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Control of Moisture Content in Wood for Mould Growth

Dian-Qing Yang

IUFRO All Division 5Taipei29 Oct-2 Nov, 2007

Wood utilisation in buildingsWood utilisation in buildings

Mould growth in buildingsMould growth in buildings

Wood decay in buildingsWood decay in buildings

Wood deteriorationWood deterioration

Soft-rotSoft-rot

Internal cellulose and ligninInternal cellulose and lignin

BIODETERIORATIONBIODETERIORATIONFUNGIFUNGI

BIODETERIORATIONBIODETERIORATIONFUNGIFUNGI

White-rotWhite-rotBrown-rotBrown-rot

• Deep stain (sapwood)Deep stain (sapwood)

Mould and surface stainMould and surface stain

Problems and economical impactProblems and economical impact

• Aesthetic effect• Health effect

– allergens – airborne mycotoxins

• Cost for replacement.

Toxic mouldToxic mould

• Stachybotrys chartarum (S. atra)• Aspergillus spp.• Fusarium spp.• Paecilomyces variotii

Mould growthMould growth

• On virtually any substrate• Can be found almost anywhere• There is no way to eliminate all moulds• The way to control indoor mould growth is to control

moisture.

Limiting conditions for mould growthLimiting conditions for mould growth

• Determine water absorption rates of different wood materials in various humidity conditions.

• Determine minimal water requirement for mould growth on different wood materials.

• Predict mould growth on wood structures in buildings.

Wood materials testedWood materials tested

• Solid wood: jack pine, black spruce and balsam fir• Aspen OSB• Spruce plywood• Medium density fiberboard (MDF)• Gypsum board

Test methodsTest methods

• Condition wood samples to moisture content 8%.• Place samples in environmental chambers at 21°C

and relative humidity from 65% to 100%.• Determine moisture content of samples and inspect

mould growth weekly for 8 weeks.

Water absorption from air by jack pine wood at 21°C and various RHsWater absorption from air by jack pine wood at 21°C and various RHs

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stu

re C

onte

nt

(%)

65% RH

79% RH

86% RH

94% RH

100% RH

Water absorption from air by black spruce wood at 21°C and various RHsWater absorption from air by black spruce wood at 21°C and various RHs

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

65% RH

79% RH

86% RH

94% RH

100% RH

Water absorption from air by balsam fir wood at 21°C and various RHsWater absorption from air by balsam fir wood at 21°C and various RHs

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

sure

Con

tent

(%)

65% RH

79% RH

86% RH

94% RH

100% RH

Water absorption from air by OSB at 21°C and various RHsWater absorption from air by OSB at 21°C and various RHs

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

65% RH

79% RH

86% RH

94% RH

100% RH

Water absorption from air by plywood at 21°C and various RHsWater absorption from air by plywood at 21°C and various RHs

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

65% RH

79% RH

86% RH

94% RH

100% RH

Water absorption from air by MDF at 21°C and various RHsWater absorption from air by MDF at 21°C and various RHs

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

65% RH

79% RH

86% RH

94% RH

100% RH

Water absorption from air by gypsum board at 21°C and various RHsWater absorption from air by gypsum board at 21°C and various RHs

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (

%)

65% RH

79% RH

86% RH

94% RH

100% RH

Water absorption from air by various wood materials at 65% RHWater absorption from air by various wood materials at 65% RH

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

Jack pine

Black spruce

Balsam fir

OSB

Plywood

MDF

Water absorption from air by various wood materials at 79% RHWater absorption from air by various wood materials at 79% RH

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

Jack pine

Black spruce

Balsam fir

OSB

Plywood

MDF

Water absorption from air by various wood materials at 86% RHWater absorption from air by various wood materials at 86% RH

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

Jack pine

Black spruce

Balsam fir

OSB

Plywood

MDF

Water absorption from air by various wood materials at 94% RHWater absorption from air by various wood materials at 94% RH

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

Jack pine

Black spruce

Balsam fir

OSB

Plywood

MDF

Water absorption from air by various wood materials at 100% RHWater absorption from air by various wood materials at 100% RH

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 1 2 3 4 5 6 7 8

Time (weeks)

Moi

stur

e C

onte

nt (%

)

Jack pine

Black spruce

Balsam fir

OSB

Plywood

MDF

MC (%) of wood materials started to be affected by mouldMC (%) of wood materials started to be affected by mould

• Jack pine wood: 19.3 • Black spruce wood: 21.5 • Balsam fir wood: 19.4• Aspen OSB: 20.2• Spruce plywood: 22.7• Medium density fiberboard: 19.3• Gypsum board: 18.2

Time (week) requirement for mould growth on wood materials at 94% RHTime (week) requirement for mould growth on wood materials at 94% RH

• Jack pine wood: 5 • Black spruce wood: 6 • Balsam fir wood: 6• Aspen OSB: 5• Spruce plywood: 5• Medium density fiberboard: 5• Gypsum board: 5

Time (week) requirement for mould growth on wood materials at 100% RHTime (week) requirement for mould growth on wood materials at 100% RH

• Jack pine wood: 3 • Black spruce wood: 6 • Balsam fir wood: 5• Aspen OSB: 2• Spruce plywood: 2• Medium density fiberboard: 2• Gypsum board: 2

Mould growth on various wood materialsMould growth on various wood materials

Conclusion and future effortConclusion and future effort

• Mould growth on wood materials is generally related to the water absorption rates of the materials, usually a material with a higher water absorption rate is easier to be affected by mould than those materials with lower rates.

• Studies on water absorption rates of the wood materials by water intrusion from one side and all sides, as well as the drying speed in different environmental conditions are underway.

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