THE TRON KIRK,
EDINBURGH
INVISTIGATION INTO SANDSTONE PROPERTIES AND DECAY
WASEEM ALBAHRI
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Figure 01: Drawing of the Tron Kirk north elevation
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THE TRON KIRK,
EDINBURGH
INVISTIGATION INTO SANDSTONE PROPERTIES AND DECAY SCOTTISH CENTER FOR CONSERVATION STUDIES MSc Architectural Conservation AC5: Conservation Technology Leader: Dr. Dimitris Theodossopoulos Tutor: Dr. Audrey Dakin Researcher: Waseem Albahri
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CONTENTS:
Figure 02: North west view of the Tron Kirk
Contents:
04 Page
1. Introduction 1.1 Scope and Limitation of the report 1.2 Overall Assessment of Condition
06 06 06
2. The Tron Kirk Site Profile 2.1 Site Plan 2.2 Vital Statistics 2.2.1 Address 2.2.2 Ownership 2.3.3 Listing
08 08 08 08 08 08
3. Brief Historical Description of the Tron Kirk 3.1 Early Construction of the Tron Kirk 17th Century 3.2 Later Alternations in the 18th and 19th Centuries 3.3 Modern History of the Tron Kirk (20th - 21st Centuries)
10 10 11 12
4. Sandstone Properties, Types and Decay Mechanism 4.1 Sandstone Types and Properties 4.2 Sandstone Decay Mechanism 4.2.1 Physical Attack 4.2.2 Chemical Attack 4.2.3 Humans’ Action
16 16 17 17 17 18
5. Condition Survey of the Tron Kirk 5.1 Description of the Tron Kirk Fabric 5.2 Identification of Sandstone Defects on the Tron Kirk 5.2.1 Biological Growth 5.2.2 Loss of Mortar 5.2.3 Crystallization of Salts 5.2.4 Structural Cracks 5.2.5 Spalling/ Erosion 5.2.6 Black Crust 5.2.7 Mineral Soiling 5.2.8 Surface Blistering 5.2.9 Cracks 5.2.10 Vandalism, Graffiti and paints 5.3 The Main Sandstone Defects of the Interior of the Tron Kirk
20 20 26 27 27 28 29 30 30 31 31 32 33 34
6. Conservation Proposal of the Tron Kirk 6.1 Approach of Conservation 6.2 Defects and Repair Strategies
36 36 37
7. List of Figures 8. Bibliography
39 40
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INTRODUCTION
Figure 03: The Tron Kirk north elevation
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1. Introduction: The purpose of this study is to investigate sandstone; to demonstrate an understanding of its properties and different types. Moreover it will review the decay mechanism of this building material through taking the Tron kirk in Edinburgh as a case study. The study will also discuss the conservation techniques required at the Tron Kirk. While a variety of causes of sandstone decay can be outlined, the case study will allow closer examination and analysis of the specific forms of decay evident in that particular context. Furthermore, a conservation approach is to be proposed in regards with these outlines taking into consideration the preservation of authenticity, integrity and stability of the building. The Tron Kirk is one of the oldest churches in Edinburgh and used to be one of the four early parish churches in the city. Situated in the Royal Mile Street, between the castle and the Holy Rood palace as a distinctive historical landmark.
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THE TRON KIRK SITE PROFILE
Figure 04: View of the Tron Kirk from the Royal Mile
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2. The Tron Kirk Site Profile: The Tron Kirk has a square plan with an octogonal steeple presenting clock tower as an outstanding landmarrk in the city of Edinburgh. The design has been alternated several times since the construction in the seventeenth century with Gothic and Classical hybrid styles influence by Dutch architecture. Sandstone is the main building material used for the construction which is seen today as a pale ashlar with fascinating moulded dreesings and obelisk finals.
Figure 05: The Tron Kirk Location, Google Maps
2.1 Site Plan: The Tron Kirk stands in the junction between the Royal Mile street and South Bridge street in Edinburgh old town on one side. On the other side, it’s surrounded by Hunter square which provides an excellent view to the church. The post code of the building is EH1 1HN on High street, Edinburgh. 2.2 Vital Statistics: The Tron Kirk was closed as a place for worship in 1952 and the ownership of the building belongs to Edinburgh City Council. Local Planners used the building as a visitor centre for the Edinburgh World Heritage Site in 2003 and now it’s been closed waiting a long-term plan for using the building by the City Council. The building is included in the conservation area as an A listed building and categorized under buildings at moderate risk. In 2008, inspections found that the church is generally in good condition, but with deterioration evident to the windows and some damage to the lower stones by the High Street entrance. The building is currently vacant awaiting the implementation of refurbishment and reuse.
Figure 06: Street Map of Edinburgh World Heritage Site and Surrounding Areas, Gaurdian News and Media
Figure 07:: The Tron Kirk Location on Edinburgh Map
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Brief Historical Description of the Tron Kirk
Figure 08: Edinburgh Tron Kirk New Years Eve, Tour Scotland website.
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3. Brief Historical Desciption of the Tron Kirk : 3.1 Early Construction of the Tron Kirk 17th Century ;
The Tron Kirk is believed to be one of the oldest churches in Edinburgh and used to be one of the four early parish churches in the city. it was ordered to be built by King Charles I when he created Edinburgh as a city and changed the nearby St Giles from a church into a cathedral in 1636. The design was done by John Mylne after demolishing multi-storey buildings on the site. The Design in characterised by a hybrid Gothic and Classical Styles with a Dutch influence.1
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Figure 09: James Gordon, Map of Edinburgh 1647, The National Library of Scotland
The roof which is designed by John Scott wasn’t completed until 1663. The Hummer beam roof was similar to the parliament hall’s roof designed by the same architect.
Figure 10: Engraving of the kirk as it looked before 1785, Wikimedia Foundation
Figure 11: John Elphinstone, A Perespective View of the Front of the Tron Kirk. RCHAMS
1. Deborah Architecture of Scotland: Reformation to Restoration, 1560-1660 Edinburgh University Press, 1995, p.192
3.2 Later Alternations in the 18th and 19th Centuries :
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In 1785, the construction of the South Bridge altered the Tron Kirk original T-shape plan to a square plan by shortening the south and the east aisles of the church. The western edge of the kirk removed in order to restore symmetry. The alternation of the design was done by the architect John Baxter who did some changes in both interior and exterior of the building to accommodate the South Bridge and Hunter Square.2 
Figure 12: A view to the Tron Kirk and Hunter Square, Scanned image of engraving. RCHAMS
The Edinburgh old town fire that took place in 1842 destroyed the original timber steeple of the Tron Kirk which was added by Thomas Sandilands in 1671 and caused some damages to the building. The Steeple had an exceptional significance to be largely influenced by a Dutch style and to be made of timber and lead. Afterwards, R&R Dickson architects designed a new higher tower, which was constructed in 1828 and was entirely constructed by stone presumably to prevent it from falling victim to fire ever again.3
Figure 13: The Great Fire of Edinburgh 1824, The former steeple of the Tron Kirk is appeared in fire. The Scotsman 2. Mclean, D. Lost Edinburgh: The Tron Kirk. 03 June 2013, the Scotsman. 3. Ibid.
12 By then, the church started to be more important and it was the place to held the general assembly of the Church of Scotland. In 1884 James Ballantine & son installed stained glass windows in west and east walls of the Tron Kirk. 3.3 Modern History of the Tron Kirk (20th - 21st Centuries): The Church was closed for worship in 1952 and remained unused for many years. Excavations within the church in 1974 uncovered the remains of Marlin’s Wynd, including cellars and what is thought to be the oldest surviving paved street in Edinburgh in the restoration project.4
The conservation proposition was done by Simpson and Brown architects that suggested rebuilding parts of the Hammer beam roof that had been damaged in the 1842 fire and was severely rooted. The Scheme suggested restoring the stone work by taking off the pieces that have scale and deposits, it also adding new stone pieces as the original elements. Moreover, it proposed to inject the walls affected by dry with fungicidal fluid. A scheme for reusing the interior was proposed but not undertaken. The recent November 2006–December 2007 works re-exposed previously identified remains associated with the 17th-century tenements and previously unknown cellars and buildings dating to the same period. The fragmentary remains of an early phase of the Royal Mile were exposed as well as the remains of five tenement buildings, including in situ floor remains and an area of probable industrial processing. The artefact assemblage consisted of material relating to the post-medieval Figure 14: The Tron Kirk after the construction of the New Steeple 1829. Modern Athens
Figure 15: Arial view of Centre of Edinburgh. The Tron Kirk in Highlighted. RCAHMS 4. The Tron Kirk, Edinburgh Evening News, 8 Mar 2004, p.9 and 20 Dec 2004, p.21 5.Binney and Burman (1977a) Change and decay: the future of our churches, Edinburgh College of Art library. P. 44
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Figure 16: Interior general view from North-East During Excavations. RCAHMS
Conservation History Timeline: 1647 -Construction of the Tron Kirk by John Mylne using local sandstone which was brought from Craigleith quarry and Society quarry. 6 1678 - Clock from the Butter Tron (destroyed by Cromwell 1652) installed in the steeple. 1785 - Building of South Bridge and Hunter Square; alterations to exterior and interior by architect John Baxter. The sandstone used in the alternation was brought from Craigleith quarry.7 1824 - Fire destroys steeple. 1828- R&R Dickson architects designed a new higher tower, which was constructed by Humbie quarry sandstone.8 1830 - General Assembly of the Church of Scotland held at the Tron 1884 - Commemorative stained glass windows installed in west and east wall, by James Ballantine & Son 1952 - Congregation ceases to use Tron; building closed for worship 1953 - Negotiations involving Secretary of State for Scotland and Edinburgh Corporation over future of Tron 1972 - Secretary of State conveys Tron Kirk to Edinburgh Corporation, with condition of some public access to the building 1974 - Major repairs to masonry using Darney quarry sandstone 9, steeple, roof and archaeological investigation of area below floor level 1993 2006 - Tron leased as Old Town Information Centre, open in the summer with temporary walkway for viewing archaeological remains. 6. A. A. McMillan, R. J. Gillanders & J. A. Fairhurst (1997). Building Stones of Edinburgh. British Geological Survey Archive. P8 7. A. A. McMillan, R. J. Gillanders & J. A. Fairhurst (1997). Building Stones of Edinburgh. British Geological Survey Archive. P9 8. Ibid 9. Ibid
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Figure 17: Gallery Plan; Ground Floor Plan (incorporating excavations). RCAHMS
Figure 18: Humbie Quarry, Scotland. Bikelove Scotland website
Figure 19: Thomas. (1850) Craigleith Quarry, Scotland. Ssplprints
Figure 20: Darney Quarry, Scotland. Geograph UK website
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Sandstone Properties, Types and Decay Mechanism
Figure 21: Sandstone. Hard Landscape and Gardens website.
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4. Sandstone Properties, Types and Decay Mehanism: Rocks are classified into three geological types: Igneous, Sedimentary and Metamorphic. Sandstone is a sedimentary rock formed by layers of visible minerals grain constituents held together by a natural cement matrix. Scotland is well-known in using sandstone as a building material. It’s likely that the sandstone used in the construction and repairs of the Tron Kirk came from Craigleith, Society, Humbie and Darney quarries . 10 The strength of the stone is known by the strength of the binding agent. The composition of the grains reflects the physical and chemical resistance to the weathering of the stone. The binders found in the sandstone are Silica, Calcite, clay minerals and iron oxide which are responsible for the texture and the colour of the stone. 11 There are many types of sandstone which are different in colour and durability. This variation might come from the materials between particles, age of the stone and its compacting level.
Figure 22: Thin section seen under microscope of medium grained sandstone. The sand grains are clear and the brown material imbetween the grains is carbonate cement. Maher 2010
4.1 Sandstone types and properties: Depending on the sandstone’s grains, which form the whole structure of the stone beds, we can identify the type of sandstone as well as the main differences between them. Sandstone mainly consists of quartz and some other minerals. Thus, a lot of sandstone types were formed because of the difference in percentages of sand and other grains in the stone structure. Besides, the second constituent plays the basic role in defining the sandstone type, its chemical stability as well as cementing properties. According to Forsyth12, Sandstone types could be classified into the following: 1- Agrillaceous Sandstone: in this type, clay plays the subsidiary constituent role. For that this type has a weak resistance to the environmental issues especially wet weather. This weakness is as a result of the clay bad performance in water. 2- Calcareous Sandstone: this type has good cementing properties because of the main constituent material which is calcite (CaCO3) or calcium carbonate as it is known. Unfortunately, it has a bad performance to acid pollution because calcium is easily affected by atmospheric acids especially the carbon dioxide. 3- Dolomitic Sandstone: the main constituent material in this type is Dolomitic which has this formula [Ca Mg (CO3)4]. Due to the presence of calcium and magnesium, this type is described with good cementing properties. But it is, like calcareous sandstone, extremely affected by acid pollution. 10. Trewin, N. H. (2002). The Geology of Scotland. British Geological Survey archive. p.465 11. Heathcote, L. (1998-99). Sandstone: Its properties, Application and Conservation Edinburgh. Edinburgh College of Art archive. P. 122 12. Forsyth, M. (2008). Materials amd Skills for Historic Building Conservation Edinburgh Blackwell publishing LTD.
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4- Ferruginous Sandstone: the basic cementing materials in this type are oxides of iron. These oxides give this type the red colour as well as good cementing properties. The weathering of this type will increase as a result of the presence of other less stable constituents. 5- Siliceous Sandstone: this type has the best weathering properties because either water or atmospheric gases pollution cannot affect it. This good resistance comes from Silica which plays the dominant cementing material. 4.2 Sandstone Decay Mechanism:
Once sandstone is removed from its position in the quarry and placed in a building, its sedimentary formation makes it vulnerable to a variety of potential decay mechanisms of both physical and chemical origin. The causes of decay are resulted from natural factors as well as human interference and activities. 4.2.1 Physical Attack: Physical weathering causes disintegration of the stone without altering the chemical composition. Water entering the pores of the stone is normally removed by the evaporation of the surface in the cycle of wetting and drying. The damage is caused when the minerals in the stone change their sizes by absorbing and releasing water. The expansion of these minerals adds pressure on some parts and results in pushing them out of the composition. Frost also affects the integration of stone components and cause disruption. After the water changes its status from liquid to ice, the particles of the water expand and cause disruption. 13 Natural factors of decay also include the effects of sun and wind. Some particles and rainwater are carried by wind into the stone and the wind could also carry away some other particles from the stone and cause erosion.14 The temperature of the minerals differs between day and night and in some cases the alternation could cause expansion and contraction of minerals. Moreover sandstone could be vulnerable to salt attack in some coastal climates that causes disintegration of stone particles. For example after water evaporation, some materials deposited in the water can crystallise and disrupt the sandstone matrix observed as efflorescence in stone. 4.2.2 Chemical Attack: Chemical weathering refers to alternation and dissolution of some of the sandstones constituent elements. Particles are washed off or leached by rainwater, atmospheric pollution which causes soiling, or by-products of biological growths. The pollution gases which have been produced in the atmosphere are harmful to the structure of sandstone. The calcareous sandstone is affected by carbon dioxide and acid sulphur gases. These gases create a layer of salt on the outside surface of the stone. Thus, when the sandstone is washing up by rainwater, water and salt go to the non-calcareous sandstone and lead to a crystallization damage. Biological growth is one of the significant factors which affect sandstone. The algae growth and its extension inside the mortar allow moisture to take place inside walls. These spaces give an opportunity for water, salt, and acid to enter the building’s walls. Therefore, they affect the sandstone as well as the building structure. Bird droppings can increase the possibility of the biological growth since they contain nutrients that encourage the biological growth as well as causing soiling.15
13. Heathcote, L. (1998-99). Sandstone: Its Properties, Application and Conservation Edinburgh. Edinburgh College of Art archive. P. 89 14. Forsyth, M. (2008). Materials amd Skills for Historic Building Conservation Edinburgh Blackwell publishing LTD. 15. Ibid
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4.2.3 Humans’ Actions: The man plats a major role in stone decay from the early stage of removing it from its original setting and subsequently exposing it to external perishing forces. The way sandstone is incorporated into a building is crucial in affecting its ability to withstand the various effects. The bedding process of the sandstone in quarries during the deposition and progressive existing of the geological layer are mainly responsible for the sandstone delamination. Face bedded is the most potential case which causes delamination in sandstone. However, in spite of the correct bedding for the rocks in nature, sandstone will suffer from this problem because of its natural structure. In addition, there are many physical attacks happen to the sandstone because of either natural factors or human behaviour. All these factors sometimes lead to fail structure problem because of the decrease in sandstone resistance which happens differently regarding to one or more stone defects.
Furthermore, using certain material and techniques in sandstone repairs could cause the decay as well. Some of the materials used in the restoration schemes could not incorporate well with the original materials and cause damage to the original one. For example, using cement as a mortar could harm the sandstone in longterm period. Cement is a harder, less porous material than sandstone. When pointing or plastic repairs are completed in this, it can lead to coving and erosion of the sandstone as salts in the concrete leach out via water and damage the surrounding stonework. Its lack of flexibility as a mortar compared to lime means it doesn’t allow differential movements and consequently cracks can develop in the weaker stone instead. 16 Inappropriate cleaning methods can also damage the stone when harsh chemicals and treatments are utilized result in erosion, staining, discolouration, bleaching and loss of detail. However, neglecting routine maintenance to the stone-work could permit problems to develop in some cases.
16. Heathcote, L. (1998-99). Sandstone: Its Properties, Application and Conservation Edinburgh. Edinburgh College of Art archive. P. 90
Condition Survey of the Tron Kirk:
Figure 23: Sandstone decay of the column inside the Tron Kirk
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5. Condition Survey of the Tron Kirk:
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After the church stopped to serve as a place for worship in 1952, it was abandoned for a long time and left to decay. Therefore, the building was subjected to weathering and had no routine maintenance for a long period. The first maintenance project was undertaken in 1974 that included cleaning, repointing and replacement to some elements including stone, timber beams, slate and glass panels as well as structural consolidation in certain areas.
Figure 24: Broken and missing galss panels in the East elevation.
Figure 25: Glass replacement with sandstone in the South elevation.
Figure 26: Depositis on the roof, South elevation.
figure 27: Algae growth on the roof, North elevation.
5.1 Description of the Tron Kirk Fabric : The site was visited and surveyed during March 2014. The survey included photographs, some measurements and historical information such as texts and pictures. As a result, the church was found in relatively good condition with some problems to be discussed in the report. The church is mainly built by sandstone brought from different quarries in different periods. Moreover, the church was subjected to several alternation since the date of its construction in 1647. Thus, the usage of different sandstone types with a several changes in the form of the building could be two of the main causes of the sandstone decay.
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The roof is finished by slate which is relatively in a good condition as well with some problems. The main problems of the roof are algae growth that is clearly noticeable in the North elevation and salt efflorescence in the south elevation. However, the slate pieced are tight and complete due the fact that the roof was restored in 1974 and many slate pieces were replaced and other were cleaned.
Another main building material of the exterior of the Tron Kirk is the glass. Apparently, some parts of the glass in the windows have been removed and replaced with sandstone (south elevation) and others with double glazed clear panels (west elevatin), while other parts seems to be missing (north, west and east elevations).
Figure 28: Hummer beam roof of the Tron Kirk designed by John Scott in 1663.
Moving to the interior part of the building, the hummer beam roof which is one of the unique features of the church is suffering from wet rot, dry rot and limited areas of beetle attack. Many beams were replaced and others were repaired during the conservation scheme in 1974. In addition, There are extensive areas of poor quality cement mortar patching on the walls of the interior which dates back to the 1950s repairs . The study will focus on sandstone condition in the exterior of the Tron Kirk as well as highlighting some of the observed defects in the interior due the fact that the report should have a limited word count.
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Figure 29: Major illustrations to the sandstone decay in the Tron Kirk north elevation
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Figure 30: Major illustrations to the sandstone decay in the Tron Kirk south elevation
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Figure 31: Major illustrations to the sandstone decay in the Tron Kirk east elevation
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Figure 32: Major illustrations to the sandstone decay in the Tron Kirk west elevation
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5.2 Identification of Sandstone Defects on the Tron Kirk:
Sandstone is the main building material used in the Tron Kirk. Sandstone is used in the arches, decorative elements and columns. Moreover, sandstone ashlar blocks were used to construct the walls of the building. The sandstone used in the Tron Kirk suffers from a variety of problems that could be classified as major and minor problems according to the damage they cause and the damage that might cause in the future. The major problems of the sandstone used in the exterior of the Tron Kirk are biological growth, structural cracks, crystallization of salts, spalling, loss of mortar details in masonry. While the minor problems of the sandstone used in the exterior of the Tron Kirk are graffiti, paints, vandalism, blistering and stained stone including mineral soiling as well as dark and normal black stains. 5.2.1 Biological Growth: The colonisation of building sandstones by biological growths is investigated in terms of their dependence on certain physical and chemical parameters of sandstones including the supply of nutrients, surface roughness and moisture availability. 17 Algae and Moses growth as well as vegetation are the types of the biological growth found as sandstone defects in the Tron Kirk. Algae growth is particularly intense in the northern side of the church and could be clearly seen on the watershed elements, moist places and behind the water pipes. The causes might be the availability of the moisture and rainwater flow as well as roughness of some stone surfaces. Mosses growth is found on the four sides of the building. However, it’s more likely to be found on west and east elevations than the other sides, probably because of the sunlight exposure. Vegetation or plant growth is also found in some parts of the building where there is often cracks or gaps in the stone. The plants usually need moisture, nutrients, sun and some sort of soiling to grow and they often cause a serious damage to the stonework by keeping the moisture inside as well as causing cracks by the growth of their roots. Biological growths are capable of causing disfigurement and damage to building stone, therefore in some cases their presence may be considered undesirable, especially where the stone is exposed to rainfall or conditions of high humidity, since biological growths are most active under such conditions. Many organisms secrete acids and other substances as a result of their metabolic processes which may affect rock-forming minerals and can be destructive to stone.18 Growths can obscure and cause deterioration of inscriptions and carvings and some may stain walls. Biological growth can trap dirt and pollutants, leading to accelerated soiling of a building surface and aiding the establishment of higher plants which increase water retention and may lead to blockages of gutters and downpipes.19
Figure 33: Vegetation on south elevation
Figure 34: Mosses growth on the west elevation
17. Wainwrite, M (1986). Lichen removal from an engraved memorial to Walt Whitman. Association for Preservation Technology Bulletin. P46 18. Ibid 19. Seaward, M.R.D (1979). Lower plants and the urban landscape, Urban Ecology. P217-P219
Figure 35: Algae growth on the north elevation
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5.2.2 Loss of Mortar:
Figure 36: Loss of mortar in the east elevation
Figure 37: Loss of mortar in the North
Generally Ashlar masonry walls work on the basis that moisture entering a wall is able to escape as water and water vapour as easily as possible. Lime mortars can readily handle the transmission of water and water vapour between the inside and outside of a masonry wall, owing to the complex interconnected pore structure of masonry. 20 The original mortar which is lime mortar in most of the cases of the exterior part of the church, has decayed over time and needs to be replaced. This may be the result of gradual decay through weathering, or failure as a result of poor maintenance. Blocked gutters or overflow pipes, for example, lead to damp masonry. The issue is mostly found on the north elevation of the Tron Kirk, where is believed to be the highest exposure to moisture and salt. The lack of the mortar is making an aesthetic problem and could make a serious structural problem as well as threatening the stone blocks to have more decay since nothing is protecting them from the flow of water. 5.2.3 Crystallization of Salts: Efflorescence is a crystaline deposit on surfaces of masonry.They are water-soluble salts that come from many possible sources to mar and detract from the structure. First of all, there must be water present to dissolve and transport the salts. Groundwater is often a source of efflorescence. For water to carry or move the salts to the surface there must be channels through which to move and migrate. The more dense the material, the more difficult for the water to transport salts to the surface. 21
Figure 38: Salt Effloresence on west elevation
Figure 39: Salt Effloresence on west elevation
Conversely, the more porous the material, the greater the ease with which salts are transported and deposited. Salt-bearing water, on reaching the surface of a structure, air evaporates to deposit the salt.22 The salt deposits are found on all of the Tron Kirk elevations, particularly on the lower part of the building where more damp are probably transferred from the groundwater. 20. Gibbons, P. (1995) Scottish Lime Centre Trust, Historic Scotland Technical Advice Note 1, Preparation and Use of Lime Mortars, Historic Scotland P 34 21 Cement. K (2001) Efflorescence: Causes, Removal, and Prevention. Graniterock website. Accssed on 27 April 2014. 22. Ibid
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5.2.4 Structural Cracks:
Traces of structural cracks could be noticed on both west and east elevations of the Tron Krik indicating the movement of the structure. The cracks have diagonal paths on the centre of both elevations and a little bit longer on the east elevation of the church. According to the article, Structural Movement, written by Clive Richardson in building conservation website: “New structures are designed to carry their own weight and imposed loads so that strains are kept within reasonable limits; safety factors are included to cater for variations in quality of materials, design and construction inaccuracies, and random or accidental forces. In historic structures det rimental movement results from inadequate design and construction, decay and ill-considered alterations.�23
Figure 40: Structural Cracks on east elevation
Therefore, the structural cracks could be a result of variety of reasons. The first one might be the inadequate design and construction since there have been many alternation to the structure since its construction in the 17th century. For instance. the west and east sides of the church have been shortened and alternated to integrate with the rest of the building fabric during the construction of the South Bridge and Hunter Square in the 18th century. Furthermore, different alternations took place in different parts of the structure afterwards. Another reason might be the sandstone decay problems in which the building is suffering from. The third reason might be the heavy traffic vibration, especially on the eastern part of the church where the most crowded street is located. 23. Richardson, C. (1996). Structural Movement. The Building Conservation Directory. Website. Accessed on 27 April 2014.
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Figure 41: Structural Cracks on west elevation
5.2.5 Spalling/ Erosion: Through wetting and drying cycle of the surface of a sandstone wall over the years, more of the exposed stone surfaces begin to gradually erode a little. This is natural weathering. Extremely wet weather with unusually low temperatures heightens the natural weathering. The atmospheric pollutant, sulphur dioxide, combines with the calcium carbonate in the sandstone and creates a hard gypsum layer covering the surface of the stone.24 This means that moisture inside the stone cannot escape and salts may crystallize behind this hard layer and eventually cause spalling, which leaves a weak exposed surface, more vulnerable to natural weathering. Spalling and other types of stone decay are more noticeable on the lower sides of the Tron Kirk elevations, probably because the lower parts suffer from more salt crystallization and water penetration issues.
Figure 42: Structural Cracks on west elevation
Figure 43: Structural Cracks on west elevation
24. Rossi-Manaresi et al, (1995) Long-term Effectiveness of Treatments of Sandstone', ICCROM International Colloquium on methods of evaluating products for the conservation of porous building materials in monuments. British Geological Survey Archive, Edinburgh. P21
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5.2.6 Black Crust (Black Stains):
The exterior of the Tron Kirk suffers from the development of black crust on the surface of the stonework. The black crust, also known as black stains, on the surfaces of the sandstone are classified into two types: dark black crust and normal black crust. The dark black crust has probably developed earlier than the normal black crust found on the exterior of the Tron Kirk. The development of these staines could be due the deposition of some of pollutant particulates in the atmosphere known as soot which are probably the cause of the existence of the dark black crust on north and east elevations of the church that are exposed to heavy traffic and consequently more smoke and pollutant deposits. However, the formation of the black crust could be due but the reaction of sulfur dioxide and calcium carbonate that may be present. Sulphur dioxide reacts with water in the atmosphere to produce sulphurous acid (H2SO3) which could be deposited on the surface of the sandstone by the reaction with the calcium carbonate causing the formation of the black crust. 25
Figure 44: example of normal back crust on the north side of the
Figure 45: example of dark back crust on the west elevation
5.2.7 Mineral Soiling: Mineral soiling is another form of soiling that could be seen on the surface of the stone. Sandstone is relatively porous and permeable. Liquids can therefore move through most sandstone with considerable ease. As the moisture evaporates from the stone, this fluid, containing materials dissolved from within the stone, is drawn towards the surface where it evaporates depositing any soluble material. Such movement of materials from within the sandstone can result in staining at the stone’s surface and mineralogical changes.26 The high number of the sandstone blocks that have been stained by minerals on the south elevation of the Tron Kirk indicates the movement of the minerals within the stone blocks in the building. These minerals could be driven by the liquids flowing within the stone which are mainly rainfall water. The more the stone losses its minerals the more weaker and vulnerable to decay it becomes.
Figure 46: Mineral Soiling, South Elevation
Figure 47: Mineral Soiling on the South Elevation
25. Brimblecombe, P. (2004). The effects of air pollution on the built environment, Imperial College Press. The British Geological Survey archive, Edinburgh 2014. P23 26. Rossi-Manaresi et al, (1995) Long-term Effectiveness of Treatments of Sandstone', ICCROM International Colloquium on methods of evaluating products for the conservation of porous building materials in monuments. British Geological Survey Archive, Edinburgh. P22
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5.2.8 Surface Blistering:
Sandstone blistering is a swelling on the surface followed by a rupturing of a thin, uniform skin. A blister forms in the surface layers of the stone, in the few outer millimeters. Blisters are characterized by a bowing or lifted surface.27 It is typically caused by deicing salts and/or ground water, therefore it is usually localized near ground level where there is a coexistent exposure to sunlight and found on the lower part of the Tron Kirk, especially on the northern side of the church. The blisters could be harmful to the sandstone and could develop by time causing a material loss.
Figure 48: Surface blistering, north elevation
Figure 49: Surface blistering, north elevation
5.2.9 Cracks: There are a number of metal fixtures used in the exterior of the Tron Kirk and apparently caused cracks within the stone which they are inserted. The cracks happen due the expansion of the steel as it rusts generates a force sufficient to cause cracking and sometimes dislocation of stone elements which is clearly observed in this case study. These cracks could result in breaking of the stone blocks from within as well as detaching the broken parts and consequently present a serious threat to the building.
Figure 50: Cracks caused by metal fixures, west elevation
27. Pitting, Flaking & Blistering, Modes of Stone Decay article. Info Tile website. Accessed on 21 April 2014
Figure 51: Cracks caused by metal fixures, east elevation
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5.2.10 Vandalism, Graffiti and paints:
Graffiti is a common phenomena found in Edinburgh, especially in those structures which are abandoned. The Tron Kirk is still an abandoned place located in a central area of the city, which is potentially a desirable site for the graffitists. Graffiti and other forms of paints attached to the stonework affect the aesthetics of the historic building. In addition, painting over a deteriorated stone surface may lead to more serious moisture-related problems when necessary treatment is deferred.
Figure 52: Grafitti, west elevation
Figure 53: Grafitti, north elevation
In addition to the graffiti works, there are a number of casual vandalism practices in the stonework. For example, papers and other trash are found in some stone gaps where mortar or stone fragment should exist.
Figure 54: Vandalism, south elevation
Figure 55: Paints, west elevation
5.3 The Main Sandstone Defects of the Interior of the Tron Kirk:
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As mentioned earlier in the report, the study will focus on the condition of the exterior of the Tron Kirk rather than focusing on the interior due the fact that the length of the report should be limited to a certain number of words. Therefore some of the defects and problems will be only highlighted in the following paragraphs.
Figure 56: Interior view of the Tron Kirk
The interior part of the Tron Kirk suffers from a relatively more defects than the exterior part of the church because the interior has been left abandoned for many years until the use of it by the city council for the hegemony parties and other concerts recently. Moreover, the archeological works to discover the traces of the medieval tenements have prevented the intervention of some instant conservation works in the building. The main defect of the sandstone in the interior of the Tron Kirk are the cement pointing, structural cracks, loss of masonry elements and details, stone trim, brick and stone replacement and soiling including mineral and black stains as well as salt deposits. Some of these problems could be the cause of manifestations of defects on the exterior part of the church and could intrinsically linked with the sandstone decay problems of the exterior facades. Huge parts of the interior facades are pointed with cement during the conservation works that took place in the 20th century. Apparently, the cement mortar has created serious problems to the masonry causing scaling and spalling issues to the stonework inside the church. Since the cement mortar is harder than the sandstone, it is more likely for the water to flow inside the stone than to flow in the cement mortar and this might be one of the main causes of many defects in the exterior parts of the church. There is also some other indications of structural cracks in the church interior masonry. The cracks have diagonal paths similar to the ones observed in the exterior and could be another indication of the movement of the structure. These cracks could make a serious problem to the stability and integrity of the structure and require a structural engineer for further investigations.
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Figure 44: Decay in stone caused by cement pointing
Figure 57: Loss of masonry details
Figure 59: Stone replacement of missing parts
Figure 61: Sandstone soiling
Figure 45: Decay in stone caused by cement pointing
Figure 58: Loss of masonry elements
Figure 60: Brick replacement of missing parts
Figure 62: Structural cracks
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Conservation proposal for the Tron Kirk:
Figure 63: South view of the Tron Kirk Steeple
6
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6. Conservation proposal for the Tron Kirk: 6.1 Approach of Conservation: The Tron Kirk is a building of immense importance from an historical and architectural point of view, as well as being a landmark and notional halfway point on Edinburgh’s Royal Mile. After being the centre of Edinburgh’s Hogmanay, the building has struggled in recent years to find a role in keeping with the significance and prominence of its location and architectural quality. Therefore the Edinburgh City Council decided to make a development scheme for the Tron Kirk to be converted to provide an interactive visitor centre on the ground floor with provision for a cafe / restaurant on a new mezzanine floor. Since then, a number of development schemes for the building have been proposed by different architects but none of them was undertaken. It’s important for any development scheme to provide a conservation plan to preserve the architectural, historical and archeological significance of the Tron Kirk and ensure the continuity of this significance to pass to the future generations. The conservation plan must preserve the original fabric of the building to the utmost. According to the Baurra Charter “ Preservation is the action taken to maintain the fabric of a place in its existing state and to anticipate, prevent, stop, or slow deterioration “. 28 In order to make an integral conservation plan to the Tron Kirk sandstone, the decay problems of the sandstone must be prioritized according to the urgency and threat on the building. For this reason, problems are classified into three categories (minimal, moderate and major problems) according to their urgency. Minimal problems require desirable preservation intervention, while moderate ones require a necessary preservation intervention, and finally, major ones require an immediate preservation intervention. Any proposed material or technique for the conservation plan should be chosen carefully to ensure the durability of the action in regards to the preservation of the original materials. For example, the conservation proposal must use lime mortar for the repointing of the sandstone masonry and not using cement or other plastic mortars because of the defects they might cause in the long term. In addition, the ssandstone that is supposed to be used for replacement should be chosen according to its colour and properties to interact well with the original sandstone fabric and preferred to be obtained from the same quarries of the original sandstone materials if possible.
28. The Burra Charter: (2013) The Australia ICOMOS Charter for Places of Cultural Significance. Australia ICOMOS website. Accessed on 27 April 2014
37 6.2 Defects and Repair Strategies: Decay Biological Growth (Algae and Moss Growoth) Biological Growth (Vegetation) Loss of Mortar
Crystallization of Salts
Spalling/ Erosion
Structural Cracks
Desciption Algae and mosses growth exist in different parts of the building exterior, especially on the north facade where the building is largely exposed to moisture.
Treatement Urgency Flashing should be inserted on the infected Necessary areas of the building. The flashing should have a minimal impact on the masonry and should result in a colour that matches the stonework. The drainage system of the building must be checked and downpipes and gutters should be cleaned and fixed if broken. Grown plants are mainly found The plants should be removed from the Necessary in the south elevation where building and replaced with appropriate matethe suitable condition are rials to infill the gaps caused by the plants. available. Different parts of the church Where joints have failed, they should be filled Immediate have a lack of mortar that and repointed by a lime based mortar. The could cause serious problems mortar should also replace the cement joints in the future. The areas in used in the building where the mortar could which the mortar is lost are be removed, however the removal should mainly located on the lower prevent the detonation of sandstone by the part of the building. process though checking the status of the cement mortar and the stone The salt deposits are found on Reducing the amount of salt crystallization Desirable all of the Tron Kirk elevations, happens when the building gets more dry. particularly on the lower part Increasing the dryness is achieved by improvof the building where more ing the drainage system of the building and damp are probably transferred repointing the joints where the water might from the ground water. flow, especially on the lower level. Spalling and other types of The spalling and other decay issues of the Necessary stone decay is more noticesandstone should be addressed by replacing able on the lower sides of the the stones that have a large areas of scaling Tron Kirk elevations, probably with new sandstones according to their because the lower parts suffer colour and properties to interact well with from more salt crystallization the original sandstone fabric and preferred and water penetration issues. to be obtained from the same quarries of the original sandstone materials if possible. However, the stonework that suffers from a normal scaling should be cleaning by clearing the loose edges with a brush and desalinate the affected area. Traces of diagonal structural Traces of diagonal structural cracks could be Immediate cracks could be noticed on noticed on both west and east elevations of both west and east elevations the Tron Kirk indicating the movement of the of the Tron Kirk indicating the structure. These cracks could make a serious movement of the structure. problem to the stability and integrity of the These cracks could make a structure serious problem to the stability and integrity of the structure
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Decay Dark Black Crust (Black Stain)
Desciption the exterior part of the Tron Kirk suffers from the development of dark black crust, especially on the north elevation.
Treatement Cleaning the stone is not necessary in this case. The best practice would be keeping the stone as dry as possible by improving the drainage of the building as well as infilling the joints with appropriate mortar. Normal Black Normal black crust is found in Cleaning the stone is not necessary in this Crust (Black different areas of the church, case. The best practice is to keep the stone as Stain) especially on the spire and west it is. elevation. Mineral The mineral soiling exists in Cleaning the stone is not necessary in this Soiling different parts of the church case. The best practice would be keeping the and densely found on the stone as dry as possible by improving the south elevation of the building. drainage of the building as well as infilling the joints with appropriate mortar. Surface Sandstone surface blistering The development of blistering should be Blistering is mostly located on the lower monitored and the stones which suffer from part of the Tron Kirk, near the blistered surfaces should be desalinated, ground level where there is a cleaned and dried sensitively. coexistent exposure to sunlight, especially on the northern side of the church. Cracks There are a number of metal The best practice is to keep monitoring fixtures used in the exterior of the development of the cracks caused by the Tron Kirk and apparently the expansion of the metal fixtures that are caused cracks within the stone inserted deeply in the stone and to removed which they are inserte the shallow inserted metal fixtures and fill the gap with lime based mortar. It’s also necessary to replace the stone blocks that are highly damaged. Graffiti and Graffiti and paint works are Undesirable graffiti and paints works could Paints found on the exterior masonry be removed from the sandstone by using speof the Tron Kirk. cial chemicals sensitively. Choosing the write technique and substances is very important to make as less damage to the surface of the stone as possible. However, it's recommended to keep the graffiti and paint works without an action if they don't make a considerable problem.
Urgency Desirable
No Action
Desirable
Desirable
Necessary
Desirable
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7. Lists of Figures: Unless otherwise specified, all drawings are photographs are produced by the author. Figure 05: The Tron Kirk Location, Edited by the author, Google Maps. Accessed on 18 April 2014 : https:// www.google.co.uk/maps/@55.9495839,-3.1574108,14z Figure 06: Street Map of Edinburgh World Heritage Site and Surrounding Areas, Guardian News and Media. Accessed on 20 April 2014 : http://www.theguardian.com/edinburgh/2011/mar/08/edinburgh-sutherland-hussey-shed-stockbridge Figure 07: The Tron Kirk Location on Edinburgh Map, Wikimedia Foundation. Accessed on 20 April 2014: http://www.google.co.uk/imgres?imgurl=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fc%2Fcc%2FEdinburgh_UK_location_map.svg&imgrefurl=http%3A%2F%2Fen.wikipedia. org%2Fwiki%2FEdinburgh_Airport&h=1384&w=1330&tbnid=EbwjU3quDExFDM%3A&zoom=1&docid=rg8TUUgqFbvhzM&ei=6-tUU5GrBoKdO_TkgaAC&tbm=isch&ved=0CKUBEDMoMDAw&iact=rc&u act=3&dur=328&page=3&start=31&ndsp=20 Figure 08: Edinburgh Tron Kirk New Years Eve, Tour Scotland website. Accessed on 14 March 2014: http:// tour-scotland.blogspot.co.uk/2007_12_01_archive.html Figure 09: Gordon, J. Map of Edinburgh 1647, The National Library of Scotland website. Accessed on19 April: http://maps.nls.uk/towns/detail.cfm?id=211 Figure 10: Engraving of the Kirk as it Looked before 1785, Wikimedia Foundation Figure 11: Elphinstone, J. A Perespective View of the Front of the Tron Kirk. RCHAMS, Accessed on 15 March 2014 http://canmore.rcahms.gov.uk/en/site/52236/details/edinburgh+high+street+tron+church/ Figure 12: A view to the Tron Kirk and Hunter Square, Scanned image of engraving. Royal Commission on the Ancient and Historic Monuments of Scotland. Accessed on 14 March 2014 : http://canmore.rcahms.gov. uk/en/site/52236/details/edinburgh+high+street+tron+church/ Figure 13: The Great Fire of Edinburgh 1824, The former steeple of the Tron Kirk is appeared in fire. The Scotsman. Accessed on 24 March 2014 : http://www.scotsman.com/lifestyle/heritage/lost-edinburgh-thegreat-fire-of-edinburgh-1-3029833 Figure 14: The Tron Kirk after the construction of the New Steeple 1829. Engraving from Modern Athens website. Accessed on 24 March 2014 : http://www.edinphoto.org.uk/0_eng/0_engraving_-_ma_009-a_tron_ kirk_col.htm#engraving Figure 15: Arial view of Centre of Edinburgh, the Tron Kirk is highlighted. Royal Commission on the Ancient and Historic Monuments of Scotland website. Accessed on 14 March 2014: http://canmore.rcahms.gov. uk/en/details/421976/ Figure 16: Interior general view from North-East During Excavations. Royal Commission on the Ancient and Historic Monuments of Scotland. Accessed on 14 March 2014 : http://canmore.rcahms.gov.uk/en/site/52236/ details/edinburgh+high+street+tron+church/ Figure 17: Gallery Plan; Ground Floor Plan (incorporating excavations). Royal Commission on the Ancient and Historic Monuments of Scotland. Accessed on 14 March 2014 : http://canmore.rcahms.gov.uk/en/ site/52236/details/gallery+pan/ Figure 18: Humbie Quarry, Scotland. Bikelove Scotland website. Accessed on 23 April 2014: http://bikelove-scotland.blogspot.co.uk/2012/05/crichton-castle.html Figure 19: Thomas. (1850) Craigleith Quarry, Scotland. Ssplprints website. Accessed on 23 April: http:// www.ssplprints.com/image/108450/picken-thomas-craigleith-quarry-edinburgh-c-1850s
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8. Bibliography: A. A. McMillan, R. J. Gillanders & J. A. Fairhurst (1997). Building Stones of Edinburgh. British Geological Survey Archive. P (8-9) Binney and Burman (1977a) Change and decay: the future of our churches, Edinburgh College of Art library. P. 44 Brimblecombe, P. (2004). The effects of air pollution on the built environment, Imperial College Press. The British Geological Survey archive, Edinburgh 2014. P23 Cement. K (2001) Efflorescence: Causes, Removal, and Prevention. Graniterock website. Accssed on 27 April 2014.: http://www.graniterock.com/technical_notes/efflorescence.html Deborah Architecture of Scotland: Reformation to Restoration (1560-1660), Edinburgh University Press, 1995, p.192 Forsyth, M. (2008). Materials and Skills for Historic Building Conservation Edinburgh Blackwell publishing LTD. Gibbons, P. (1995) Scottish Lime Centre Trust, Historic Scotland Technical Advice Note 1, Preparation and Use of Lime Mortars, Historic Scotland P 34 Heathcote, L. (1998-99). Sandstone: Its properties, Application and Conservation Edinburgh. Edinburgh College of Art archive. P. (89-90), P. 122 Mclean, D. Lost Edinburgh: The Tron Kirk. 03 June 2013, the Scotsman website. Accessed on 21 April 2014: http://www.scotsman.com/lifestyle/heritage/lost-edinburgh-the-tron-kirk-1-2952898 Pitting, Flaking & Blistering, Modes of Stone Decay article. Info Tile website. Accessed on 21 April 2014: http://www.infotile.com/pdfFile/advicetopic/7122011113752.pdf Richardson, C. (1996). Structural Movement. The Building Conservation Directory. Website. Accessed on 27 April 2014 : http://www.buildingconservation.com/articles/movement/movement.htm Rossi-Manaresi et al, (1995) Long-term Effectiveness of Treatments of Sandstone’, ICCROM International Colloquium on methods of evaluating products for the conservation of porous building materials in monuments. British Geological Survey Archive, Edinburgh. P (21-22) The Burra Charter: The Australia ICOMOS Charter for Places of Cultural Significance, 2013. Australia ICOMOS website. Accessed on 27 April 2014: http://australia.icomos.org/wp-content/uploads/The-Burra-Charter-2013-Adopted-31.10.2013.pdf The Tron Kirk, Edinburgh Evening News, 8 Mar 2004, p.9 and 20 Dec 2004, p.21 Trewin, N. H. (2002). The Geology of Scotland. British Geological Survey archive. p.465 Seaward, M.R.D (1979). Lower plants and the urban landscape, Urban Ecology. P217-P219 Wainwrite, M (1986). Lichen removal from an engraved memorial to Walt Whitman. Association for Preservation Technology Bulletin. P46