Timber Decay

Timber Decay in Buildings The conservation approach to treatment

Brian Ridout

XX

ENGLISH

H I S T O R I C Bull

HERITAGE

Spon Press Taylor & Francis Group LONDON AND NEW YORK

SCOTLAND

Contents

Foreword Preface Illustration acknowledgements

Part 1: Nature of Wood 1

xi xiii xvi

1

Origins and durability of building timber 1.1 Introduction 1.2 Structural polymers 1.3 Cell wall 1.4 Structure of wood 1.4.1 Softwoods and hardwoods 1.4.2 Structure of softwoods 1.4.3 Structure of hardwoods 1.5 Functional tree: differences between softwood and hardwood species 1.5.1 Juvenile or core wood 1.5.2 Mature wood 1.5.3 Over-mature wood

9 13 14 15

Sorption of water by timber 2.1 Natural hygroscopicity 2.1.1 Ray cell orientation 2.1.2 Latewood/earlywood orientation 2.2 Age-related changes 2.3 Effects of decay on moisture sorption

16 16 17 17 17 19

Part 2: Agents of Decay and Traditional Treatments

21

2

3

Post-harvest changes and decay 3.1 Effects of moisture content

3 3 3 5 7 7 8 9

23 23

CONTENTS 3.2 Nutrient availability after conversion: the potential for decay 3.3 Damage caused by insects 3.3.1 Cell-content feeders 3.3.2 Cell-content and partial cell-wall feeders 3.3.3 Cell-content and cell-wall feeders 3.4 Decay caused by fungi 3.4.1 Moulds and stains 3.4.2 Soft rot 3.4.3 White rot 3.4.4 Brown rots 3.5 European hazard classification for building timbers 3.6 Physical/chemical decay 3.6.1 Thermal damage 3.6.2 Visible and ultraviolet (UV) light 3.6.3 Surface degradation caused by mechanical damage 3.6.4 Chemical decay 3.7 Acidity and corrosion of metals by timber

24 25 27 27 27 27 28 28 29 29 30 31 31 32 32 32 35

Death watch beetle (Xestobium rufovillosum) 4.1 Brief history of the beetle and the development of insecticides 4.2 Biology of the death watch beetle 4.3 Monitoring current activity and population 4.4 Methods of treatment 4.4.1 Defrassing 4.4.2 Spraying 4.4.3 Injection 4.4.4 Paste treatment 4.4.5 Smoke treatment 4.4.6 Insect traps

37 37 39 48 49 50 50 52 53 53 54

Furniture beetle or woodworm (Anobium punctatum) 5.1 Brief history of the beetle and its treatment 5.2 Biology of the furniture beetle 5.3 Monitoring current activity and population 5.4 Methods of treatment and control 5.4.1 Spray and injection treatments 5.4.2 Fogging 5.4.3 Freezing/heating 5.4.4 Fumigation

55 55 58 60 62 62 63 64 64

Minor decay insects 6.1 House longhorn beetle 6.1.1 Methods of treatment 6.2 Powder post beetles (Lyctidae, Bostrychidae) 6.2.1 Methods of treatment 6.3 Weevils (Curculionidae) 6.3.1 Methods of treatment

65 65 67 67 70 70 71

VI

CONTENTS 6.4 6.5 6.6

Wharf borer {Nacerdes melanura) 6.4.1 Methods of treatment Pinhole and shothole borers (Scolytidae, Platypodidae) Risk of termites in Britain 6.6.1 Methods of treatment

71 72 72 73 75

7

Dry 7.1 7.2 7.3

rot History of dry rot and early treatments Biology of dry rot Traditional treatments 7.3.1 Exposing the full extent of the infection 7.3.2 Cutting back past the last signs of decay 7.3.3 Wall irrigation/toxic box treatments 7.3.4 Spray and paste treatments 7.3.5 Fungicidal renders 7.3.6 Heat treatments 7.3.7 Timber reinstatement 7.4 Detection of dry rot with dogs

76 76 80 86 86 87 87 88 88 89 89 89

8

Wet rots and minor decay fungi 8.1 Identification of fungi in buildings 8.2 Category A: Moulds 8.2.1 Damage to timber 8.3 Category B: Jelly fungi or plaster moulds 8.3.1 Elf cup fungi (mostly Pezizaceae) 8.3.2 Pyronema spp. (Pseudoascoboleae) 8.3.3 Damage to timber 8.4 Category C: Resupinate fungi 8.4.1 Cellar rot (Coniophora puteana) 8.4.2 Asterostroma cervicolor 8.4.3 Damage to timber 8.5 Category D: Pore fungi 8.5.1 Mine fungus {Antrodia vaillantit) 8.5.2 Oak rot (Donkioporia expansa) 8.5.3 Damage to timber 8.6 Category E: Gilled fungi 8.6.1 Ink cap fungus (Coprinus) 8.6.2 Damage to timber 8.7 The treatment of wet rots

90 90 90 90 91 92 92 92 92 92 93 93 93 95 95 97 98 98 98 98

9

Timber pretreatments 9.1 Brief history of pretreatments 9.2 Modern water-based preservatives for pressure impregnation 9.3 Organic solvent-based preservatives for pressure impregnation 9.4 Diffusion pretreatments 9.5 Dip/immersion pretreatments 9.6 Preservative penetration vii

100 100 102 103 105 105 106

CONTENTS 9.7 9.8 9.9 10

Metal corrosion in pretreated timber Selection and use of pretreated timber Disposal of pretreated timber and waste

Regulations, legislation and charters 10.1 European Standards for wood preservation 10.2 Controls on the manufacture and use of pesticides 10.3 Protection of bats 10.4 Control of Substances Hazardous to Health (COSHH) Regulations 1994 10.5 Construction (Design and Management) Regulations (CDM) 1994

Part 3: Effects of the Building Environment on Timbers 11

12

107 107 108 110 110 110 111 113 115 117

Drying and wetting: A historical perspective on timber decay within buildings 11.1 Changes in moisture content after felling 11.2 Air drying 11.3 Kiln drying 11.4 Moisture, the key to decay 11.5 Air temperature and relative humidity 11.6 Water absorption along the grain 11.7 Water absorption across the grain 11.8 Some consequences of conversion 11.9 Timber replacement and re-use 11.10 From oak frames to brick and softwood 11.11 Some consequences of war 11.12 Durability of old and modern timbers compared 11.13 Use of second-hand timbers 11.14 Timber and walls

119 119 120 121 125 127 128 130 131 133 133 136 136 139 140

Fire damage and dereliction 12.1 Dry rot and fire damage 12.2 Weatherproofing 12.3 Removal of debris and timber cleaning 12.4 Stripping interiors 12A.I Position within the building 12.4.2 Floors, panelling, joinery and linings 12.4.3 Storage 12.4.4 History of dry rot 12.5 Progression of fungal assemblages 12.6 Dereliction 12.7 Modes and rates of drying 12.7.1 First-stage drying 12.7.2 Second-stage drying

142 142 142 143 144 144 147 148 149 149 150 151 152 152

viii

CONTENTS

13

12.8 12.9

Drying by increased ventilation Accelerated drying 12.9.1 Air blowers 12.9.2 Dehumidifiers 12.10 Isolationof timbers and the mobilization of wall salts

153 153 155 155 157

Monitoring the building environment 13.1 Moisture meters and their accuracy in timber 13.1.1 Moisture monitoring by the oven/balance method 13.1.2 Remote moisture monitoring 13.2 Brickwork and masonry moisture monitoring 13.3 Automated remote monitoring 13.3.1 Environmental monitoring 13.3.2 Leak detection 13.3.3 Multiparameter moisture monitoring

160 160 162 163 165 165 166 166 166

Part 4: Evolving a Philosophy for Timber Treatment

169

14

171 171 172 173 174 176

Resolving conflicts between treatment and conservation 14.1 Remedial industry 14.2 Precautionary treatments 14.3 Guarantees 14.4 International and national policies on minimal intervention 14.5 Natural control of decay 14.5.1 Natural insect population regulators within the building ecosystem 14.5.2 Environmental control of death watch beetle: Westminster Hall 14.5.3 Environmental control of furniture beetle 14.5.4 Environmental control of dry rot 14.6 Holistic approach to dry rot treatment 14.6.1 Evaluate the cause and level of fungal activity 14.6.2 Evaluate moisture levels and distribution 14.6.3 Locate and assess all timbers at risk 14.7 Conclusions

176 180 184 184 187 187 187 187 187

Appendix A: Analytical approach to preservative treatment A.I Introduction to the use of analytical keys A.2 Key to the treatment of death watch beetle A.3 Key to the treatment of furniture beetle A. 4 Key to the treatment of decay caused by fungi, including dry rot

189 189 190 192 194

Appendix B: Dry rot case studies B.I Case study 1: Arniston House, Midlothian B.2 Case study 2: Bute Hall, University of Glasgow

197 197 198

ix

CONTENTS B.3 B.4 B.5 B.6

Case study 3: Walsworth Hall, Gloucestershire Case study 4: Sea Captain's House and Calendering Works, Dundee Case study 5: Lees Court, Kent Case study 6: Christchurch, Waterloo, Merseyside

References and bibliography Index

199 202 206 207 210 222