Timber and Wood Products

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Timber and Wood Products

• Basic material properties and characteristics.

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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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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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Production of wood
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Variation fibre grain

• The cell structure is designed to serve
  particular functions in a tree.
• Its properties vary in different directions.

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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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Each piece is unique
Quarter sawn hardwood
Myrtle burl veneer
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Properties are variable

• Drying (seasoning) shrinkage
• Strength hardness
• Durability
• Appearance

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Moisture and drying in wood cells
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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 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.

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Shrinkage in sawn sections

• Tangential shrinkage is the highest
• So, the growth rings tend to shorten as the
  timber dries.

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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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Grain, strength stiffness
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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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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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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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Timber products mouldings

• Hardwood or softwood.
• Solid seasoned timber milled to a wide variety of
  shapes.

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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.

beam
bench top
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Timber products curved glulam

• Glue laminated material can be curved.

Curved bar
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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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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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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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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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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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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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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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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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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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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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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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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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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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Jointing

• Timber is a highly versatile material that can be
  shaped and joined easily.

Half housed
Mortice and tenon
Housed
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Jointing methods
Dowel
Biscuit
Overlap
Fixing blocks
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Conclusions

• Timber is a natural product.
• It has been used for centuries.
• Skilled use and understanding of the material can
  yield excellent results.

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