Quantcast Chapter 4. Wood Deterioration

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CHAPTER 4. WOOD DETERIORATION
Wood preservatives are used to prevent damage by bacteria, fungi, insects, marine borers and other
agents described here. An understanding of these organisms and their damage will contribute to im-
proved wood procurement and construction practices. The various characteristics are summarized
for bacteria and fungi in Table 4-1, for termites and carpenter ants in Table 4-2, for wood boring in-
sects in Table 4-3 and for marine borers in Table 4-4.
4.1 BACTERIA. Bacteria are minute one-celled organisms. A single drop of water may contain
thousands of them.
The sapwood of all wood species appears susceptible; the heartwood less so, in both short and long
term exposures of centuries. The earlywood may be decomposed more rapidly than the latewood.
Bacteria act slowly. Deterioration of wood products by bacteria occurs in wood, such as piles or
wood slats in cooling towers, that is completely saturated or submerged in water for many years.
Upon drying, the outer, degraded area develops a cross-checking that is particularly pronounced on
the tangential face (Figure 4-1).
Bacteria are also known to increase the permeability of sapwood without a noticeable decrease in
specific gravity.
4.2 FUNGI.  Fungi are non-green, flowerless one cell to threadlike organisms that use wood and
other plant materials as a food source.
Wood destroying fungi are composed of millions of microscopic thread-like structures called
hyphae. Initially, individual hyphae develop from germinating spores and spread throughout the
wood. The hyphae secrete enzymes which attack the wood cells, and finally cause the wood to dis-
integrate.
Fungi have four requirements for growth. These requirements are: a food source, oxygen, a
favorable temperature and moisture.
Food - Since fungi are non-green plants, they cannot utilize sunlight to synthesize food materials.
They require an already synthesized food source such as wood. Molds generally feed on material lo-
cated on the wood surface while sapstains utilize food substances stored in the wood cells. The
decay fungi utilize the wood cells themselves thus causing serious strength losses.
Air - All wood decaying fungi need a source of oxygen. Wood stored under water or deep in the soil
does not decay because of the lack of oxygen.
Temperature - The best temperature for wood decay fungi is 75-90 degrees fahrenheit. Decay con-
tinues at a reduced rate or is even dormant at freezing or extremely high temperatures.
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