Seasoned wood

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). 

One way to avoid the use of any preservative is to use wood that is naturally resistant to decay. The heartwood of more naturally rot-resistant species, such as oak, can be used untreated. Other woods that last well without treatment are larch, which will last about 10 years in contact with the soil, or up to 20 years if not in contact with soil Western red cedar, which will give service for about 20 years and sweet chestnut, traditionally used for fence palings and posts. Untreated pine lasts for about five years. Well-seasoned wood that has been allowed to dry out evenly is more expensive than greenwood (freshly cut undried wood), but in its favor, it tends to last longer and can be less prone to distortion as it weathers. 

Wood contains water inside its cells and in between cells. When wood is cut (dead), it first loses the free water, and then, more slowly, the cell wall water. This all causes 3-dimensional shrinkage. Ideally, wood should be seasoned, or dried slowly to the point of equilibrium (free water is gone, but there is no loss of cell wall water). If wood is dried too quickly, it may split or crack, because the outer portion is drying and contracting at a different rate from the middle. The outside compresses the more moist inside, which causes the outer part to break. These same reactions can take place if seasoned wood is saturated and then dried too quickly. 

Cold soaking of seasoned wood in low-viscosity preservative oil for several hours or days and the steeping of green or seasoned... 

Treblinka would have required 430 million pounds, or 195,000 metric tons, of air-dried (seasoned) wood. Due to the short notice and brief time that Himmler allegedly allotted for this process, such a large quantity of air-dried wood would certainly have been impossible to get, which is why only fresh ( green ) wood of lower calorific value would have been available. The calorific value of seasoned wood is 3,600 kcal/kg, whereas that of green wood is only 2,000 kcal/kg.113 Therefore the total required quantity of wood would have increased to 351,000 metric tons, and the daily requirement of green wood was thus approximately 1,900 metric tons. Assuming medium-sized trees of 1 cord volume and 1,500 lbs., the total number of trees needed comes to roughly 515,000. 

A dryer used to season wood evaporates 27 kg hr of water from freshly cut greenwood. Air enters the dryer at 40% relative humidity and 47°C leaves the dryer at 80% relative humidity and 37 C. If the entire process operates at 100 kPa, how many m /hr of moist air enter the dryer ... 

The most destructive beetle pests are those which attack seasoned wood in service, e.g. Anobium punctatum, Hylotrupes bajulus, Lyctus brunneus. Only a few species are capable of doing this, but those that do can cause serious problems. They include long-hom beetles, the common house borer or furniture beetle and powder post beetles. Given susceptible lumber and suitable conditions for development, all of the above insects are difficult and expensive, or in some cases impossible, to control. The use of preservative treated wood obviates the necessity for control. 

The strainTFfects due to dehydration are nowhere better illustrated than in the precautions that must be taken to dry and season wood before its use. This problem relates to water removal from capillaries but certainly the dehydration of the hemicelluloses which are in a paracrystal1ine order at the surface of the microfibrils ( ) must play a role. Xylan (4) in hardwoods and galactoglucomannans (IJ ) in softwoods have the characteristics of columnar and sheet hydration, respectively. 

Furniture beetles attack well-seasoned wood, but require openings or fissures in the surface for oviposition of eggs. Finished surfaces, even sandpapered surfaces, discourage oviposition. Transverse surfaces, such as the feet of legs and drawer backs, offer excellent ovipositional sites, however. 

Nevertheless, this type of seasoning has certain effects on the development of the compounds in the oak. In particular, most of the reactions described in the preceding paragraphs do not occur under these conditions (Table 13.18). Compared to naturally seasoned wood, oven-dried wood has a higher content of astringent tannins and bitter coumarins. It contains less eugenol, vanillin and methyl-octalactone, with a majority of the less odoriferous trans isomer. 

Naturally seasoned oak is generally better for red wines than artificially seasoned wood. 

Seasoned Wood - Wood, used for fuel, that has been air dried so that it contains 15 to 20 percent moisture content (wet basis). 

All types of seasoned wood exposed to the atmosphere at 20°C and relative humidity of 60-65% have a water content close to 12% of the dry weight, conditions that are taken as reference conditions. When relative atmospheric humidity increases or decreases, there are increases or decreases of the water content in the wood evidenced by swelling or shrinkage, respectively, in an almost reversible way. 

FIGURE 12.8 Schematic indication of the phenomena occurring on seasoned wood treated with antiseptic agents immediately after the cut. (a) To avoid on the intact pole, subject to unprotected cracks, possible access points for spores and insects, (b) Preferable on poles carved before the antiseptic treatment, in order to avoid the formation of unprotected cracks. 

Cold soaking of seasoned wood in low-viscosity preservative oil for several hours or days and the steeping of green or seasoned wood in waterborne preservatives for several days are methods sometimes employed for posts, lumber, and timbers on a limited basis. The diffusion process employs water-borne preservatives that will diffuse out of the treating solution into the water in green or wet wood. 

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