Monument Future

110Deterioration assessment

For this activity, the building was divided in four main areas, the façades of Andes Street, 18 de Julio Avenue, Plaza Independencia and the Gallery (Figure 2). A total of 675 pieces were analysed. The basis used for this diagnosis is the classification proposed by ICOMOS (2011).

Table 4: Deterioration features present in Pilasters and Columns of Palacio Salvo (in brackets number of pieces with feature repaired).

The five deterioration families of this framework are present in Palacio Salvo (Tables 4 and 5). The Family Crack and Deformation is represented mainly by cracks and star cracks (Figure 3). Cracks occur very seldom in pilasters and columns, and only one is present in a step (Tables 4 and 5).

Splintering is the most frequent deterioration feature of the Family Detachment observed in Andes Street and 18 de Julio Avenue, followed by Chipping, which affects pilasters and columns of the four areas studied (Figure 4). Due to the location and characteristics of the latter features, they are a product of differential movement of the structure or the masonry, and not originated from low resistance of the rock. They are absent in steps.

Fragmentation is only observed in two panels of the Gallery. Blistering and spalling are related with features of other families and will be discussed at the end of the section.

Table 5: Deterioration features present in steps of Palacio Salvo (in brackets number of pieces with feature repaired).

111

Figure 4: a. Splintering, chipping, paint film, perforation and perforation with metallic insert in pilaster of Andes Street, b. Splintering with development of two parallel fractures.

Figure 5: Soiling in inner faces of Plaza Independencia columns: a. Partially “washed out”, b. Rock without deterioration beneath partially eroded soiling.

Features induced by material loss is the second most represented family, being rounding, perforation and missing part the ones which affect the higher number of pilasters and columns. Many perforations present metallic inserts, which causes very frequently oxide staining leading eventually to bursting (Figure 3). In the steps, rounding affects almost all pieces, abrasion and missing part a quarter of them.

The most represented family is Discolouration and deposit. Six subtypes of deposits are very frequently observed (dust deposit, paint, stick, cement, grease and pigeon droppings) in pilasters, columns and steps. Patina is frequent in small areas of the pieces. Soiling is very frequent in inner areas of pilasters and columns of the Gallery and Plaza Independencia, sheltered from rain and wind (Figures 5 and 6).

A deterioration association is observed in two felsic enclaves up to 40 cm in two faces of a highly exposed column of Plaza Independencia. The association includes bleaching, pitting, blistering, spalling and differential erosion, and is more advanced in the enclave which is frequently exposed to dog urine. This association is presumably related to the action of SO₂ product of air pollution, that causes feldspar kaolinsation and possible salt formation, as described by Schiavon (2007). Family Biological colonization is only represented by very seldom spider nets.

Other alterations are modification of the original basement ventilation elements, in Andes Street, 18 de Julio Avenue and Gallery. Most of them were transformed to access steps to business, which originally had no exterior access. These steps are made up of other rocks (Pan de Azúcar Syenite due to the similarity in décor) or monolithic (Table 5). Other category is “Strange elements”, including commercial posters, door numbers, etc.

A map of a column of Plaza Independencia is presented in figure 6. View I faces Plaza Independencia and is exposed, and View III faces the Gallery and is sheltered from rain and wind.

Figure 6: Deterioration map of Column 6 of Plaza Independencia (modified from FADU, 2019).

112Discussion and recommendations

There were no conservation programs developed in Palacio Salvo. Only minor reparations can be observed. In this study it is strongly recommended the design and implementation of a conservation program. Alternative nonaggressive measures are proposed if this program can not be developed.

Cracks related to splintering and chipping should be studied in detail to determine their cause. In general, cracks, fractures (with or without fragmentation), can be consolidated and mechanically repaired after cleaning and removal of loose fragments (Matero & Tagle, 1995). As consolidant Siegesmund & Snethlage (2011) recommend TEOS. For the repair of cuts, perforation, gaps and missing parts it is recommended to prepare patches of different colors, textures and materials, that can replicate the décor of Kösseine Granite, including the different enclaves observed. The metallic inserts should be removed by gentle mechanical means or by using a drill of small diameter to prevent damaging the rock around it.

Deposits weakly attached and spider nets should be removed by mechanical means (soft brush, plastic spatula). Soiling and deposits strongly attached could be removed by steam jet, as described in Siegesmund & Snethlage (2011). Oxide staining could be mobilized by chemical complexing or sequestering agents that can be soaked up or flushed away (Matero & Tagle, 1995). Following these authors, poultices with different chemical compounds could be used to remove oxide staining, grafitti, paint films, and eventually deposits of cement, and others that could not be removed by the previous methods.

Conclusions

The present study is the first documented case of a deterioration assessment of a dimensional stone façade in Uruguay performed by a geological team. The rock applied is identified as Kösseine Granite, of Wunsiedel, Germany.

No conservation program was developed prior to this study in Palacio Salvo, although minor reparations have been recognized. Using ICOMOS (2011) deterioration glossary, five deterioration families were recognized, being Features induced by material loss and Discoloration and deposit the most represented. Of the first family rounding, perforation (with and without metallic insert), and missing part are the most frequent, both in pilasters, columns and steps, being abrasion very frequent in the latter. They are all related with anthropogenic activities and not a consequence of poor rock quality. Of the second family, the most frequent deteriorations are deposits and soiling.

Other relevant alterations are replacement of original pieces in steps, mostly by monolithic and Pan de Azúcar Syenite, that matches the décor of Kösseine Granite. The good performance of Kösseine Granite in Palacio Salvo after 92 years of exposure is related to its excellent physical and mechanical properties.

References

IC-FADU (Instituto de Construcción, Facultad de Arquitectura, Diseño y Urbanismo) (2019) Propuesta de intervención para la conservación de las fachadas del Palacio Salvo.

Grimm WD (2018) Bildatlas wichtiger Denkmalgesteine der Bundesrepublik Deutschland. Ebner Verlag GmbH & Co.

Matero FG, Tagle AA (1995) Cleaning, Iron Stain Removal, and Surface Repair of Architectural Marble and Crystalline Limestone: The Metropolitan Club. J. Am. Inst. Conserv. Vol.34 I.1.

Morales Demarco M (2012) Mineralogical, Petrophysical and Economical Characterization of the Dimensional Stones of Uruguay; Implications for Deposit Exploration. Diss Univ Göttingen.

Mosch S (2008) Optimierung der Exploration, Gewinnung und Materialcharakterisierung von Naturwerksteinen. Diss Univ Göttingen.

Oyhantçabal P (2005) The Sierra Ballena Shear zone: kinematics, timing and its significance for the geotectonic evolution of southeast Uruguay. Diss Univ Göttingen.

113

2000 YEARS OF USE OF PLASTER AS BUILDING AND RESTORATION MATERIAL FOR THE „TAKHT-E SOLEYMAN“ IN WESTERN AZERBAIJAN, IRAN

Angela Eckart¹, Robert Sobott², Holger Kletti³, Toralf Burkert¹, Wolfram Jäger⁴

IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

– PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

1 Jäger Ingenieure GmbH, Paul-Schneider-Straße 17, 99423 Weimar, Germany

2 Labor für Baudenkmalpflege Naumburg, Rudelsburgpromenade 20C, 06628 Naumburg, Germany

3 Bauhaus Universität Weimar, Fakultät Bauingenieurwesen, F. A.Finger-Institut für Baustoffkunde, Professur Werkstoffe des Bauens, Coudraystr. 11B, 99423 Weimar, Germany

4 Jäger Ingenieure GmbH, Wichernstraße 12, 01445 Radebeul, Germany

Abstract

The preservation of the UNESCO World Heritage Site Takht-e Soleyman is supported by German experts who are working on the 114reinforcement of the badly cracked north wall of the west iwan (large audience hall). The building material gypsum which was used in the past is now also used for up-to-date repair work such as grouting and filling cracks and voids in the historic masonry. Locally quarried gypsum was used to produce a high-fired gypsum mortar in the traditional way. On the basis of laboratory experiments the activation of the hydration of anhydrite and the flow behavior of the mortar suspension was optimized.

Kewords: Ilkhanid palace, calcium sulfate phases, gypsum calcination, grouting, static safeguarding of masonry

Introduction

The UNESCO World Heritage Site Takht-e Soleymann (“Throne of Solomon”) is situated in the West Azerbaijan Province of Iran. The site lies 2200 m above the sea level and has a dry continental climate. In the 6th century AD under Sasanian rule a Zorastrian fire temple and palace complex was built at an artesian lake over the ruins of Achaemenid and Parthian buildings. After the end of the Sasanian dynasty in the 7th century AD the complex fell derelict. In 1221 the Mongols started the invasion of the Islamic world and about 1275 the site was used once again for the construction of an Ilkhanid summer palace. The greatest building within the palace complex was the west iwan, a vaulted audience hall, 11,5 m wide and 27 m long and closed on three sides (Naumann 1977, Huff 2006) which was lavishly decorated inside. With the decline of the Ilkhanid empire the buildings were abandoned and fell into ruin again. Beginning in 1956, the area was investigated by archaeologists and a restoration program was initiated with German support. A huge scaffold was erected on the east side of the west iwan in order to stabilize the ruinous north wall and stop the progressive decay. What was meant as a temporary measure is still in place and actually became an iconic landmark (Figure 1).

Since 2016 the preservation of the remains of the west iwan is part of a restoration project funded by the Cultural Preservation Program of the Federal Foreign Office. Experts are working on the reinforcement of the badly cracked north wall by strengthening the historic masonry with injection anchors and filling voids and cracks in the wall structure by mortar injections (Fucke, Hansen 2012, Bräunel 2016, Burkert et al. 2019). Gypsum mortar was used for the repair work because plaster is present in Sasanian as well as in Ilkhanid wall structures and its reaction with hydraulic cement mortar may cause the problem of sulphate attack. The project is aiming to strengthen of the wall so that it can withstand earthquakes in a seismically active region and the dismantling of the scaffold which is then no longer required.

Sasanian and Ilkhanid plaster

The historic multi-leaf masonry has a filling of stone rubble and mortar. The external leaf was built of travertine worked stones, rubblestones and bricks. Plaster was the binder for the mortar of all building periods and masonry types. Chemical and phase analyses of Sasanian and Ilkhanid plaster samples yielded fairly pure gypsum mortars. Maximum silicon dioxide impurities, mainly as quartz, did not exceed 8.3 mass%.

The thin section of a Sasanian gypsum mortar revealed a secondray very porous structure (Figure 2). The firing products are more or less dissolved, creating pore space which is surrounded by a gypsum matrix. Brown inclusions in the leached remnants of the fired gypsum must be regarded as impurities in the raw material.

Figure 1: North wall of the west iwan in the centre, Takht-e Soleyman.

Figure 2: Sasanian mortar with very porous structure and fragment of gypsum rock (plane polarized light).

Figure 3: Ilkhanid render with porous structure. The grains in the upper part of photograph exhibit distinct reaction rims (arrows); plain polarized light.

Embedded in the gypsum matrix are low quantities of gypsum rock fragments and brownish aggregate material with a maximum grain size of about 6 mm. Both may have entered the mortar as contaminants in the furnace or on the construction site. However, an intentional admixture as aggregates cannot be ruled out. Unreacted anhydrite was not detected.As the polarized light microscopy of thin sections showed, the Ilkhanid plaster is quite different from a Sasanian mortar. It contains still a lot of unreacted firing products with a maximum grain size up to 8 mm. Occasionally distinct reaction rims around the grains are visible (Figure 3). Both in the firing products and in the mortar matrix fine clayey (ceramic) particles occur. They most probably derive from impure raw material and not from the intentional admixture of crushed bricks as pozzolanic material. Like the Sasanian plaster the 115Ilkhanid plaster contains gypsum rock fragments with a grain size up to 8 mm. It cannot be decided whether they were added as aggregate or derive from insufficiently fired raw material. Overall, the matrix fabric of the Ilkhanid plaster appears to be denser than that of the Sasanian plaster due to the abundance of unreacted components.

Figure 4: Furnace for plaster production. Cross section (left) and view into the shaft with installation of temperature measuring device (thermocouple 1).