Defects in timber
Grade 8
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objectives
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What are defects in timber
Types of timber defectives
knots
Shakes
Waney edge
Dry rot
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knots
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Knots
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Knots
• Where a branch has grown out of a tree
the grain in the trunk becomes very
twisted. When this is cut through during
conversion the result is a weaker board
and one which is difficult to work. Dead
knots occur in some softwoods
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knots
• These are
distinguished from
live knots because
they show a black line
round their
circumference and
they sometimes fall
out of the wood
leaving a hole.
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Shakes
• These are splits along
the grain of the wood.
• Heart shakes and star
shakes are very
similar; they radiate
from the centre or
heart (see drawing)
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shakes
• Cup or ring shakes follow
the annual rings.
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shakes
• End splits are caused
by rapid drying from
the end grain
• Shakes may occur
during the felling or as
a result of faulty
seasoning.
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Waney edge
• When the outside of
the tree is left as part
of a board it is called
the waney edge. .
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Dry rot
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Dry rot
• This is caused by a fungus growth which
lives on the wood and thus destroys it. It
attacks wood in damp, unventilated
positions causing it to dry up and crumble
into dust.
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Fungus Attack
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Fungus Attack
• There are some more or less harmless
fungi which affect timber. The result is
usually to stain the wood with grey streaks
or patches. This kind of fungus spoils a
decorative white wood like sycamore
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Insect Attack
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Insect Attack
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Insect Attack
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Insect Attack
• There are several vaneties of insect that attack
wood. One that does serious damage to
furniture is the common furniture beetle.
• The beetle lays its eggs in cracks and crevices
of the wood. These hatch into small worms
which burrow into the wood. They continue to
eat their way through the wood for up to two
years. The worms then change into beetles and
come out leaving a woodworm hole.
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Insect Attack
• It is thus possible for wood to be affected by
woodworm for a long time before the woodworm
holes are seen. The beetles are very smallabout the size of a pin head-and light brown in
colour. They are active in the summer months
and during this time they fly about and lay their
eggs on furniture. They are very fond of the
plywood backs of cupboards. Although little can
be done about the worms in the wood, several
preparations are on the market which poison the
beetles as they come out and destroy any eggs
laid" on the surface.
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Dutch Elm Beetle.
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Dutch Elm Beetle.
• This is a fungus which is spread very
rapidly through elm trees by a small
beetle. The fungus kills the tree but the
timber, though not perfect, can be used.
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classwork
Question
• 1. Show ,by means of sketches what you
understand by the following: star shake,
knots, cup shake, waney edge
• 2. Write down what you know about the
common furniture beetle
• 3. Name a fungus which destroys wood
particular damp unventilated postion
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