Timber - the Material

1. Timber - the Material • Timber grows on Trees • Properties of Timber • Grading sawn timber • Durability of timber • Specifying and handling timber • Application of timber in buildings • Manufactured wood products

2. Timber Grows on Trees! • Environmental Issues • Growth of trees • Classification of Timber • Processing timber • Sawing logs to give timber • Seasoning • Treatment • Other processing

3. Large trees die by losing leaves then falling over CO2 CO2 CO2 CO2 CO2 emitted as rotting occurs CO2 Growing trees absorb lots of CO2 Untouched/native forest Over long term Carbon in ~ carbon out

4. CO2 CO2 CO2 CO2 CO2 CO2 New trees planted Harvesting trees removes carbon Harvesting removes Carbon Growing trees New trees planted Growing trees Environmental Considerations Managed Native Forest Plantation Over long term Carbon removed from atmosphere >carbon released into atmosphere

5. Hardwoods broad leaf generally higher densities often dark in colour Softwoods needle-like leaves generally lower densities often light in colour Hardwoods and Softwoods Native Australian h’wds include mountain ash brown box spotted gum jarrah common Australian s’wds include radiata pine cypress pine hoop pine douglas fir

6. Tree Growth • New wood on outside of tree • oldest wood on inside of tree • youngest wood on outside • diameter largest at base • one ring (layer) per year • Tree in forest grows towardslight • trunk straight • lower branches die • leaving small knots in wood • Bark protects wood from damage • tree sheds bark each year

7. Pith - the start of growth in the tree • the original sapling • Pith - the start of growth in the tree • the original sapling • Pith - the start of growth in the tree • the original sapling • Sapling - fibrous juvenile wood • becomes pith • Cambium - growth cells • wood cells created on inside • bark cells created on outside • Cambium - growth cells • wood cells created on inside • bark cells created on outside • Cambium - growth cells • wood cells created on inside • bark cells created on outside • Bark - protects wood • new bark made continually • bark falls off each year • Sapwood - newest wood • on outside of tree (~ 1-3 cm) • takes nutrients from root to leaves • Sapwood - newest wood • new wood has thin cell walls • sapwood most effective on outside • Wood - • new wood cells on outside • newest wood takes nutrients to leaves • Heartwood - older wood • cells closed - can’t pass nutrients • storage for waste - extractives • Heartwood - older wood • oldest sapwood becomes clogged • new heartwood added on outside Production of Wood

8. Generally one ring per year • some climates may have more than one growth season per year • fires or disease may produce an extra ring • Growth rings give texture and figure to wood Growth Rings • Early wood • rapid growth at beginning of growing season • thin, large cells - lighter colour • Late wood • slower growth, often limited by lack of water • thick small cells - darker colour • gives the growth ring

9. De-barked log (sapwood & heartwood) Shaped log (some sapwood removed) Conversion 1 - Logs Tree trunk (wood with bark) Log preparation often in forest

10. Wings Winged split Splits Conversion 2 - Log breakdown De-barked log Splits - pith always on edge

11. Further processing Unseasoned timber Stock for seasoned or milled products Conversion 3 - green sawn • Sawing patterns • Back sawn or quarter sawn • Optimising sizes • cut more pieces in most popular sizes

12. Unseasoned Product or - on to further processing Green sawing - Quarter sawn • Growth rings parallel to short edge • Advantages • best grain shows on face • good wearing surface for floors, furniture • radial face preferred for coatings • lower width shrinkage on drying • less cupping and warp than other cuts • can be successfully reconditioned Less common in structural timber • Disadvantages • slower seasoning • nailing on face more prone to splitting

13. Unseasoned Product or - on to further processing Green sawing - Back sawn • Rings parallel to long edge of piece • Advantages • season more rapidly • good figure on face • less prone to splitting when nailing • wide sections possible • few knots on edge • Disadvantages • shrink more across width when drying • more likely to warp and cup • collapsed timber more difficult to recondition More common in structural timber

14. Conversion 5 - Dry Milling • Sized, Planed, Profiled Products • Rough-sawn and seasoned product passed though planer to produce • controlled dimensions • smooth surfaces • prepared edges • specific cross sectional shapes • Docking • removes potential problems from lengths of products • potential weakness eg splits • appearance eg large knots • utility eg holes