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CHARACTERIZATION AND DETERIORATION ASSESSMENT OF KÖSSEINE GRANITE IN PALACIO SALVO, MONTEVIDEO, URUGUAY
Manuela Morales Demarco, Eloísa Cocorel
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.
Instituto de Ciencias Geológicas, Facultad de Ciencias, Universidad de la República, Uruguay
Abstract
In Uruguay, one of the most important buildings is Palacio Salvo. The present research is part of a diagnosis for the definition of an interdisciplinary project of intervention for the revalorization and conservation of its façades.
These activities started with the identification of the rock used as Kösseine Granite, of Wunsiedel, Germany. This rock is applied as polished pieces and most of them show, as deterioration features, rounding, missing parts, perforations with or without metallic inserts, often surrounded by oxide staining, deposits and soiling. Some plates eventually show up to 20 cm cracks in the edges related to splintering, chipping and two large plates are crossed by 80 cm fractures. Pieces used as steps show abrasion, rounding, and fractures in the edges causing missing parts.
Exterior and paving are among the most demanding applications of dimensional stones. Nevertheless, Kösseine Granite presents a good performance and its state of deterioration is low.
Keywords: Historical and cultural heritage, Kösseine Granite, Uruguay
Introduction
One of the most iconic buildings in Montevideo is Palacio Salvo, in the heart of the city: 18 de Julio Avenue and Plaza Independencia. Built between 1922 and 1928 by Mario Palanti, an Italian architect, it was commissioned by Salvo brothers.
In the declaration of Palacio Salvo as National Historical Monument, in 1996, it is clearly stated the relevance of its preservation and recovery (Presidential Resolution N° 1144/996, Uruguay). In this sense, an agreement was signed between the company owner of the building, Palacio Salvo S. A., and FADU (Facultad de Arquitectura, Diseño y Urbanismo – Universidad de la República) for a study for the conservation of its façades (IC-FADU, 2019). The ICG team (Instituto de Ciencias Geológicas, Facultad de Ciencias) was assigned a 3-month period the deterioration assessment of the granitic external façade of the ground floor.
Identifying the granitic façade
For the general registration of the rock applied and its deterioration assessment, the recommendations of the working group “Natural Stones and Weathering” (2019) of Aachen University were followed. It 108was not possible to map the entire external façade due to time constrains of the study, therefore only four sections of the building were mapped.
There was some controversy about the origin of the rock applied. In the Uruguayan small geological community, it was believed it was a facies of Pan de Azúcar Pluton. This pluton, studied in detail by Oyhantçabal (2005), is a km-size syenitic, quartz-syenitic and granitic circular intrusion, historically exploited with ornamental purpose (Morales Demarco, 2012). All efforts to localize the variety supposdly applied in Palacio Salvo in the area of the pluton were unsuccessful.
At the beginning of this study, 15 blueprints of the entire granitic façade were found by FADU in the General Archive of the Nation (Archivo General de la Nación). These blueprints have the localization and dimensions of around 1,000 pieces of the granitic façade of Palacio Salvo (the external façade and the façade of the passage, not studied in the present work), and some inscriptions written in German: Kösseine Granit Poliert, Grasyma Wunsiedel, Januar 1925.
The ICG team compare the dimensions of the pieces applied in Palacio Salvo, with those stated in the blueprints. The match is perfectly accurate. Simultaneously, a communication with the German company allowed the confirmation as the providers of the rock and the undoubtedly identification as Kösseine Granite (Figure 1).
Characterization of Kösseine Granite
Petrography
Due to the impossibility of sampling the rock in the buidling, as it is a National Historical Monument, a preliminary petrographic characterization was performed in situ. It is a very coarsed-grained leucocratic rock, yellowish white, to beige and greyish light brown. This is not the typical color of Kösseine Granite, but a yellowish variety that is also widely used in Germany.
The rock shows a porphyritic texture, due to the presence of alkali feldspar up to 3.5 cm, most around 2 cm, subhedral, frequently rounded. Some show zoning with a light brown core, sometimes euhedral, surrounded by a greyish white mantle. Most are grey. Inclusions of biotite (Strohmeyer, 2003) are very frequent, often evidencing growth rims. Occasionally, a translucent mineral can be observed, that gives the rock a pearl luster, this is probably plagioclase.
Figure 1: Right: Brochure of Palacio Salvo in construction with promotional poster of Grasyma (courtesy of Claus Wölfel).
Quartz is interstitial between feldspar and biotite, with light brown to beige color. Biotite shows sometimes hexagonal sections with dark reddish to coppery color. Muscovite is silver grey sometimes with greenish hues. Both minerals frequently form nests, and the biotitic sometimes show orange oxidation rims.
Garnet is present as an accessory mineral in mm euhedral to subhedral red crystals with vitreous luster. They occur occassionally as inclusions in alkali felspars, sometimes in matrix minerals.
Table 1: Mineralogical composition of Kösseine Granite.
| Mineral (%) | Grimm (2018) | Strohmeyer (2003) |
| Alkali feldspar | 41 |
