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Defects in timber

timber defects

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Defects in timber

  1. 1. DEFECTS IN TIMBER By: Adonica Barnon
  2. 2. Content  Definition  Classification of defects  Natural defects  Knots  Live knot  Dead knot  Shakes  Heart shake  Star shake  Radial shake  Cup shake  Pitch pocket •Rind gall •Twisted fibre •Defects due to seasoning/conversion •Bowing •Cupping •Springing •Twisting •Case hardening •Honey combing •Stick staining
  3. 3. DEFINITION  A DEFECT IS AN IRREGULARITY OR ABNORMALITY OCCURING IN OR ON WOOD WHICH IS RESPONSIBLE FOR ITS:  REDUCTION IN STRENGHT  LOWERING OF DURABILITY  POOR APPEARANCE  DECAY
  4. 4. CLASSIFICATION OF DEFECTS CAUSED BY NATURAL FORCES CONVERSION AND SEASONING BIOLOGICAL ATTACKS
  5. 5. NATURAL DEFECTS  OCCURS DURING THE GROWTH OF THE TREE.  MOST COMMON ARE:  KNOTS  HEART SHAKES  STAR SHAKES  CUP SHAKES  RADIAL SHAKES  PITCH POCKET  RIND GALLS  TWISTED FIBRE
  6. 6. KNOTS  KNOTS OCCURS WHERE THE BRANCHES HAVE BEEN GROWING OUT FROM THE TREE.  DEAD KNOTS OCCUR WHEN THE BRANCH HAS DIED BEFORE THE TREE WAS FELLED. THEY DRY AND FALL OUT OF THE BOARD.  LIVE KNOTS ARE SOUND , AND DEPENDS ON THE SIZE AND QUANTITY, ARE OF NO GREAT DISADVANTAGE.
  7. 7. LIVE KNOT CAN BE WORKED WITH
  8. 8. DEAD KNOT MUST BE REMOVED OR FILLED
  9. 9. SHAKES  A SHAKE IS THE SEPARATION OF THE FIBRES CAUSED BY THE WIND OR BY FELLING.
  10. 10. HEART SHAKE  These are splits occurring in the centre of the tree and running from the pith (inner most part) to wards the sap wood from the medullary (vascular tissues) rays. In some timbers, these splits are hardly visible and in some timbers these are quite permanent. Heart shakes are caused due to shrinkage of interior parts due to age. A heart shake straight across the trunk is not a serious defec
  11. 11. HEART SHAKE
  12. 12. STAR SHAKE These are splits which radiate from the centre of the timber or from the bark (outer side), running in the planes of medullary rays. These occur due to severe frost or scorching heat of the sun.
  13. 13. STAR SHAKE
  14. 14. RADIAL SHAKE CRACKS ALONG THE OUTSIDE OF THE LOG AND ARE CAUSED BY THE RAPID NATURAL DRYING OF THE OUTSIDE OF THE LOG BEFORE IT IS CONVERTED OR BY HEAVY FELLING ONTO THE HARD GROUND.
  15. 15. RADIAL SHAKE
  16. 16. CUP SHAKE These are curved splits which separate the whole or part of one annual ring from an other. These are caused due to the unequal growth of the timber
  17. 17. CUP SHAKE
  18. 18. PITCH POCKET THESE ARE SAUCER SHAPED CAVITIES WHICH ARE FILLED WITH RESIN. THIS FLOWS OUT WHEN THE POCKET IS CUT OPEN.
  19. 19. PITCH POCKET
  20. 20. RIND GALL  THE RIND MEANS BARK AND GALLS MEANS ABNORMAL GROWTH. HENCE PECULIAR CURVED SWELLING FOUND ON THE BODY OF THE TREE ARE KNOW AS RIND GALLS.THEY DEVELOP AT POINTS FROM WHERE BRANCHES ARE IMPROPERLY CUT OFF OR REMOVED.SO THE TIMBER IN THIS PART IS VERY WEAK AND NOT DURABLE.
  21. 21. RIND GALLS
  22. 22. TWISTED FIBRE THESE ARE KNOWN AS WANDERING HEARTS AND CAUSED BY TWISTING OF YOUNG TREES BY FAST BLOWING WIND. THE TIMBER WITH TWISTED FIBRES ARE UNSUITABLE FOR SAWING.
  23. 23. TWISTED TREE TRUNK
  24. 24. DEFECTS DUE TO SEASONING AND /OR CONVERSION  BOWING  CUPPING  SPRINGING  WINDING  WANEY EDGE  CASE HARDENING
  25. 25. BOWING • A CURVATURE ALONG THE FACE OF A BOARD AND OFTEN OCCURS WHERE INSUFFICIENT PILING STICKS ARE USED DURING SEASONING.
  26. 26. CUPPING  CURVATURE ACROSS THE WIDTH OF THE BOARD AND IS DUE TO THE FACT THAT WOOD SHRINKS MORE TANGENTIALLY THAN IT DOES RADIALLY.
  27. 27. SPRINGING  A curvature along the edge of the board where the face remains flat. It is often caused through bad conversion or curved grain. It is also called a crook or a wain
  28. 28. TWISTING OR WINDING  OCCURS WHEN A PEICE OF TIMBER SPIRALLY DISTORTS ALONG ITS LENGTH.
  29. 29. CASE HARDENING  THIS IS AS A RESULT OF TOO RAPID KILN DRYING. THE OUTSIDE OF THE BOARD IS DRY BUT MOISTURE IS TRAPPED IN THE CENTRE CELLS OF THE WOOD.  IS NOT NOTICEABLE UNTIL THE BOARD IS SAWN.  IT CAUSES TWISTING AND BINDING OF THE SAW.  CAN SOMETIMES BE REMEDIED BY QUICKLY RETURNING IT TO THE KILN AND GIVEN A HIGH HUMIDITY TREATMENT THE RE SEASONED.
  30. 30. HONEY COMBING  INTERNAL SPLITTING OF TIMBER WHICH MAY OCCUR WHEN THE INNER CORE OF CASE HARDENED TIMBER SUBSEQUENTLY DRIES OUT.
  31. 31. STICK STAINING IS THE RESULT OF USING A DIFFERENT SPECIES OF WOOD FOR PILING STICKS ( SPACERS OR BATTENS) WHEN TIMBER IS STACKED FOR THE SEASONING PROCESS.
  32. 32. WHICH OF THE FOLLOWING STACKS OF TIMBER DO YOU THINK WILL END UP WITH STICK STAINS AND WHY? STACK A
  33. 33. STACK B
  34. 34. SPLITS AND CHECKS  SEPARATION OF THE WOOD FIBERS THAT DEVELOP MOSTLY ALONG THE END GRAIN OF WOOD AS A RESULT OF THE SURFACE OR ENDS OF THE WOOD DRYING OUT TOO FAST DURING SEASONING.  A SPLIT EXTENDS THROUGH THE BOARD FROM SIDE TO SIDE  A CHECK IS SEEN ON ONE FACE OR AT THE END GRAIN BUT DO NOT EXTEND THROUGHT THE OTHER SIDE.
  35. 35. ASSIGNMENT WORK ON PORTFOLIO:  Common wood defects Types, category, Causes – sketches
  36. 36. BIOLOGICAL ATTACKS ON TIMBER  A biological attack is the intentional release of a pathogen (disease causing agent) or biotoxin (poisonous substance produced by a living organism) against humans, plants, or animals.  FUNGI is the organism that attacks timber
  37. 37. CONDITIONS NECESSARY FOR FUNGI TO GROW Moisture – M.C above 20% Food supply – wood Oxygen – particular still warm air Warmth
  38. 38. TWO MAIN TYPES OF FUNGAL ATTACK ON TIMBER DRY ROT (BROWN ROT) WET ROT (WHITE ROT)
  39. 39. DRY ROT (BROWN ROT)  Mostly found inside, fungi(Serpula lacrymans) eats cellulose in the wood  Wood appears dry and gives off a musty smell  Occurs in damp areas with poor ventilation  Fungi can penetrate through brick walls  able to spread extensively before the damage is first noticed as it favours dark damp environment.
  40. 40. STAGES OF ATTACK 1. STAGE 1 :The tiny spores will germinate on damp timber and send out hyphae ( fine hair-like rootlets), which bore into the timber surface.
  41. 41. STAGE 2: the hyphae branch out and spread through and over the surface of the timber forming a mat of cotton-wool-like threads called mycelium.( at this stage the hyphae can start to penetrate plaster and brickwork in search of new timber to attack
  42. 42.  3. STAGE 3: once the mycelium becomes abundant, a fruiting body (sporophore) will start to form. This fruiting body resembles a pancake with white borders and an orange brown centre. When ripen this fruiting body will discharge millions of spores into the air. These spores may remain dormant for a period of time until they rest on damp timber.
  43. 43. Images of dry rot
  44. 44. WET ROT  Caused by the fungus Coniophora Puteana  Only affects wood with a moisture content above 40%  Therefore usually occurs outdoors – fence posts, windows frames, logs, doors.  Can occur indoors if there is a structural defect- leak in roof , under leaking sinks or baths.  Infected wood has a burned appearance, with white thread like growth
  45. 45. How to recognize Wet rot  The timber becomes considerably darker in colour and has cracks along the grain. Very often the timber decays internally with a fairly thin skin of apparently sound timber remaining often hidden by paint on the surface.  Wet rot do not spread to adjoining dry timber. Once the source of moisture is removed the wet rot will be eradicated.
  46. 46. Images of wet rot
  47. 47. ERADICATION OF DRY ROT  Increase the ventilation and cure the cause of the dampness.  Remove all traces of the rot. This involves cutting away all the infected timber and at least 600 mm of apparently sound wood beyond the last signs of attack.  All affected timber including swept up dust, dirt, old wood shavings and so on must be sealed in airtight polythene bags and arrangements made for incineration. This prevents spreading and kills hyphae and spores.
  48. 48. ERADICATION CONT’D  Strip the plaster from the walls at least 600mm beyond the last signs of hyphae growth.  Clean off all brickwork with a wire brush and sterilise the walls with a brush or spray coat of suitable dry rot fungicide,  Treat all existing sound timber with three coats of a dry rot preservative, which can be applied with brush or spray.  Replace all timber that has been taken out with properly seasoned timber.
  49. 49. Think- pair -share Turn to your partner and think about ways to prevent fungus attack on timber then share your ideas
  50. 50. PREVENTION  ALWAYS KEEP ALL TIMBER DRY  ALWAYS ENSURE GOOD VENTILATION. ALL CONSTRUCTIONAL TIMBERS SHOULD BE PLACED SO AS TO ALLOW A FREE CIRCULATION OF AIR AROUND THEM.  ALWAYS USE WELL SEASONED TIMBER.  ALWAYS USE PRESERVATIVE TREATED TIMBERS IN UNFAVOURABLE OR VULNERABLE POSITIONS.
  51. 51. EXIT SLIPS  1.what are THREE conditions necessary for fungi to thrive on wood?  2.State the TWO main types of fungal attack on wood.  3. describe ONE method you will utilize to treat or prevent fungal attack.

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