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timber in internal applications
Material Basics
Timber and Wood Products
Basic material properties and characteristics.
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timber in internal applications
Material Basics
The nature of timber
• Timber is a natural product, drawn from the wood in the trunks of trees.
• Its character is consistent with the species of tree and the form and growth over time of the wood in it.
Regrowth in a native forest
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Material Basics
Tree growth• New wood on outside of tree
– oldest wood on the inside– youngest wood on the outside– diameter largest at the base– one ring (layer) per growing season
• Tree in forest grows toward light– trunk is straight– lower branches die– leaving small knots in wood
• Bark protects wood from damage– the tree sheds bark each year
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timber in internal applications
Material Basics
Production of wood
Cambium - growth cells• wood cells created on the inside• bark cells created on the outside
Sapwood - newest wood• on the outside of tree (~ 1-3 cm)• takes nutrients from root to leaves
Heartwood - older wood• cells closed - can’t pass nutrients • storage for waste - extractives
Pith - the start of growth in the tree• the original sapling
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timber in internal applications
Material Basics
Variation: fibre & grain
• The cell structure is designed to serve particular functions in a tree.
• Its properties vary in different directions.
rays
rays
cells
fibres
vesselshardwood earlywood
rays
latewood
softwood
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Material Basics
Variation: species & growth
• Species and genetics: – selected stock or
natural seed.
• Climate:– wet or dry, cold or
warm.
• Arrangement:– native forest or
plantation.
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timber in internal applications
Material Basics
Each piece is unique
Myrtle burl veneer
Quarter sawn hardwood
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timber in internal applications
Material Basics
Properties are variable
• Drying (seasoning) & shrinkage
• Strength & hardness
• Durability
• Appearance
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timber in internal applications
Material Basics
Moisture and drying in wood cells
removed bound waterSeasoned
timber15% MC
100% MC
Unseasoned timber
Growingtree
free water
25% MC
fibre saturation
bound waterPartially seasoned
timber
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timber in internal applications
Material Basics
Benefits of drying
• Drying timber increases its:– strength; – stiffness; – stability– durability; &– ease of fastening.
• It is ideally dried to a moisture content in equilibrium with its service environment.
Checking the moisture content
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timber in internal applications
Material Basics
Timber shrinks as it dries
• It shrinks at different rates in different directions.
• Once dry, it will expand & contract to be in equilibrium with changing local conditions.
Shrinkage from 12% to 25% MC
Radiata pine Rad 3.5% Tang 4%Hoop pine Rad 2.5% Tang 3.5%Cypress Rad 3.5% Tang 4%
Spotted gum Rad 4.5% Tang 6%Karri Rad 4.5% Tang 10%Sydney blue gumRad 5% Tang 9%Grey Ironbark Rad 5.5% Tang 7.5%Mountain ash Rad 6.5% Tang 13%
So
ftwo
od
Ha
rdw
ood
Tangential shrinkage
Radialshrinkage
Longitudinalshrinkage
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Material Basics
Shrinkage in sawn sections
• Tangential shrinkage is the highest;
• So, the growth rings tend to shorten as the timber dries.
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Material Basics
Timber dries at different rates
• Pines have a porous cell structure:– They can be dried very quickly.– Turnaround time from saw to store can
be as low as a week.
• Hardwoods have a non-porous cell structure:– The moisture must diffuse through the
cell wall.– Drying can be very slow.– It must be done carefully.
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timber in internal applications
Material Basics
Grain, strength & stiffness
Direction of grain
Strong parallel to grain & stiff parallel to grain
Weak perpendicular to grain
Properties of the grain
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timber in internal applications
Material Basics
Summary of characteristics
• Timber is a natural material • Each piece is unique in fibre, texture and
colour• Its strength is dependant on the
properties of the wood and the slope of the grain
• It takes up and gives up moisture• It expands and shrinks as it does so• It deteriorates in line with exposure
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Material Basics
Timber products
• Timber is available in a wide range of products and species including: – Solid sawn, moulded and laminated timber;– Veneer;– Plywood; and– Wood panels.
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Material Basics
Timber products: sawn
• Hardwood or softwood.
• Solid timber cut from a log and dried.
• It is a versatile material used for moulding, frames and exposed structures.
• Size is restricted.
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Material Basics
Timber products: mouldings
• Hardwood or softwood.
• Solid seasoned timber milled to a wide variety of shapes.
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Material Basics
Timber products: glue laminated
• Small pieces of timber glued together to form a larger element.
• Used as both a structural and finishing element.
• Size is limited only by transport capacity.
bench top
beam
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Material Basics
Timber products: curved glulam
• Glue laminated material can be curved.
Curved bar
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Material Basics
Timber products: veneer
• Thin layers of solid wood sliced from a flitch or peeled from a log and dried.
• High quality material is used as a decorative finish.
• Lower grade material is used to make plywood, LVL and similar products.
Veneer leaf
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Material Basics
Timber products: plywood
• Layers of veneer glued together so that the grain direction alternates between layers.
• Usually produced in sheets.
• Very good in a structure, as a lining and as a flooring surface.
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Material Basics
Timber products: wood panels
• Panels made from wood or wood fibres bound together with glue, or other binder:– Particleboard– Medium Density
Fibreboard (MDF)– Hardboard– Core board
MDF sheet
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Material Basics
Appearance grading
• Production process of sorting products into groups with similar characteristics & properties.
• Timber identified by calling up a specific grade.
Visual grading
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Material Basics
Grading standards
• AS 1810-1995 Timber - Seasoned cypress pine - Milled products
• AS 2796-1999 Timber - Hardwood - Sawn and milled products
• AS 4785-2002 Timber - Softwood - Sawn and milled products
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Material Basics
AS 2796 Hardwood - Sawn & milled
• This standard defines the requirements for hardwood used for visual applications: architectural (flooring, etc), lining & cladding; &
• It is in two main sections: – product requirements; & – visual grades.
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Material Basics
Appearance grading - rules
• Establish permissible limits on: – gum vein – knot size & frequency (location unimportant)– splits, cracks, checks (size and frequency)– stain (colour), grain uniformity– utility: want, wane, cup, bow, spring, twist
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Material Basics
Grade range
• From select grade– uniform wood with
few natural features
• Through to high feature grade– including lively
natural feature as part of a desirable aesthetic.
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timber in internal applications
Material Basics
AS 2796 Hardwood - Sawn & milled
• Tolerances are established for the major product groups (not grades):– Joinery and dressed boards; – Strip and overlay flooring, mouldings, sawn
boards for feedstock; &– Light decking, lining boards, cladding, facia,
bargeboards.
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Material Basics
AS 2796 Part 1 - distortion
• Bow - depends on thickness
• Spring - dependent on width
• Twist - separate limits for less or more than 25 mm thick
• Cup - 1mm per 100 mm width
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Material Basics
AS 2796 Part 1
• No lyctid susceptible sapwood is allowed. (Lyctids are small wood eating insects.)
• MC anywhere in a piece must be between:– 9-14% for most products including flooring. – 8-13% for parquet & furniture components.
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timber in internal applications
Material Basics
AS 2796 Hardwood - Sawn & milled
• The standard recognises feature as a desirable visual characteristic;
• Therefore, distortion and machining tolerances are associated with product, not grade; &
• The timber can then be specified with the desired appearance for any function.
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Material Basics
AS 4785 Softwood - Sawn & milled
• Layout is similar to AS 2796 with product requirements & visual grades;
• Visual grades are Clear, Appearance, Select, Standard, Utility Grade;
• With radiata, there is a much greater use of industry grades; &
• Terms can vary between companies.
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timber in internal applications
Material Basics
Jointing
• Timber is a highly versatile material that can be shaped and joined easily.
Mortice and tenon Housed
Half housed
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Material Basics
Jointing methods
Overlap Fixing blocks
DowelBiscuit
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Material Basics
Conclusions
• Timber is a natural product.
• It has been used for centuries.
• Skilled use and understanding of the material can yield excellent results.
