Series editors' preface - Wood Tools

Equilibrium Moisture Content (EMC) %
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
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Dry rot safety line
0 5 10 15 20 25 30 35 40 45 50 55 50 65 70 75 80 85 90 95 100
Relative Humidity (RH) %
tubelike conducting veins in the mycelium. In
the final stages of decay caused by those fungi
that continue active in wood near the critical
moisture content the wood itself may be dry
and friable and this has led to the use of the
term dry rot. In the final stages of decay of
wood caused by fungi that require wood to
be comparatively wet for attack to continue
the affected area is itself often wet, hence the
term wet rot (Dawson, 1980; Sutter, 1986).
Requirements for fungal decay have been
reviewed in Chapter 6. As long as wood is
below the fibre saturation point it is immune
from fungal decay; only when liquid water is
available can fungi start to grow. However, it
must be remembered that condensation in the
region of the fibre saturation point may lead
to the availability of free water, and that water
itself is a product of decay. Therefore, 20%
moisture content (typically in excess of 85%
RH) is taken as a stable limit even though the
fibre saturation point is generally around 28%
(Figure 7.4). Suitable temperatures (10–30 °C),
oxygen and a food source (the wood itself or,
in some cases wood finishes) are also
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Deterioration of wood and wooden structures 295
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Average fibre saturation point:
appreciable shrinkage commences
below this point
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Range of
EMC
achieved by
air drying
Range of
EMC as a
result of
central
heating
required. Fungal infestation is not frequently
encountered in furniture collections which are
appropriately housed and well maintained but
may occur in furniture in poor storage conditions
especially when in contact with the
ground (Figure 7.5). Prevention and control
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Range of EMC
without central
heating
Figure 7.4 Graph of the average relationship between the equilibrium moisture content of wood and relative
humidity (figures for different species vary). In terms of decay potential, important positions on this graph are the
fibre saturation point (average 28%) and the dry rot safety line (20%). Note also the range of EMC for air dried
timber (17–23%), the range of EMC without central heating and the range of EMC as a result of central heating
(figures for London, UK, derived from Figure 7.15)
Figure 7.5 The base of a sculpture by Brancusi
showing evidence of fungal decay and insect infestation.
Fungal attack has proceeded along the early-wood
growth. Subsequent death watch beetle infestation has
followed the lines of fungal infestation