BAA1312 : Engineering Material : Timber Part II

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BAA1312 Engineering Material Timber (Part II)
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BAA1312 Engineering Material
Todays objectives

• Able to identify the method of seasoning
• Able to identify the type of timber treatment
• Able to identify the method of timber treatment
• Able to identify the effect to the timber without
  treatment

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BAA1312 Engineering Material

• Shrinkage and Seasoning

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BAA1312 Engineering Material

• Shrinkage and Seasoning (contd)

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BAA1312 Engineering Material

• Shrinkage and Seasoning (contd)

• Timber Seasoning 2 Method
• Air Seasoning
• Kiln Drying

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BAA1312 Engineering Material

• Seasoning Air Drying

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BAA1312 Engineering Material

• Seasoning Air Drying (contd)

• The timber stacked in open-sided sheds to promote
  drying without artificial assistance.
• Stacked about 450 mm clear of the ground.
• This process minimizes damage but this process
  very slow often taking several years to complete.
• This process cheap compare to drying kiln.

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BAA1312 Engineering Material

• Seasoning Drying Kiln

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BAA1312 Engineering Material

• Seasoning Drying Kiln (contd)

• employs a heated, ventilated and humidified
• oven
• the humidity is essential to control the rate of
  
• evaporation of moisture from within the lumber.

Drying Kiln Process
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BAA1312 Engineering Material

• Seasoning Air Drying Drying Kiln (contd)

• There are only 3 factors that affect the drying
  process
• a) temperature
• b) relative humidity
• c) air circulation

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BAA1312 Engineering Material

• Durability

• It refers to long term performance of the
  material.
• Wood can be durable if it well seasoned and kept
  in dry place, immersed in water or buried in the
  ground.
• Heartwood of all species has a very good
  resistance.
• Sapwood is susceptible to decay if not used
  properly in construction.

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BAA1312 Engineering Material

• Treatment

• use effective waterproofing technique after
  seasoning to
• prevent wood destroying
• paints, stains or waterproofing chemicals are
  used to
• make lumber waterproof.
• but none of it is effective when wood is in
  contact with
• ground.
• to protect lumber that is in contact with ground
  or is
• susceptible to decay, the wood need to be
  chemically
• treated.

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BAA1312 Engineering Material

• Treatment (contd)

• Wood need to be chemically treated becausea) To
  prevent destruction from fungi and insectsb) To
  inhibit combustion
• This kind of treatment done by injecting
  chemicals under pressure into the wood fibers and
  is called pressure treatment or preservative
  treatment.
• Treatment to prevent destruction from fungi
  insects is carried out with 1 of 3 classes of
  chemical such as Organic solvent preservatives
  , Tar oil preservatives (example Creosote)
  Waterborne preservatives

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BAA1312 Engineering Material

• Treatment Type of Preservative (contd)

• According to BS 5269 Part 5, they are 3 types of
  preservative.
• Tar-Oil Preservative
• Water-Soluble Preservative
• Organic Solvent Preservative

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BAA1312 Engineering Material

• Treatment Type of Preservative (contd)

• Method of Preservative
• Brush Application
• Dipping
• Open Tank Application
• Pressure Application

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BAA1312 Engineering Material

• Treatment Type of Preservative (contd)

PRESSURE PROCESS
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BAA1312 Engineering Material

• Decay and Destruction

• Untreated timber may decay or destroyed.
• Decay happen due to attack by fungi.
• Early stage of decay / fungal attack
• dramatic decrease in some mechanical properties
• very little loss in component volume
• limited changes in appearance
• Advanced fungal attack
• wood is brittle weak
• destruction can be readily recognized

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BAA1312 Engineering Material

• Decay and Destruction (contd)

• Elements needed for fungal growth are
• proper temperature
• moisture content over 19
• Oxygen
• food (wood fiber)
• Elimination of any one or more of these will
  effectively control the growth of fungal
  organisms.

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BAA1312 Engineering Material

• Decay and Destruction Decay (contd)

• There are two types of decay
• Dry Rot
• Wet Rot
• Dry Rot is most serious of all fungi attack
  because once established, it can spread rapidly
  the spread may be extensive before visible signs
  appear.
• Wet Rot is fungal deterioration that occurs in
  excessively wet lumber.

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BAA1312 Engineering Material

• Decay and Destruction Decay Dry Rot (contd)

• is a type of decay caused by house fungus that
  can live in seasoned
• lumber in somewhat dry condition.
• most serious of all fungi attack because once
  established,
• it can spread rapidly the spread may be
  extensive before
• visible signs appear.

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BAA1312 Engineering Material

• Decay and Destruction Decay Wet Rot (contd)

• is fungal deterioration that occurs in
  excessively wet lumber

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BAA1312 Engineering Material

• Termite Attack

• Attack by insects or marine borers can cause wood
  deterioration but their activity can be
  eliminated through application of heat or steam.
• Termite attack can be prevented by following
  precautionary measures during the construction
  stage
• building concrete foundations
• treating the wood that is in contact with the
  ground
• providing sheet metal shields for all the sill
  foundation lumber.

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the end