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
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