Dr. Brian Bond of the University of Tennessee Agricultural Extension Service is an expert on wood products and their care, and he offers tips on choosing wood that will last. Wood contains sugars that bacteria and fungi feed on. In an outdoor environment wood products will decay if not properly protected. It's wise to use naturally rot-resistant woods such as redwood and red cedar, which are durable because of the extractive content found in the heartwood of the tree. Heartwood is darker in color than sapwood; cedar heartwood has a pleasant aromatic scent. As you might expect, heartwood is much more expensive than sapwood. Sapwood treated with water-repellent preservative is more durable than untreated sapwood, but it doesn't match the lasting qualities of heartwood. Pressure-treated wood (figure A) is an excellent and less costly alternative to heartwood. This type of wood is treated with copper and arsenic forced into the grain inside high-pressure cylinders. Because the chemicals are fixed in the wood and don't leach out, pressure-treated wood is safe to use in vegetable gardens. When you go to a home-improvement center or lumberyard to buy pressure-treated wood, look for a yellow tag at the end of each piece of timber (figure B). The tag may list the accredited agency that inspected the wood, the treating plant, the year it was treated and the retention level indicating how much chemical has been forced into the wood (any number greater than .40 is good). If you have to cut into pressure-treated wood, you will expose untreated areas that will have to be sealed to prevent rot and insect attack (figure C). Properly treated, the wood should last 15 to 30 years. When you buy pressure-treated wood, it is often moist to the touch because it's soaked in water when it's taken from the pressure chamber. Allow it to sit for three to four weeks before painting so the paint will stick to the surface. It's recommended that you apply any wood preservative first, then a primer coat, followed by two coats of paint.
GUESTS :
Brian Bond
UT Agricultural Extension Service
PO Box 1971
Knoxville, TN 37901-1071
Phone: 865-974-7346
Fax: 865-974-1068
Email: aes.bbond@utk.edu
Website: http://www.utextension.utk.edu
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