6 Wood Discoloration
6 Wood Discoloration
6 Wood Discoloration
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6.1 Molding 123<br />
Molded wood is, however, unmarketable. For decorative purpose, e.g., wall<br />
paneling (Fig. 6.2b), molded wood is unsuitable, as the color spots are not mechanically<br />
removable, but can be only masked by colored paints. Infected wood<br />
is not suitable for various hygienic requirements, e.g., packaging material. In<br />
addition, technological characteristics, for example the gluing of plywood, can<br />
be affected by molds (Wolf and Liese 1977).<br />
Mold growth in buildings is increasingly becoming a problem. Molding<br />
in indoor environments (Thörnqvist et al. 1987) is favored by high substrate<br />
moisture (water activity 0.9–1.0), high air humidity around 95%, warmth and<br />
insufficient ventilation (Viitanen and Ritschkoff 1991b), like in cellars and<br />
bathrooms. According to the German standard DIN 4108 part 2, the relative air<br />
humidity on the indoor surfaces shall not amount to over 80% (Borsch-Laaks<br />
2005). Moisture with following mold contamination can arise from condensation,<br />
flood, and various types of leaks. Excessive insulation after the petroleum<br />
crisis has markedly favored condensation areas (cold bridges), from cellars<br />
to attics, which rapidly become sites of mold growth. Accompanying lifestyle<br />
changes (frequent showers, new cooking methods, inadequate airing of bedrooms)<br />
have led increasingly to the production and accumulation of moisture<br />
in the home. A study in Belgium of isolated molds in homes of patients with<br />
allergic problems showed that more than 90% of those houses were contaminated<br />
by molds of the genera Cladosporium, Penicillium and Aspergillus (Nolard<br />
2004). Cladosporium sphaerospermum infiltrated 60% of the homes and<br />
was responsible for high contaminations, particularly in bedrooms and bathrooms.<br />
Aspergillus versicolor, Penicillium chrysogenum, P. aurantiogriseum,<br />
P. spinulosum, P. brevicompactum, Chaetomium globosum, Stachybotrys chartarum,<br />
andAlternaria alternata are often found on the walls of bedrooms,<br />
living rooms, and kitchens. While Cladosporium herbarum, a phytopathogen,<br />
does not grow in houses, large numbers of spores enter through windows and<br />
doors mainly during the summer months.<br />
Molds may cause health problems. About 200 fungal species produce various<br />
mycotoxins (about 100), of which some are highly toxic to humans and<br />
animals (mycotoxicoses) (Müller and Loeffler 1992; Schwantes 1996; Reiß 1997;<br />
Kiffer and Morelet 2000; Samson et al. 2004). The cancerogenic aflatoxins from<br />
Aspergillus fumigatus and A. flavus in food (agricultural crops, cereals etc,<br />
Meister and Springer 2004) are well known. Human health damage can further<br />
develop by mycoallergies through direct contact with a fungus or inhaled<br />
spores (molds in the living space). Five to 15% of the population suffering<br />
from respiratory allergy has been sensitized to one or several molds. Exposure<br />
of young children to molds and their metabolites may have a “stimulating”<br />
effect on the onset of later allergies (Nolard 2004). Mold allergies also occur<br />
in work environments. <strong>Wood</strong>workers inhale spores of Cryptostroma corticale<br />
and Alternaria species (woodworker’s lung). “Bagassosis” may develop during<br />
bagasse processing. “Suberosis” is due to Penicillium glabrum growing on cork<br />
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