Date:

Location:

Date:

Location:

Biodeterioration of Wood

Paul Morris, PhD

Research Leader:

Durability and Building Enclosure

Advanced Building Systems Dept.

Presentation Content

Wood chemistry and structure affecting durability

Natural durability of Canadian species

Organisms attacking wood

Types of decay fungi

Factors necessary for biodeterioration

Time required for decay to occur

Decay characteristics of Canadian softwoods

Other influences on decay initiation

• Breaches in treated shell

• Water traps

• Impediments to drying

Molecular Level

Cellulose polymer

• = Ligno-cellulose

• Only a few organisms

can break it down

Phenolic unit

Sugar unit

Wood Chemistry Affecting Durability

• + Lignin resin

Structure of Cellulose Microfibrils

Crystalline Regions

Amorphous Regions

Wood Cell Wall Layers S3 layer (thin)

S2 layer (thick)

S1 layer (thin)

Primary Wall/ Middle

Lamella

Wood Structure

Affecting Durability

Microscopic Level

Tubular cells

Transport water to leaves

Wood Structure

Affecting Durability

Macroscopic Level

Bark

• Protects sapwood

Cambium

• Growth region

Sapwood - Live

• Starch, protein and lipid

• Responds to wounds

Heartwood - Dead

• Extractives, blockages

• No wound response

In Tree Heartwood is Less Resistant

Heartwood durability varies among species

Sapwood protects itself via wound responses

In Service Sapwood is Less Resistant

Heartwood does not change : durability varies

Sapwood loses resistance when dead

Heartwood Durability of Major Softwoods

Perishable Non -Durable

Moderately Durable

Durable Very Durable

Sapwood of all species

Hemlock Douglas-fir Western red cedar

True Firs Larch Yellow cypress

Spruces Southern pine

White cedar

Jack pine

Lodgepole pine

Wood as a Material to Build a Home

Wood as a Home Made of Food

Wood as Part of The Carbon Cycle

Decay

Growth

Maturity

Death

Utilisation

Insects: Carpenter Ants

• Prefer softer woods

• Don’t eat the wood

• Not affected by copper

preservatives

• Serious near forests

Insects: Subterranean Termites

• Related to cockroaches

• Live in colonies

• Eat any wood or cellulose

• In Canada, found in S.

Ontario, East Vancouver

island, Sunshine coast,

Okanagan. Warmer, drier sites

• Serious damage in buildings

Insects: Wood Boring Beetles

• Typically infest logs

• Larvae tunnel in cambium

and/or sapwood

• Increase due to climate

change: Mountain pine beetle

• Occasional reports in treated

wood

• Adults don’t eat as they chew

their way out

Marine Borers

• Salt water only

• Gribble is a crustacean

• Honeycomb of tiny holes

• Shipworm is a molusc.

• Larvae drift in plankton

• Serious damage in 1 yr

Relative Economic Impact of

Organisms Attacking Wood in Canada

Bacteria

Marine borers

Insects

Fungi

Colonisation Sequence

Bacteria Sugars and nitrates* No*

Mould Starch, protein and lipid No

Stain Starch, protein and lipid No

Soft-rot fungi Ligno-cellulose Yes

Decay Ligno-cellulose Yes

Organism Food Effect on Strength

* May attack ligno-cellulose and affect strength in special circumstances

Bacteria Tunnels in Wood Cell Wall

Soft Rot Cavities in Wood Cell Wall

Wood-Rotting Basidiomycetes: Two types

White-rot Break down ligninwhite

• Typically colonise from the air

• Prefer hardwoods such as aspen

• Rate of strength loss slow

• Wood ends up soft but fibrous

Brown-rot Oxidise lignin brown

• Typically colonise from the air

• Prefer softwoods such as SPF

• Rate of strength loss fast – depolymerize cellulose first

• Wood ends up cracked into cubes

White Rot on OSB

Brown Rot on Lumber

Time Taken for Detectable Reduction

in Mechanical Properties

Time to detectable reduction in mechanical properties =

time for decay initiation

+ time for extensive growth

+ time for depolymerization of cellulose

+ time to inspection or failure

Time for Decay Initiation

Time to decay initiation =

Time to reach adequate moisture content

+ Time for colonisation sequence

+ Time for Basidiomycete to arrive

+ Time for Basidiomycete to establish

Unless there was already decay in the standing tree, not killed by KD

Time for Extensive Growth

Laboratory Test Fungi

• Limited number used

• Selected for reliability of growth

• Selected for high rate of growth

• Selected for high rate of decay

• Grown under optimal conditions (especially moisture)

Real Life Conditions:

• Wide range of fungi might colonize

• Some weaker than others

• Some slower than others

• Some decay faster than others

• Grow under variable conditions

Time for Depolymerization of Cellulose

Loss in strength per week on very small (≤19mm) test samples caused

by brown rot under ideal conditions in laboratory tests

Sapwood

• 60% loss compression perpendicular to grain

• 40% loss compression parallel to grain

Douglas-fir heartwood

• 25% loss compression perpendicular to grain

• 15% loss compression parallel to grain

Time to Inspection or Failure

Critical infrastructure is typically inspected regularly

• Inspection of wood bridges is a whole other topic

• Decay can start, progress undetected and stop when constrained by

− Preservative

− Moisture content limitations

• Decay can remain undetected for years

Incidents of failure of wood in critical infrastructure are rare

• Utility poles fail in ice storms and hurricanes

• You very rarely hear “the wood is rotting, run for your lives”

The fungus fruitbody is like the flower of a plant

30

A Fungus Fruitbody May Indicate the

Presence of a Decay Pocket

Not a decay fungus A decay fungus

Air

Factors Necessary for Decay

Water Food

Fungus

Food

Temperature

32

Climate Change Increasing Decay Hazard

*Scheffer 1971

Setliff 1986

Scheffer Index

(T, Rain)

1940s – 1970s*

33

Climate Change Increasing Decay Hazard

Scheffer Index

(T, Rain)

1970s – 1990s*

*Morris & Wang 2008

Decay Characteristics of BC Softwood Logs

W. red cedar,

Yellow cypress

Douglas fir

W. Larch

Sitka spruce

White spruce

W. Hemlock

True firs

Sapwood Thin Thin** Medium Medium

Heartwood Durable Moderately Non durable Non durable

Time to start* Long (decades) Medium Short (years) Short (years)

Decay rate Slow Moderate Rapid Rapid

Failure Predictable Sudden Sudden Sudden

* On heartwood

** Except medium in US second growth

Decay Characteristics of Treated Wood

W. red cedar,

Yellow cypress

Douglas fir

W. Larch

Sitka spruce

White spruce

W. Hemlock

True firs

Treated shell Thin Thin** Thin Thick

Heartwood Durable Moderately Non durable Non durable

Time to start* Long (decades) Long Medium Long

Decay rate Slow Moderate Rapid Rapid

Failure Predictable Sudden Sudden Sudden

* In un-penetrated interior

Too dry

Too wet

(not enough oxygen)

Just right

Fertile topsoil

Infertile subsoil

Factors Necessary

for Decay Water is #1

Check acts as

capillary Decay starts here

Decay most extensive here

Damage Bolt Holes Notches Cut ends Checks

Mitigating factors:

Preservative mobility

Zinc from galvanizing

Factors Influencing Decay:

Breaches in Treated Shell

Bolt Holes Notches Checks Metal Shoes Damage

Factors Influencing Decay:

Water Traps

Pile tops

Metal Shoes Flashing Bark Paint

Factors Influencing Decay:

Impediments to Drying

Factors Influencing Decay:

Ground Water

Soil Moisture Fresh water

Basidiomycete

Spores

Soft Rot

Mycelium

Basidiomycete

Strand

Basidiomycete

Mycelium

Sources of Fungi

Presentation Review

Wood chemistry and structure affecting durability

Natural durability of Canadian species

Organisms attacking wood

Types of decay fungi

Factors necessary for biodeterioration

Time required for decay to occur

Decay characteristics of Canadian softwoods

Other influences on decay initiation

• Breaches in treated shell

• Water traps

• Impediments to drying

Any Questions?

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