Timber Decay in Buildings

Transcription

1 Timber Decay in Buildings The conservation approach to treatment Brian Ridout XX H ENGLISH HERITAGE I S T O R I C Bull SCOTLAND Spon Press Taylor & Francis Group LONDON AND NEW YORK

2 Contents Foreword Preface Illustration acknowledgements xi xiii xvi Part 1: Nature of Wood 1 1 Origins and durability of building timber Introduction Structural polymers Cell wall Structure of wood Softwoods and hardwoods Structure of softwoods Structure of hardwoods Functional tree: differences between softwood and hardwood species Juvenile or core wood Mature wood Over-mature wood 15 2 Sorption of water by timber Natural hygroscopicity Ray cell orientation Latewood/earlywood orientation Age-related changes Effects of decay on moisture sorption 19 Part 2: Agents of Decay and Traditional Treatments 21 3 Post-harvest changes and decay Effects of moisture content 23

3 3.2 Nutrient availability after conversion: the potential for decay Damage caused by insects Cell-content feeders Cell-content and partial cell-wall feeders Cell-content and cell-wall feeders Decay caused by fungi Moulds and stains Soft rot White rot Brown rots European hazard classification for building timbers Physical/chemical decay Thermal damage Visible and ultraviolet (UV) light Surface degradation caused by mechanical damage Chemical decay Acidity and corrosion of metals by timber 35 Death watch beetle (Xestobium rufovillosum) Brief history of the beetle and the development of insecticides Biology of the death watch beetle Monitoring current activity and population Methods of treatment Defrassing Spraying Injection Paste treatment Smoke treatment Insect traps 54 Furniture beetle or woodworm (Anobium punctatum) Brief history of the beetle and its treatment Biology of the furniture beetle Monitoring current activity and population Methods of treatment and control Spray and injection treatments Fogging Freezing/heating Fumigation 64 Minor decay insects House longhorn beetle Methods of treatment Powder post beetles (Lyctidae, Bostrychidae) Methods of treatment Weevils (Curculionidae) Methods of treatment 71 VI

4 6.4 Wharf borer {Nacerdes melanura) Methods of treatment Pinhole and shothole borers (Scolytidae, Platypodidae) Risk of termites in Britain Methods of treatment 75 7 Dry rot History of dry rot and early treatments Biology of dry rot Traditional treatments Exposing the full extent of the infection Cutting back past the last signs of decay Wall irrigation/toxic box treatments Spray and paste treatments Fungicidal renders Heat treatments Timber reinstatement Detection of dry rot with dogs 89 8 Wet rots and minor decay fungi Identification of fungi in buildings Category A: Moulds Damage to timber Category B: Jelly fungi or plaster moulds Elf cup fungi (mostly Pezizaceae) Pyronema spp. (Pseudoascoboleae) Damage to timber Category C: Resupinate fungi Cellar rot (Coniophora puteana) Asterostroma cervicolor Damage to timber Category D: Pore fungi Mine fungus {Antrodia vaillantit) Oak rot (Donkioporia expansa) Damage to timber Category E: Gilled fungi Ink cap fungus (Coprinus) Damage to timber The treatment of wet rots 98 9 Timber pretreatments Brief history of pretreatments Modern water-based preservatives for pressure impregnation Organic solvent-based preservatives for pressure impregnation Diffusion pretreatments Dip/immersion pretreatments Preservative penetration 106 vii

5 9.7 Metal corrosion in pretreated timber Selection and use of pretreated timber Disposal of pretreated timber and waste Regulations, legislation and charters European Standards for wood preservation Controls on the manufacture and use of pesticides Protection of bats Control of Substances Hazardous to Health (COSHH) Regulations Construction (Design and Management) Regulations (CDM) Part 3: Effects of the Building Environment on Timbers Drying and wetting: A historical perspective on timber decay within buildings Changes in moisture content after felling Air drying Kiln drying Moisture, the key to decay Air temperature and relative humidity Water absorption along the grain Water absorption across the grain Some consequences of conversion Timber replacement and re-use From oak frames to brick and softwood Some consequences of war Durability of old and modern timbers compared Use of second-hand timbers Timber and walls Fire damage and dereliction Dry rot and fire damage Weatherproofing Removal of debris and timber cleaning Stripping interiors A.I Position within the building Floors, panelling, joinery and linings Storage History of dry rot Progression of fungal assemblages Dereliction Modes and rates of drying First-stage drying Second-stage drying 152 viii

6 12.8 Drying by increased ventilation Accelerated drying Air blowers Dehumidifiers Isolationof timbers and the mobilization of wall salts Monitoring the building environment Moisture meters and their accuracy in timber Moisture monitoring by the oven/balance method Remote moisture monitoring Brickwork and masonry moisture monitoring Automated remote monitoring Environmental monitoring Leak detection Multiparameter moisture monitoring 166 Part 4: Evolving a Philosophy for Timber Treatment Resolving conflicts between treatment and conservation Remedial industry Precautionary treatments Guarantees International and national policies on minimal intervention Natural control of decay Natural insect population regulators within the building ecosystem Environmental control of death watch beetle: Westminster Hall Environmental control of furniture beetle Environmental control of dry rot Holistic approach to dry rot treatment Evaluate the cause and level of fungal activity Evaluate moisture levels and distribution Locate and assess all timbers at risk Conclusions 187 Appendix A: Analytical approach to preservative treatment 189 A.I Introduction to the use of analytical keys 189 A.2 Key to the treatment of death watch beetle 190 A.3 Key to the treatment of furniture beetle 192 A. 4 Key to the treatment of decay caused by fungi, including dry rot 194 Appendix B: Dry rot case studies 197 B.I Case study 1: Arniston House, Midlothian 197 B.2 Case study 2: Bute Hall, University of Glasgow 198 ix

7 B.3 Case study 3: Walsworth Hall, Gloucestershire 199 B.4 Case study 4: Sea Captain's House and Calendering Works, Dundee 202 B.5 Case study 5: Lees Court, Kent 206 B.6 Case study 6: Christchurch, Waterloo, Merseyside 207 References and bibliography 210 Index 222