6 Wood Discoloration

8.5 Damage to Structural Timber Indoors 211
Table 8.7. Cardinal points of wood moisture content (% u) of some house-rot fungi for
colonization and decay of wood (after Huckfeldt and Schmidt 2005)
Species Minimum for Minimum Optimum Maximum
colonization for decay for decay for decay
(moisture source (mass loss (mass loss (mass loss
20–30 cm away) above 2%) above 10%) above 2%)
Serpula lacrymans 21 26 45–140 240
Leucogyrophana pinastri 30 37 44–151 184
Coniophora puteana 18 22 36–210 262
Antrodia vaillantii 22 29 52–150 209
Donkioporia expansa 21 26 34–126 256
Gloeophyllum abietinum 20 22 40–208 256
Gloeophyllum sepiarium 28 30 46–207 225
Gloeophyllum trabeum 25 31 46–179 191
tent and temperature are important features. However, some of the older data
suffer in so far as they derive from only vague or incorrectly identified fungi.
Data that are based on genetically verified fungi are shown in Tables 2.2, 3.8–
3.11, and 8.7.
Regarding the most important influence on wood decay, wood moisture,
opinion has it that the indoor polypores need moisture above the fiber saturation
range, which often occurs only after wetting with water, whereas the
Coniophora spp. mostly attack wood, which was moisturized by vaporous water
or by contact with damp material. The Dry rot fungus is halfway as it
germinates on contact-wetted timber, but takes water from wet substrates by
capillary mechanism and translocates water in its mycelium to timber for
further growth (Schultze-Dewitz 1985).
In piled Scots pine sapwood samples placed on agar in 2-L Erlenmeyer
flasks, a continuous wood moisture gradient developed within 6 weeks by diffusion
from the agar via the lowest sample, which was water-saturated to the
uppermost air-dried sample (Huckfeldt 2003). Table 8.7 shows that all fungi
subsequently inoculated on the agar near the bottom wood sample degraded
very wet wood. For example, S. lacrymans showed more than 2% wood mass
loss in a sample of 240% final moisture content. The optimum moisture for
decay (mass loss above 10%) varied among the species from 36 to 210% u. The
minimum moisture for decay (mass loss above 2%) was slightly below fiber
saturation and for C. puteana and G. abietinum significantly low at 22% u.
Minimum moisture for wood colonization was for some fungi around 20% u,
whereby the wood sample was 20–30 cm away from the agar as the water source
(Huckfeldt and Schmidt 2005).
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