Defect and decay in woods

DEFECTAND

DECAYIN WOODS

NATURALDEFECTS

Cat Face - Fire Scar

A depression in the outer surface of a log

where the tree failed to renew following

an injury, such as an abrasion or fire scar.

Dead or Missing Side

Dead side is decay extending from the

surface to the core of a log, resembling a pie

shape in cross section of the log.

Lightning Scar

Lightning can damage a tree enough

to provide entrance of fungal spores or

cause other structural defects.

Constriction due to climber:

This defect occurs due to climbing

plants. These climbing plants do

considerable damage to the tree by

binding round the stem.

Worm Holes, Insect Damage

Insect burrows that are sufficient to result

in a significant loss of firm wood are not

common in healthy trees. However, storage

for long periods in salt water allows

torpedo borers to do extensive damage and

storage in land decks can allow boring

insects to infest the sapwood.

Burls

Burls are abnormal swellings of the

main stem or branches and are among

the most visible of the stem diseases.

DEFECTS DUE TO CONVERSIONTimbers may sometimes contain defects

due to faulty conversion.

Machine burnt: Defect due to

overheating.

Machine notches: Due to bad holding

and pulling.

Miscut: Careless during sawing of wood.

Imperfect grain: Not matching with

grain alignment.

MECHANICAL DEFECTS

Regardless of how efficiently or carefully the

logging process is conducted, it will result in

some damage to trees when they are felled,

transported, and handled by various

mechanical devices

Undercut

A heavy undercut in a butt log will

reduce the amount of wood available

to cut lumber but no firm wood

deduction is made.

Barber Chair or Slab bed Logs

Barber chair is a very dangerous

occurrence, where the tree splits up the

trunk from the center during the

chopping process.

Shatter or Broken End

Shatter is another defect resulting from

the handling process When chopped, a tree

will often break or shatter if the stem hits a

rock or other object and also can be broken

during skidding, decking, loading, or

unloading.

Multiple Defects

Disease, environmental damage and

equipment damage will all affect the

volume of firm wood in a log.

FUNGALDEFECTS

Stain

Fungi causing stain in wood,

it feeds only on food materials

Stain defect does not affect strength

properties of wood.

Decay

This is observed due to wood destroying

These fungi nourish cell wall material

and break down the cell structure and

enzymatic activities.

This defect reduces the strength

properties of wood.

DEFECTS DUE TO

INSECTS AND

OTHER ANIMALS:

Insects

Insects borers and termites together

constitute one of the most destructive

biological agencies causing defects in

timber.

OTHER ANIMALS

Marine borer:

For example: Crustaceans, Mollusks’, etc.

Birds and mammals

For examples: birds, boar, deer

WOOD DECAYWood decay or wood rot is caused by fungi –organisms that live on other organic matter such as wood.

Brown Decay

Can delete up to 65% of the weight of

the timber.

Tends to spread from cell to cell fast.

Can be on the surface of the timber or

inside the wood.

In the advanced stage, timber often

forms into cube like appearance.

White Decay

Can delete up to 100% of Timber weight

Cells decompose from the center outwards

and completely destroy the cell before

moving onto the next cell.

Can be on the surface or inside the wood.

In the advanced stage, the timber has a

hard appearance.

Soft Decay

Generally wood is a darkish color.

Usually found on the expanded surface

of the wood and extending inwards.

Mold They feed on the contents of the cells

No effect on the strength of the timber

When the timber dries the mold cannot

continue

Molds are indicators of high moisture

content in the air

TABLE 1: CAUSES OF DECAY

Type Agent Environmental Factors

Biological fungi (dry rot, wet rot, moulds and

others) bacteria; actinomycetes; lichens,

mosses and algae wood-boring insect

larvae (woodworm,death watch beetle

and others) carpet beetle, moths, book

lice and silverfish termites

moisture and humidity

air movement

temperature

light

dust

food source

Chemical acids, alkalis and solvents pollution

remedial treatment

Physical mechanical abrasion, general handling

and others, decomposition by physical

agents such as prolonged heating, fire

and moisture

normal use, visitor wear

accidental damage

sunlight, heating, fire,

damp

Radiation ultraviolet light exposure to sunlight

TYPES OF DECAY

Brown cubical butt decay (Phaeolus schweinitzii) in pine.

root decay (Inonotus tomentosus) in pine.

Cedar pocketdecay(Postiasericiomollis). butt decay and aheart decay

Brown stringy trunk decay (Echinodontium tinctorium)

Brown hard trunk decay, advanced stage.

Brown hard trunkdecay, cross section.

Brown hard trunk decay. (Echinodontium tinctorium), trunk decay (Phellinus tremulae),