Timber Products
Types
• Natural Timbers
• Engineered Timbers
Natural Timbers
• Structural
• Non Structural
Structural Timbers
• BCA Requirements Performance Requirements
– Volume 1
Structural Timbers
• BCA Requirements Performance Requirements
– Volume 1
AS 1684 & Volume 1
AS 1684 & Volume 1
Structural Timbers
• BCA Requirements Performance Requirements
– Volume 2
AS 1684 & Volume 1
Natural Timber
• Different Timbers have different
Characteristics
• Different Strengths
• F5, F7, F8, F11, F14, F17, F22 & F27
• MGP 10, MGP 12 & MGP 15
Grades of Structural Timbers
• AS 1684.2
Timber Grading Methods
• Visual
• Machine Stress Grading
Stress Grading - Visual
• Traditional Method
• Still used in Australia for
– Hardwoods
– Softwood – Large Sections
• Trained Grader
Stress Grading - Visual
• Every piece of timber produced is visually inspected
• Hardwood or Softwood visual grading standards define
rules, as to the types sizes and positions of 20 physical
characteristics that are allowed into each 'group' or
structural grade of material.
• The size and position of knots and other potential strength
reducing characteristics in each piece is compared with the
size and position of these characteristics allowed in the
various grading classifications.
• The highest grades allow fewer and smaller characteristics in
each piece of timber.
Stress Grading - Visual
• Visual Graded Timber are “F” grade
– E.g. F5, F8 F14 etc.
• Structural grading has no correlation with
aesthetic appearance
Structural Defects
Strength Limiting Characteristics -Pith
• In softwoods, pith is the dark spot that was
the upward growing twig when the tree was
very young. It signifies the presence of 'core
wood' or 'juvenile wood'. Where the density
of the wood is low, this can reduce the
strength of the timber. In grading of
softwoods, the visual grader has to estimate
the spacing of the annual rings to determine
whether or not a piece with core wood is
within the specification of this grade.
Strength Limiting Characteristics -Pith
Strength Limiting Characteristics –
Surface Checks
• Surface checks are shallow cracks on the
surface, mainly from the release of residual
stresses on drying. The grader must check all
cracks to see that they are not a split (that
runs from one face to the other), and if a
check (shallow crack) that they are not too
wide, or too long.
Strength Limiting Characteristics –
Surface Checks
Checking
Splitting
• A longitudinal
separation of the
fibres which extends
to the opposite face
of a piece of sawn
timber.
Strength Limiting Characteristics –
Knots
• Depending on the location of the knots,
different limits apply. They are estimated by
the Knot Area Ratio (KAR) which requires a
grader to visualise the knots going right
through the cross-section. The KAR is the
percentage of the cross-section that is taken
up with knots. Different limits on KAR apply
for knots in the margin (outer quarter of the
wide face) and for the centre (central half of
the wide face).
Strength Limiting Characteristics –
Knots
Strength Limiting Characteristics –
Resin or Bark Pockets
• Resin or bark pockets are gaps in the wood
where the growing tree has captured some
bark or resin. The bark or resin may still be
there, but often it has disappeared leaving an
empty dark-coloured pocket. All resin or bark
pockets must have their width and length
estimated. A piece is classed as within the
grade where the pocket is smaller than the
published size limit.
Strength Limiting Characteristics –
Resin or Bark Pockets
Strength Limiting Characteristics –
Wane
• Wane is usually seen as a missing corner, as
the outside of the tree falls within the cross
section. If more than the limiting percentage
is missing, then the piece falls below the grade
specification. Wane is caused by mechanical
damage to the timber during processing
Strength Limiting Characteristics –
Wane
Strength Limiting Characteristics –
Spring & Bow
Spring and bow are deformations in the
unloaded timber. The grader must be able to
estimate how far from being straight the piece is
over the designated lengths.
Bow
• A curve along the
face of a board that
usually runs from
end to end.
Spring
• Warping along the
edge from one end
to the other. This is
most common in
wood that was cut
from the centre of
the tree near the
pith.
Assigning Grades
• Each species of timber listed in the visual
grading standard has been tested (as small
clear specimens) to find the strength of the
wood fibre. This is used to assign a strength
group to each species. Wood with stronger
fibres has a higher strength group indicating
its potential to deliver stronger pieces if there
are not too many strength limiting
characteristics.
Timber Grading Methods
• Visual
• Machine Stress Grading
Machine Stress Grading
Machine stress-grading uses a machine to bend
each piece of timber (generally about its minor
axis). The machine measures the stiffness of the
piece and uses a loose correlation between
stiffness and strength to assign a stress grade.
Machine Stress Grading
Machine Stress Grading
Machine Stress Grading
Machine Stress Grading
• Radiata Pine is the only timber that is Machine
Graded
• Machine Stress Graded Timber is designated
MGP
Tolerances - Structural
• AS 1684 – The Law in regards to Structural
Requirement
Durability of Timber
• Fungal Attack
• Termite Attack
• Thermal Attack
• Chemical/Liquid Attack
Fungal Degradation
• Fungi can be broadly grouped into two main
types,
1. Moulds and stains (i.e. blue stain) usually
only mar appearance (blue stain can effect
impact strength)
2. Rot fungi (white rot, brown rot and soft rot)
can significantly effect strength properties as
they penetrate or break down the cell walls
of wood. – DRY ROT
Dry Rot
• Fungal Decay caused by Serpula lacrymans
• The decayed wood takes on a dark or browner
crumbly appearance, with cubical like cracking
or checking, that becomes brittle and can
eventually crush the wood into powder.
• Eventually the decay can cause instability and
collapse in structures.
Dry Rot
Fungal Degradation – Dry Rot
• Timber is only vulnerable to fungal attack if
the four following conditions are met:
– Moisture
– Oxygen
– Temperature
– Nutrients
Moisture
• Moisture must be present; if the timber
moisture content (MC) is between 0 and 20%,
fungal attack will not occur. Between 20-25%
MC fungal attack is retarded, and fungal attack
occurs when the MC is over 25%.
Fungal Degradation
• Timber is only vulnerable to fungal attack if
the four following conditions are met:
– Moisture
– Oxygen
– Temperature
– Nutrients
Oxygen
• Oxygen must be present; timber that is
completely submerged, saturated, or more
than 600 mm below ground is rarely attacked.
Fungal Degradation – Dry Rot
• Timber is only vulnerable to fungal attack if
the four following conditions are met:
– Moisture
– Oxygen
– Temperature
– Nutrients
Temperature
• Temperature must be in the range of 5° to
40°C; 25° to 40°C is ideal.
• Fungal attack is retarded by higher or lower
temperatures.
Fungal Degradation – Dry Rot
• Timber is only vulnerable to fungal attack if
the four following conditions are met:
– Moisture
– Oxygen
– Temperature
– Nutrients
Nutrients
• Food must be present in the form of
unprotected nutrients (carbohydrates,
nitrogen minerals, etc.). The timber usually
provides these itself, particularly sapwood,
which is normally high in sugars and
carbohydrates. Nutrients in the sapwood can
be protected by preservative treatment.
Fungal Degradation – Dry Rot
• Removal of any one of these four conditions
will prevent fungal attack although, in
practice, it is usually moisture that requires
the greatest consideration.
Fungal Degradation
• Timber is best protected from fungal action
by:
• eliminating contact with moisture, or
• where this is not possible, by using species
with natural durability appropriate for the
application or low durability species or
sapwood preservative treated to a level
appropriate to the hazard .
Durability of Timber
• Fungal Attack
• Insect Attack
• Thermal Attack
• Chemical/Liquid Attack
Termites
• In Australia there are 350 species, but only 30
are regarded as pests.
• Termites feed on cellulose in the Timber
Structure
• This will destroy the Timber structure
Termites
• 3 Types
– Subterranean
– Damp wood
– Drywood
• These Termites are most common
• Mainly found north of Tropic of Capricorn
• Do not need a connection to ground
• H2F Treated timbers are not suitable
Durability of Timber
• Fungal Attack
• Termite Attack
• Thermal Attack
• Chemical/Liquid Attack
Thermal Degradation
• Thermal action on timber causes it to degrade
through combustion of its chemical
components,
• Structural capacity, due to the reduction of its
cross section by charring and to changes in its
mechanical properties of strength and
stiffness as a function of its exposure to high
temperatures.
Thermal Degradation
• Charring occurs at approximately 300° C.
• Charring acts as an insulator.
• Damage still occurs internally due to Chemical
Changes caused by heat.
Thermal Degradation
Thermal Degradation
Thermal Degradation
Durability of Timber
• Fungal Attack
• Termite Attack
• Thermal Attack
• Chemical/Liquid Attack
Chemical/Liquid
• Water will cause timber to swell
• Water will promote Termite/Fungal Activity
• Timber is resistant to Acids with a ph. > 2
• Timber is resistant to Alkaline with a ph <10
Marine Environments
• 3 Zones
– Embedded in Sea Bed
– Between Sea Bed & High Water Mark
– Above High Water Mark
Marine Environment
• The greatest hazard occurs between the sea
bed & High Water Mark
Natural Durability
See Handout
Natural Durability
• Naturally rot-resistant woods
• These species are resistant to decay in their
natural state, due to high levels of organic
chemicals called extractives,
mainly polyphenols.
Durability of Natural Timbers
• Sapwood of any species has little protection
Durability of Natural Timbers
AS 1684
Timber Properties
• AS 1684 Appendix H
– List the “Properties” by species of Natural Timbers
Notes to the Table
Notes to the Table
Notes to the Table
Notes to the Table
Notes to the Table
Notes to the Table
Notes to the Table
Notes to the Table
AS1604.1 Preservative Treatment
Timber Preservatives
• Creosote and modified creosote-based
preservatives, e.g. Tanalised K.
• Light organic solvent based preservatives (LOSP),
e.g. Protim, Tanalised Azure, Timtech Az.
• Copper chrome arsenic preservatives (fixed
waterborne preservatives) e.g. Tanalised C,
Tanalised E, Lifewood, Naturewood, Timtech CX,
Timtech Q.
• Preservative compounds of boron or fluoride e.g.
Polybor, Tanalised B, Timtech BG, Osmose Liquid
Boron, Sodium Fluoride
Creosote
• Timber Based
– Soot found in Chimney
– Used as Food Preservative
• Oil Based
– Coal Tar
– Oil Tar
Creosote
• Oil Based in Australia
– Oil-tar creosote is derived from the tar that forms
during the distillation process used in the
manufacture of petrol.
– The distillation of the tar from the oil occurs at
very high temperatures; around 980°C
Creosote
• Most suited for heavy duty exterior work, such
as
– railway sleepers,
– bridge decking,
– transmission poles,
– marine piles and
– Fencing
– May Achieve up - to H6
Timber Preservatives
• Creosote and modified creosote-based
preservatives, e.g. Tanalised K.
• Light organic solvent based preservatives (LOSP),
e.g. Protim, Tanalised Azure, Timtech Az.
• Copper chrome arsenic preservatives (fixed
waterborne preservatives) e.g. Tanalised C,
Tanalised E, Lifewood, Naturewood, Timtech CX,
Timtech Q.
• Preservative compounds of boron or fluoride e.g.
Polybor, Tanalised B, Timtech BG, Osmose Liquid
Boron, Sodium Fluoride
LOSP
• Light Organic Solvent Preservative
• H2 Termite Protection
• H3 Termite and Rot Protection
• Is not corrosive to metals
LOSP
• This class of timber treatments use white spirit,
or light oils such as kerosene, as the solvent
carrier to deliver preservative compounds into
timber. Synthetic pyrethroids are typically used as
an insecticide, such as permethrin, bifenthrin or
deltamethrin. In Australia and New Zealand, the
most common formulations use Permethrin as an
insecticide, and Propaconazole and Tebuconazole
as fungicides. While still using a chemical
preservative, this formulation contains no heavymetal compounds.
LOSP
• LOSP treated pine is usually machined to the
required lengths and shapes before the
treatment is applied. As a result of this less
pressure is used in the treatment process and
a little less penetration of solution is achieved.
This does not affect the longevity of the
timber, however it means that LOSP timber
must not go in ground and if the timber is cut
the cut ends must be resealed with a suitable
sealant.
LOSP
• LOSP timber is frequently coated with a
protective oil based primer which is usually
pink. This primer is applied to stabilise and
protect timber during storage and installation,
not as a paint primer. As a result it is
recommended that LOSP primed timber be
sanded down to remove the primer before
painting.
LOSP
• Un-primed LOSP timber is natural in its
appearance as the solution used is clear and
hence causes no discolouration of the timber.
Like CCA the timber will weather and discolour
if not stained or painted.
• Dye is usually added to indicate treatment.
LOSP
• LOSP treated timber is non-corrosive to bolts or
nail plates.
• LOSP Treated Timber can be painted, stained or
oiled. If painting is required, oil based
undercoats are recommended.
• Unpainted surfaces exposed to the elements
need regular applications of a high quality
timber finish.
• Any residual solvent evaporates after 8-12 hours
of opening a pack, leaving the timber odour
free.
LOSP
• With good timber for treatment penetration
can be right through the timber. There can be
small amounts of untreated heartwood
present, therefore where the end is exposed a
brush on preservative can be applied. Where
the cut end is butted up against a treated
section, this may not be necessary, or
possible. Heavily planed or rip sawn timber
should not be used as this may reduce the
protective effect.
LOSP
Timber Preservatives
• Creosote and modified creosote-based
preservatives, e.g. Tanalised K.
• Light organic solvent based preservatives (LOSP),
e.g. Protim, Tanalised Azure, Timtech Az.
• Copper chrome arsenic preservatives (fixed
waterborne preservatives) e.g. Tanalised C,
Tanalised E, Lifewood, Naturewood, Timtech CX,
Timtech Q.
• Preservative compounds of boron or fluoride e.g.
Polybor, Tanalised B, Timtech BG, Osmose Liquid
Boron, Sodium Fluoride
Copper Chrome Arsenic (CCA)
• Chromated copper arsenate (CCA) is a wood
preservative used for timber treatment since
the mid-1930s. It is a mix
of copper, chromium, and arsenic formulated
as oxides or salts. It preserves the wood from
decay fungi, wood attacking insects, including
termites, and marine borers. It also improves
the weather-resistance of treated timber and
may assist paint adherence in the long term
Copper Chrome Arsenic (CCA)
• It is a pressure treatment process, where a
water based solution of CCA is applied using a
vacuum and pressure cycle, and the treated
wood is then stacked to dry. During the
process, the mixture of oxides reacts to form
insoluble compounds, helping with leaching
problems.
Copper Chrome Arsenic (CCA)
During CCA treatment, timber is impregnated
with the preservative solution using controlled
vacuum/pressure processes.
• The ingredients and their roles are:
– copper to control fungi
– arsenic to control termites
– chromium to fix the copper and arsenic in the
wood.
Copper Chrome Arsenic (CCA)
• Recognised by Green tint
• Over time small amounts of the CCA
chemicals, mainly the arsenic, may leach out
of the treated timber. This is particularly the
case in acidic environments.
Replacement for CCA - ACQ
• Alkaline copper quaternary
• Water Based Preservative
• The treatment is made up
– Copper as a fungicide,
– and a quaternary ammonium compound,
an insecticide which also augments the fungicidal
treatment
Replacement for CCA - ACQ
• Since it contains high levels of copper, ACQtreated timber is five times more corrosive to
common steel than normal timber
• Suitable Fasteners are required
Replacement for CCA – CAC (B)
• Copper azole preservative
– Copper as a fungicide,
– and a azole co-biocide compound,
an insecticide which also augments the fungicidal
treatment
– Similar to ACQ it is likely to attack steel fixings
Timber Preservatives
• Creosote and modified creosote-based
preservatives, e.g. Tanalised K.
• Light organic solvent based preservatives (LOSP),
e.g. Protim, Tanalised Azure, Timtech Az.
• Copper chrome arsenic preservatives (fixed
waterborne preservatives) e.g. Tanalised C,
Tanalised E, Lifewood, Naturewood, Timtech CX,
Timtech Q.
• Preservative compounds of boron or fluoride
e.g. Polybor, Tanalised B, Timtech BG, Osmose
Liquid Boron, Sodium Fluoride
Boron
• Boric acid, oxides and salts (borates) are effective
wood preservatives
• Borate treated wood is of low toxicity to humans,
and does not contain copper or other heavy
metals.
• However, unlike most other preservatives, borate
compounds do not become fixed in the wood and
can readily be leached out.
• Should not be used where they will be exposed to
rain, water or ground contact.
Types of Treatment
• Vacuum / Pressure Impregnation:
e.g. CCA or Creosote –
Is used to achieve deep protection for piles, poles, fencing, building
timbers and many types of wood used in domestic and industrial
construction.
• Double Vacuum / Immersion:
e.g. LOSP –
Is used for the protection of building timbers not in ground contact,
e.g. cladding, decking and fabricated joinery components.
• Dip / Spray:
e.g. Polybor –
These preservatives are designed to protect timber against insect
attack and should be used for indoor or sheltered situations above
ground. They are popular treatments for softwood house framing
• Creosote, modified creosote, and other oil-type preservatives are most
suited for heavy duty exterior work, such as railway sleepers, bridge
decking, transmission poles, marine piles and fencing.
• Fixed water-borne preservatives, which will not leach out even when in
contact with running water, are most suitable for domestic buildings,
posts, poles, landscaping fencing, cooling towers, decking, cladding, etc.
• Light organic solvent preservatives are designed for timbers not in contact
with the ground. They should be used for factory assembled joinery, e.g.
window frames, and for building at home, e.g. elevated decking, pergolas
and fascias. They are also used to provide protection for garden furniture.
• You may like the effect of natural weathering, but for the best
performance, including long service life, your timber should be treated
with a water repellent stain.
• Treated timber can be painted or stained just like untreated timber. If
paint or stain is not used for the final finish, protection with a water
repellent is recommended for best results
Durability Requirements
Degradation of Other Materials
• Timber is mildly acidic
• Will encourage the oxidisation of metals
Degradation of Other Materials
Construction Techniques to assist
Durability
Construction Techniques to assist
Durability
Construction Techniques to assist
Durability
Construction Techniques to assist
Durability
Construction Techniques to assist
Durability
Mechanical Degradation
Mechanical Degradation
• To reduce this hazard
– Use Timbers > 800kg per m3 in density
Fatigue
Timber Finishes
• Seasoned
• Non Seasoned
• Rough Sawn
• Dressed
What is Seasoned Timber
Seasoning of Timbers
• Open Air
• Kiln Dried
• Combination
Defects
Defects
Defects
Defects
Natural Timbers
• Structural
• Non Structural
Defects
• Visual
– Structural Defects Listed
Sap-Staining Fungi
Sap-staining fungi do not attack the cell walls of the
wood, only the contents of the wood cells, and so
will not decay the timber. The fungus causes a
bluish stain in the wood which may make the wood
useless for furniture making or veneering for
instance. The fungus will thrive in freshly cut timber
or unseasoned timber that has not been properly
stacked, for instance without stickers. Sap-stain will
not occur in correctly seasoned timber. It can be
treated with a preservative that will prevent further
attack and kill the existing fungus.
Blue Stain
• A discoloration that
penetrates the wood
fibre. It can be any
colour other than the
natural colour of the
piece in which it is
found. It is classed as
light, medium or heavy
and is generally blue or
brown.
Machine Burn
• A darkening of the
wood due to
overheating by the
machine knives or
rolls when pieces
are stopped in a
machine.
Pitch
• An accumulation of
resinous material on
the surface or in
pockets below the
surface of wood.
Also called gum or
sap.
Loose Knot
• A knot that cannot
be relied upon to
remain in place in
the piece. Caused by
a dead branch that
was not fully
integrated into the
tree before it was
cut down
Tight Knot
• A knot fixed by
growth or position in
the wood structure
so that it firmly
retains its place in
the surrounding
wood
Wormholes
• Small holes in the
wood caused by
insects and beetles
Insect Attack
Insect Attack
Engineered wood products
• A way to reduce the variability of the material
• Use low quality material to produce a highgrade product
• Use high quality material in high stress zones
• No size limitations (almost)
• Can be made for special applications
Durability
• Is dependant on the Base Timber & Adhesive
• May be treated to H2 or H3
Adhesive
• The Type A phenolic bond, used in structural
plywood manufactured to AS/NZS 2269 and
structural LVL
• manufactured to AS/NZS 4357, will not creep or
break-down in applications involving long-term
• structural performance and/or extreme longterm exposure to weather, wet or damp
conditions. It is a durable, permanent bond.
•
Transport
• Keep timber flat - Timber may twist, bow or cup if
transported in a bent condition. It should be bundled and
stacked at all stages so that it is flat. This is necessary even
for a short trip across town on the back of a truck.
• Protect corners of packs - Part of the care of the timber
is the use of corner protection under straps used to bind
packs.
• Protect seasoned timber from moisture – packs of
seasoned timber must be wrapped in plastic for delivery
and storage on site
Delivery
• Arrange delivery to fit in with construction
sequence –.
If possible, it is best to have the timber members that
will be used first in the process delivered near the top of
any bundles. However, if that is not possible for
delivery, then when stacking the timber in the storage
area, it should be done so that the first used timber is
at the top.
• Unload timber – don’t dump! - Firewood is often
delivered by raising the truck tray and letting all of the
wood roll off onto the ground. The resulting pile of
timber will mean that many pieces are bent or twisted
and will be much harder for carpenters to install
• Use soft slings and protection for timber on
corners of packs
Storage
• Stack timber flat – stacking the timber flat reduces the
chance of the timber warping, twisting, bending or cupping
prior to installation. (Once restrained by the rest of the
structure, deformation in service is less likely.)
• Stack timber off the ground - Keep the timber away from
ground contact. This prevents attack by termites or grounddwelling fungi, and it also stops the wood from absorbing
moisture directly from the ground. Where timber is stacked on
gluts or pieces of wood, the gluts should be of higher durability
timber to prevent fungi and termites from using the gluts as a
route to the timber
Storage
• Stack the timber in order of use - helps to minimise double
handling and to find the pieces with minimum trouble later
• Cover all seasoned timber Water on seasoned timber:
o Makes it more prone to movement or splitting later on as it
dries back out again
o Makes the timber more desirable for fungal or insect attack.
o Makes it harder to paint, and makes protective coatings less
effective.
o Stains the timber.
Storage
• Store appearance products inside building for
as long as possible - With many appearance
products (such as flooring and lining materials) it is
recommended that the material be stored inside the
building for as long as possible (some weeks) prior
to installation. This allows the material to reach
equilibrium moisture content. The timber will change
its moisture content slowly to arrive at a moisture
content, which is stable with the air inside the
building. It is desirable for this to have occurred
prior to installation so that the timber doesn’t shrink
or swell after it is in service. Shrinkage can crack
the product or open unsightly cracks, and swelling
may cause buckling
Storage
Protection during construction
• Minimise the exposure of seasoned timber to weather
• Cover partially completed work whenever possible
• Seal end-grain as soon as possible - End grain of timber
presents the ends of the hollow cells to the atmosphere and
this can give a conduit for moisture to be transmitted deep
into the timber.
Often, the end grain is hidden in the structure, as part of the
detailing.
It is better to seal the end grain of pieces before assembly. In
some cases an end cap may prove the better solution.
• Apply protective seals or paint finishes as soon as
possible – This will preserve the intended appearance of the
timber, and offer improved life of the elements.