 wurden an der Südseite des Lutherhauses in Wit- tenberg die ruinösen Überreste des Wohn- ... more 2004 wurden an der Südseite des Lutherhauses in Wit- tenberg die ruinösen Überreste des Wohn- und Haus- haltstraktes, das sogenannte Annexfragment, entdeckt und ausgegraben. Die entdeckten Räumlichkeiten gelten als die einzigen noch erhaltenen authentischen baulichen Zeugnisse Luthers aus der Reformationszeit. Der Beitrag thematisiert den Diskurs zur Ruinenrestaurierung in der Denkmalpflege und stellt sowohl die Erhaltungsmaßnah- men am Annexfragment als praktisches Beispiel, als auch mögliche Materialien für eine denkmalgerechte Ruinen- restaurierung vor. Ziel der Restaurierung war es, durch minimalinvasive Eingriffe die Erhaltung des Baukörpers und seine statische Sicherung zu garantieren, ohne den eigenen Charakter des Objektes zu verfälschen.

One of the major causes for the dete- rioration of historical monuments made up of sandstones can... more One of the major causes for the dete- rioration of historical monuments made up of sandstones can be attributed to the circulation and evaporation of salt la- den fluids percolating through the rock material, an aspect that has been eit- her overlooked or neglected in previous restoration attempts, often with dama- ging consequences. Particularly the lack of consideration for the importance of a quantitative analysis of the salt content of the rock, has led to adverse effects in subsequent restoration attempts.
In the course of restoration of antique tombs no. 825 and 826 in the world he- ritage site of Petra the role of salt in the weathering process was fully taken into account and the restoration process exe- cuted accordingly.
With regard to the desalination two different methods were applied: the poul- tice method and the sprinkling method. The degree of desalination was in both cases intermittently measured until the concentration of the rock was evaluated to be low enough to initiate the restorati- on process with application of the selec- ted restoration mortar. Its condition was then probed by long term successive in- spections.
This study discusses the results and limits of both procedures and the techniques and methods applied in the course of the restoration of the two mo- numents.
Keywords: Petra, sandstone, salt weathe- ring, desalination procedures, restorati-
on mortar, restoration procedures, control of success

The use of volcanic tuffs as building elements in historical monuments built during the 17th, 18t... more The use of volcanic tuffs as building elements in historical monuments built during the 17th, 18th and 19th century are an important part of the cultural heritage in the city of San Luis Potosi, Mexico. For the constructions of the historical buildings pink-colored volcanic tuff rocks of the region were used, geologically defined as units of the “Cantera Ignimbrite”. This rock, locally also known as "Cantera Rosa" shows very different appearances and colors which can vary from pink to dark pink, grey, brown and orange. However these building rocks have significant variations in texture, compositions and mechanical properties and these properties determine the resistance to weathering and deterioration, because they show a wide range of deterioration types, e.g. scaling, flacking, sanding, back weathering and coloration/discoloration. Geological, petrophysical, geochemical and mechanical studies were realized on these rocks to understand the causes of their weathering and deterioration.
Keywords: tuff, Mexico, deterioration, porosity, pore distribution

Abstract The rock cut architecture of the Lycian culture in Turkey, created from around 500 BC to... more Abstract
The rock cut architecture of the Lycian culture in Turkey, created from around 500 BC to 400 AC, is one of the most fascinating remains of humanity’s ancient building heritage. The Lycian builders created monumental sarcophagi and tomb facades with unique forms and aesthetic styles which are never found twice in the Mediterranean world. Most of these magnificent monuments are cut into different limestone formations located in the area along the southern coast of Turkey, known as Lycia after its creators. The rocks as well as the monuments are affected by weathering and disasters, such as the dissolution and precipitation of calcite, biological growth and cracks due to earthquakes. To characterise the weathering forms and processes onsite investigations were done on rock cut monuments at the outstanding site known as Myra. Field investigations included quantitative mapping of damage phenomena, pointing surface hardness measurements utilizing a Schmidt pendulum hammer, water absorption using Karsten test pipes and closer surface observations using a digital microscope. The limestone varieties were characterised by petrophysical measurements and mineralogical analysis of thin sections.
Keywords: rock cut architecture, limestone, weathering, micro-climate, microbiology

The sandstone of the Michaelis Church in Zeitz shows a strong decay in form of relief and alveola... more The sandstone of the Michaelis Church in Zeitz shows a strong decay in form of relief and alveolar weathering. The main cause for the deterioration is an extreme salt attack by magnesium sulfate. The stone as well as the weathering forms were investigated. The alveoles were desalinated by using a sprinkling method and filled by a developed hot-lime mortar. Consequently, a concept of conservation could be formulated from all the investigations and the results obtained from the treatments that could be successfully applied in a test case.

In the present study a commercial hardness tester was used to evaluate the effectiveness of conso... more In the present study a commercial hardness tester was used to evaluate the effectiveness of consolidation on two monumental tombs composed of different sandstones. Furthermore different stone types were also repeatedly treated in a stepwise fashion and retested. The main goal was to determine whether it would be possible to detect even a small increase of consolidation by reloaded treatments. The results of the surface hardness tests on the stone samples correlated to their compressive strength. Tests were also conducted to determine whether a correlation between the increase of hardening of the surface in relation to the increase of the uniaxial compressive strength and ultrasonic velocity measurements exist. In an applied case study the consolidation effect has been verified after the consolidation of sandy stone parts with the same consolidant.

Contour scaling is the main weathering form observable at the Angkor monuments. In this study com... more Contour scaling is the main weathering form observable at the Angkor monuments. In this study comparisons are made between the building stone and crust material from the Phnom Bakheng Temple and fresh stone material used for restoration. A significant difference in hydric and especially in thermal expansion of the crust and sandstone is shown in this study. This leads to an extensional effect and is a force for delamination (scale formation). By using an object-specific conservation treatment, the hydric and thermal expansion of the crust material was reduced.

Moisture expansion in natural building stones is considered one of the most important factors aff... more Moisture expansion in natural building stones is considered one of the most important factors affecting their weathering and deterioration. The processes that may be responsible for the expansion under determinate relative humidity (hygric dilatation) and water-saturated conditions (hydric dilatation) are generally attributed to the presence of swellable clay minerals. In contrast to this assumption, our investigations show that moisture expansion also takes place in volcanic tuff building stones almost free from clay minerals. To provide a deeper understanding of the processes, swelling and deterioration were performed on 14 volcanic tuffs used as important building stones of different ages, compositions and weathering stages from Mexico, Germany and Hungary. The investigations undertaken include extensive chemical, petrophysical and fabric analyses. The samples show a wide range of effective porosity, microporosity, capillary water absorption, moisture expansion, and CEC values. High moisture expansion does not seem to depend on clay mineral content alone. We also observed that there is no significant effect on dilatation if clay minerals are present but only form a thin coat on the outer shell of bigger pores. Moreover, we identified a correlation between microporosity, average pore radius and moisture expansion. The investigations highlight the fact that moisture expansion cannot only be attributed to swellable clay minerals, and suggest that the presence and accumulation of micropores and their average radius and distribution play an important role for non-clay associated swelling intensity, which can most probably be attributed to the disjoining pressure.

ABSTRACT Water and moisture are some of the main decay agents of building stone and, in general o... more ABSTRACT Water and moisture are some of the main decay agents of building stone and, in general of any stone structure. Several non-invasive methods are used to quantify moisture in building stone, many of them based on the fact that moist stone presents different electrical properties than dry stone. This is the case of resistance-based sensing equipment, such as "Protimeter" portable moisture meters. Although originally designed to measure moisture contents in wood, this sensing equipment is commonly used to measure the so-called "Wood Moisture Equivalent" (WME) in other building materials, such stone and mortar. However, this type of resistance-based sensors pose a degree of uncertainty, as there are other factors that modify electrical properties, such as porosity and salt content. When assessing the overall state of decay of a structure, it might not be crucial, in some cases, to discern between salt and water content: both high moisture levels and high salt content give high WME values, and both are usually related to areas with overall poor state of conservation and/or more prone to decay. However, discerning these two factors is crucial when trying to understand the dynamics of how some decay patterns are formed. This is the case of surface runoff in vertical façades and how it leads to the formation of alveoli and tafoni through salt weathering. Surface runoff and associated salt weathering are among the main decay processes found at the archaeological site of Petra (Jordan) and its understanding is of paramount importance for the conservation of this site. Some "Protimeter" sensors include a capacitance sensor in addition to the usual resistance sensing pins, which allows to measure sub-surface electrical properties. This paper presents results on how the combination of these two measurement modes could be used to discern if high WME values are caused by high surface humidity or by high salt contents in the context of Surface runoff and associated salt weathering. Research funded by AECID (PCI A/032184/10)

Based on comparative investigations after a period of six years, a reduction of the ultrasonic ve... more Based on comparative investigations after a period of six years, a reduction of the ultrasonic velocity of 9% and 11% for two marble statues could be detected. The investigations on the objects were based on a newly implemented monitoring program using checklists and detailed mappings to document the development of the conservation state of the monumental statues in the historical center of Berlin, Germany. Traditional ultrasonic measurements were combined with surface hardness tests for selected representative areas using an equotip 3 device. In these areas, the water absorption was tested as well, using Karsten test pipes. In some areas and for different states of weathering, the results show a clear correlation between the surface hardness and the measured ultrasonic wavelength. The results of the water absorption tests underlined the differentiation of weathering forms. The investigations can help to characterize and distinguish between different forms of weathering, such as structural depth weathering or a softening close to the surface. By comparing the nondestructive and only minimal invasive test results with petro-physical compressive strength measurements of marble samples, a clear correlation between ultrasonic velocity, surface hardness, and capillary porosity could be identified. The results can help to calculate the stability assessment, plan the conservation, and make a prognosis of the ongoing weathering process. In conclusion, we elaborate a concept for conservation and restoration and make recommendations for a sustainable preservation of the sculptures.

The Santa Mónica Church of Guadalajara is an outstanding example of the Mexican baroque because ... more The Santa Mónica Church of Guadalajara is an outstanding example of the Mexican baroque because of its rich decoration. Typical regional building stones consisting of a yellow porphyritic tuff called the "Cantera Amarilla" were used to build the church.
Similar to many other buildings constructed with this material, the cut stones of the church also show back-weathering concentrated in the basement area, which can be traced to wet and dry cycles and the accumulation of salt. Conservation by desalination of the basement area was undertaken by cyclical sprinkling and measuring of the electrical conductivity of the excess water runoff. Using this method around 3000 grams of soluble salts could be extracted. During the restoration, diagnostic investigations were done consisting of mapping the deterioration, determining the moisture content and measuring the temperature as well as evaluating the salt accumulation by drilling powder analysis.
The mineralogical composition of the original stone material was determined by thin sections and X-ray diffraction (XRD) measurements. Investigations on the petrophysical properties focussed on the impact of wet conditions. Compressive and tensile strength tests were done under dry and water-saturated conditions as well as hygric and thermal dilatation, swelling pressure, water uptake, and sorption. To evaluate the impact of the inhomogenous internal structure, experimental testing of hygric swelling on a cubic stone block were performed.
The results from the study show that a reduction of the mechanical properties up to 40% by water saturation could be detected. Back-weathering is probably due to the inhomogenous internal structure, resulting from the interaction of clastic material and the fine-grained ash-matrix induced by different swelling intensities and swelling pressure.

Keywords: tuff stone, desalination, moisture expansion, critical values.

La restauración de edificios históricos erigidos con rocas naturales, es una tarea de un trabajo ... more La restauración de edificios históricos erigidos con rocas naturales, es una tarea de un trabajo multidisciplinario que incluye estudios fundamentales como los geológicos para conocer las propiedades y características de las rocas pero además es imprescindible entender su degradación y deterioro y saber cuales son los de procesos que los causa. Para poder restaurarlos es necesario tener conocimientos en conservación de rocas, los principios y métodos y los materiales para realizar una restauración.

In connection with the restoration of the Red Hall in the Neues Museum, located on the museums-is... more In connection with the restoration of the Red Hall in the Neues Museum, located on the museums-island in Berlin (2006-2008), a procedure for salt conversion and backfilling of hollow painted plaster areas with the help of low-pressure injection technology was developed and successfully implemented. The precipitation reaction resulting from the salt conversion was assessed using electrical conductivity measurements and identification of the precipitate by x-ray diffractometric analyses (XRD). For an additional securing of the plaster areas, an extensive injection was carried out and a suspension system for the back anchoring in the hollow
pot bricks was developed and implemented.

The former Franciscan monastery church was mentioned for the first time in 1266 and is located on... more The former Franciscan monastery church was mentioned for the first time in 1266 and is located on the periphery of the old town of Zeitz, Saxony-Anhalt, Germany. After several decades of neglect, the building was in the acute danger of collapse. In the 1990s parts of the roof collapsed and the
groin vaults of the church were exposed to bad weather conditions.
Along with the structural problems, the structurally damaging salts, principally magnesium sulfate, were regarded as the main cause of damage to the historical substance of the building. In many areas, the painting on the ashlar blocks and mortar was already lost or in acute danger of loss due to salt degradation.
After making a map of the damages and prior testing, the ribs and the vault stones were extensively desalinated by cyclical sprinkling in order to ensure a contact-free treatment.
In this case, the sprinkling proved to be both an economical procedure for a sustained salt reduction.

Natur / Stein / Kultur / Wein: Siegesmund, S., Hoppert, M., Epperlein, K. (eds.), 2014

Pori suntian dicita cones eicias molupta tureperiosam la consequ isimodist, simaio que conest ell... more Pori suntian dicita cones eicias molupta tureperiosam la consequ isimodist, simaio que conest ellut omni in essunde ipsum.

Proceedings of the ICOMOS-ISCS International Conference of Stone and Earthen Architectural Heritage

Konservierung, Restaurierung und Ergänzung im Neuen Museum Berlin - Zwischen ursprünglichen Intentionen und neuen Entwicklungen, 2013

SWBSS ASIA 2023, 2023

Keywords: tuff stone, desalination, moisture expansion, critical values.

Natur / Stein / Kultur / Wein: Siegesmund, S., Hoppert, M., Epperlein, K. (eds.), 2014

Proceedings of the ICOMOS-ISCS International Conference of Stone and Earthen Architectural Heritage

Konservierung, Restaurierung und Ergänzung im Neuen Museum Berlin - Zwischen ursprünglichen Intentionen und neuen Entwicklungen, 2013