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Choose Wood Materials Carefully To Prevent Termites and Rot
by Barb Ogg, PhD, Extension Educator
Unprotected wood used outdoors for decks or landcaping can be damaged by termites and decay. To increase the longevity of wood, homeowners have several options, including several types of pressure-treated wood, naturally resistant wood and composite materials made of wood and plastic.
Pressure-treated lumber. Pressure-treated lumber is highly resistant to decay and insects. Through a series of pressure and vacuum cycles, wood preservative is forced deep into wood pores, forming a chemical barrier against termites and decay.
Many people are familiar with green Chromated Copper Arsenate (CCA) treated wood. It has been widely available since the 1970s; literally millions of decks have been built of CCA-treated wood. It is very resistant to termites and decay, but because arsenic is a known carcinogen, this wood will not be available for residential use after January 2004.
The decision to phase CCA-treated wood for residential structures has people asking what to do with existing structures made of this material. The EPA does not suggest tearing down structures made of CCA-treated wood. According to the EPA, people should take common sense precautions, especially when it comes to children. Children should wash hands after playing on structures and keep food from direct contact with CCA-treated wood.
Some non-arsenic substitutes for CCA-treated wood include:
Alkaline Copper Quaternary (ACQ). This treated wood has been used successfully for more than 10 years and has the same green look as CCA treated wood, but does not contain arsenic or chromium. It has been found to have performance characteristics similar to wood treated with CCA. Preserve®, Preserve Plus®, NatureWood® are brand names for ACQ pressure-treated wood.
Copper Boron Azole (CBA). CBA is a copper-based preservative with an organic fungicide. The treated wood is a dark honey brown color and turns a silver-gray after it weathers. Wood products treated with Copper Azole have been used successfully since 1992. Wolmanized Natural Select™ is a brand name for CBA-treated wood.
How long will treated wood last? It depends on the use and location. For best results, it is important to use a treatment level appropriate to the end use. Retention is the amount of wood preservative placed in the wood. When selecting treated wood, refer to the following chart.
Minimum recommended retention for various applications:
|Application||Retention (lbs/cu. ft.)||Uses|
|Above ground decking||0.15 + water repellent||Decking, hand rails, spindles, trellises, gazebos, fence boards|
|Above ground - general use||0.25||Framing lumber, trim and fascia, flooring, sill plates|
|Ground contact||0.40||Deck support posts, fence posts, landscaping|
|Critical structural members||0.60||Permanent wood foundations, building poles|
Naturally Resistant Woods. Naturally resistant woods include redwood, cypress and cedar, but these woods are not long-lasting as treated lumber. For maximum termite and rot resistance, it is important to use the heartwood where resistant compounds are concentrated. Construction common grade wood contains sapwood and will only last a few years with ground contact.
Plastic and Composite Materials. There are two types of lumber products made from recycled plastic. One is 100% plastic. The other type is a composite material made from recycled plastic and waste wood fiber, like sawdust. Plastic and wood composite lumber needs no maintenance or sealing and does not rot, chip or warp. It is also impervious to insects Composite products have guarantees ranging from 10 to 50 years.
Because more than 90% of all termite infestations get started from wood-soil contact, using treated lumber is an important way to prevent termite damage to porches, decks and other wood in contact with the soil.
The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office
University of Nebraska-Lincoln in Lancaster County
Web site: lancaster.unl.edu
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