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Classification of defects
•Defects due to
A DEFECT IS AN IRREGULARITY OR
ABNORMALITY OCCURING IN OR ON
WOOD WHICH IS RESPONSIBLE FOR
REDUCTION IN STRENGHT
LOWERING OF DURABILITY
CLASSIFICATION OF DEFECTS
OCCURS DURING THE GROWTH OF THE TREE.
MOST COMMON ARE:
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
A SHAKE IS THE SEPARATION OF THE FIBRES
CAUSED BY THE WIND OR BY FELLING.
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
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
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.
DEFECTS DUE TO SEASONING AND
• A CURVATURE ALONG THE FACE OF A
BOARD AND OFTEN OCCURS WHERE
INSUFFICIENT PILING STICKS ARE
USED DURING SEASONING.
CURVATURE ACROSS THE WIDTH OF THE
BOARD AND IS DUE TO THE FACT THAT
WOOD SHRINKS MORE TANGENTIALLY THAN
IT DOES RADIALLY.
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
TWISTING OR WINDING
OCCURS WHEN A PEICE OF TIMBER SPIRALLY
DISTORTS ALONG ITS LENGTH.
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
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.
INTERNAL SPLITTING OF TIMBER WHICH MAY
OCCUR WHEN THE INNER CORE OF CASE
HARDENED TIMBER SUBSEQUENTLY DRIES OUT.
IS THE RESULT OF USING A
DIFFERENT SPECIES OF WOOD FOR
PILING STICKS ( SPACERS OR
BATTENS) WHEN TIMBER IS
STACKED FOR THE SEASONING
WHICH OF THE FOLLOWING STACKS OF TIMBER DO YOU
THINK WILL END UP WITH STICK STAINS AND WHY?
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
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
WORK ON PORTFOLIO:
Common wood defects
Causes – sketches
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
CONDITIONS NECESSARY FOR
FUNGI TO GROW
Moisture – M.C above 20%
Food supply – wood
Oxygen – particular still warm
TWO MAIN TYPES OF FUNGAL
ATTACK ON TIMBER
DRY ROT (BROWN
WET ROT (WHITE
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
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
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
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.
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
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
Wet rot do not spread to adjoining dry timber. Once
the source of moisture is removed the wet rot will be
ERADICATION OF DRY ROT
Increase the ventilation and cure the cause of the
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
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
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
Treat all existing sound timber with three coats of a
dry rot preservative, which can be applied with brush
Replace all timber that has been taken out with
properly seasoned timber.
Think- pair -share
Turn to your partner and
think about ways to prevent
fungus attack on timber then
share your ideas
ALWAYS KEEP ALL TIMBER DRY
ALWAYS ENSURE GOOD VENTILATION. ALL
CONSTRUCTIONAL TIMBERS SHOULD BE PLACED
SO AS TO ALLOW A FREE CIRCULATION OF AIR
ALWAYS USE WELL SEASONED TIMBER.
ALWAYS USE PRESERVATIVE TREATED TIMBERS IN
UNFAVOURABLE OR VULNERABLE POSITIONS.
1.what are THREE conditions necessary for
fungi to thrive on wood?
2.State the TWO main types of fungal attack
3. describe ONE method you will utilize to
treat or prevent fungal attack.