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Control of Moisture Content in Wood for Mould Growth. IUFRO All Division 5 Taipei 29 Oct-2 Nov, 2007. Dian-Qing Yang. Wood utilisation in buildings. Mould growth in buildings. Wood decay in buildings. Wood deterioration. Mould. Sapstain Fungi. Deep stain (sapwood). BIODETERIORATION
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Control of Moisture Content in Wood for Mould Growth IUFRO All Division 5Taipei29 Oct-2 Nov, 2007 Dian-Qing Yang
Wood deterioration Mould Sapstain Fungi • Deep stain (sapwood) BIODETERIORATION FUNGI WOOD DECAY FUNGI Internal cellulose and lignin Soft-rot Brown-rot White-rot
Problems and economical impact • Aesthetic effect • Health effect • allergens • airborne mycotoxins • Cost for replacement.
Toxic mould • Stachybotrys chartarum (S. atra) • Aspergillus spp. • Fusarium spp. • Paecilomyces variotii
Mould 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 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 tested • Solid wood: jack pine, black spruce and balsam fir • Aspen OSB • Spruce plywood • Medium density fiberboard (MDF) • Gypsum board
Test 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 RHs
Water absorption from air by black spruce wood at 21°C and various RHs
Water absorption from air by balsam fir wood at 21°C and various RHs
Water absorption from air by plywood at 21°C and various RHs
Water absorption from air by gypsum board at 21°C and various RHs
Water absorption from air by various wood materials at 65% RH
Water absorption from air by various wood materials at 79% RH
Water absorption from air by various wood materials at 86% RH
Water absorption from air by various wood materials at 94% RH
Water absorption from air by various wood materials at 100% RH
MC (%) 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% 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% 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
Conclusion 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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