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Characterisation and Consolidation of Historical Lime Mortars in Cultural Heritage Buildings and Associated Structures in East Africa

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Characterisation and Consolidation of Historical Lime Mortars in Cultural Heritage Buildings and Associated Structures in East Africa Characterisation and Consolidation of Historical Lime Mortars in Cultural Heritage Buildings and Associated Structures in East Africa Athuman M. K. Ngoma TRIKA-BKN. Bulletin 101, 2009 ISSN 1103-4270 ISRN KTH/BKN/B--101--SE Doctoral Thesis The Artichoke At first glance it seems unappetizing, even forbidding, with the meagre edible matter in its hard exterior. The reward, however, comes in taking it apart, devouring it leaf by leaf. Its leaves slowly become more tender and tastier, until you arrive at the succulent heart. ii ABSTRACT ...........................................................................................................................viii PREFACE ................................................................................................................................ix ACKNOWLEDGEMENTS..................................................................................................... x CHAPTER ONE: INTRODUCTION .................................................................................... 1 1.1 Background and Problem Identification .................................................................... 1 1.2 Restoration of Historical Structure............................................................................. 3 1.3 Objectives, Limitations and Method .......................................................................... 3 CHAPTER TWO: MORTAR AND MORTAR DAMAGE................................................. 5 2.1 Introduction ................................................................................................................ 5 2.2 Historical Mortar........................................................................................................ 5 2.3 Lime Mortar Ingredient.............................................................................................. 6 2.3.1 Lime ................................................................................................................... 6 2.3.1.1 Hydraulic Lime .............................................................................................. 6 2.3.1.2 Hydrated Lime (Ca(OH)2).............................................................................. 8 2.3.1.3 Limestone Calcination.................................................................................... 9 2.3.1.4 Lime Slaking ................................................................................................ 11 2.3.1.5 Lime Storage ................................................................................................ 12 2.3.2 Sand.................................................................................................................. 13 2.3.3 Inclusions ......................................................................................................... 14 2.3.3.1 Marine Shell ................................................................................................. 14 2.3.3.2 Charcoal Particle .......................................................................................... 14 2.3.3.3 Lime Lump................................................................................................... 14 2.4 Mortar Mixing and Hardening ................................................................................. 15 2.5 Mortar Damage ........................................................................................................ 16 2.5.1 Moisture ........................................................................................................... 16 2.5.2 Air Pollution..................................................................................................... 16 2.5.3 Soluble Salt ...................................................................................................... 17 2.5.4 Biological Colonisation.................................................................................... 18 CHAPTER THREE: CONSERVATION AND RESTORATION OF THE CULTURAL HERITAGE ............................................................................................................................ 20 3.1 Conservation............................................................................................................. 20 3.1.1 Compatibility.................................................................................................... 20 3.2 Restoration ............................................................................................................... 20 3.3 Consolidants............................................................................................................. 21 3.3.1 Organic/Polymeric based Consolidants ........................................................... 21 3.3.1.1 Alkoxysilanes or Silanes .............................................................................. 22 3.3.1.2 Epoxy Resin ................................................................................................. 22 3.3.1.3 Acrylic Polymers.......................................................................................... 22 3.3.2 Inorganic Consolidants..................................................................................... 23 3.3.2.1 Alkali Silicate............................................................................................... 23 3.3.2.2 Barium Hydroxide (baryta) .......................................................................... 24 3.3.2.3 Calcium Hydroxide Solution (Ca(OH)2)...................................................... 24 3.3.3 Factors of Success ............................................................................................ 27 3.3.3.1 Short-term Performance ............................................................................... 27 3.3.3.2 Long-term performance................................................................................ 28 i CHAPTER FOUR: HISTORICAL MORTAR CHARACTERISATION TECHNIQUES .................................................................................................................................................. 29 4.1 Introduction .............................................................................................................. 29 4.2 Sampling................................................................................................................... 29 4.2.1 Establishment and Clarification of the Objective ............................................ 30 4.2.2 Visual Analysis and Documentation................................................................ 30 4.2.3 Representative Sampling.................................................................................. 31 4.2.4 Analytical Method............................................................................................ 31 4.2.4.1 Chemical Analysis........................................................................................ 32 4.2.4.2 Microscopical-Mineralogical Analysis ........................................................ 32 4.2.4.3 Additional Analytical Techniques................................................................ 34 4.2.4.4 Physical-Mechanical Analyses..................................................................... 35 CHAPTER FIVE: CHARACTERISATION OF MORTAR FROM THE HISTORICAL BUILDINGS ........................................................................................................................... 36 5.1 Establishment and Clarification of the Objectives................................................... 36 5.2 Visual Analyses and Documentation of Historical Mortars in Stone Town ............ 36 5.2.1 Visual Analyses and Documentation of Entire Historical Buildings............... 36 5.2.2 Visual Analysis and Documentation of Historical Mortars ............................. 37 5.3 Formation of Hypotheses ......................................................................................... 38 5.4 Choice of Analytical Method ................................................................................... 38 5.5 Sampling with Associated Information Recording .................................................. 39 5.5.1 Representative Samples.................................................................................... 40 5.5.2 Sampling........................................................................................................... 40 5.6 Further Analysis ....................................................................................................... 41 5.6.1 Mineralogical Analysis .................................................................................... 41 5.6.2 Physical-Mechanical Analyses......................................................................... 43 CHAPTER SIX: RESULTS OF THE CHARACTERISATION OF HISTORICAL MORTAR................................................................................................................................ 44 6.1 Visual Analysis and Documentation of the Entire Historical Buildings in Stone Town .................................................................................................................................. 44 6.1.1 Architectural Style............................................................................................ 44 6.1.2 Construction Technology ................................................................................. 47 6.1.3 Materials Composition ..................................................................................... 47 6.1.4 Current State of Historical Buildings in Stone
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