Unit 4. Chemical Wood Preservation - Test Your Knowledge

What is a "carrier" and what is its purpose in wood preservation?

A carrier is a substance that you mix with a pesticide in order to help that pesticide reach its target destination. Because most wood preservatives are liquids, they rely on liquid carriers to transport them into the wood during impregnation.

Name and describe the oldest method of wood preservation.

Charring is perhaps the oldest method of preserving wood. Charring is the process of partially burning wood in order to turn the outer layer of wood into charcoal. This outer layer can then protect the inner wood from some types of damage. People first charred wood over 4,000 years ago by plunging round stakes into fire.

True or false: In addition to the heartwood, the sapwood of several tree species is also resistant to decay.

False. The sapwood of all known tree species is very prone to decay. This is true regardless of any natural resistance of the heartwood. Unless you entirely remove the sapwood or treat it with preservative, decay is likely to occur even in durable species.

What are the two most common types of chemicals used to treat internal decay of in-service utility poles?

Fumigants and water-diffusible chemicals.

What is IPM? How might chemical wood preservation fit into an IPM program?

IPM is an ecological approach to pest control. It is based on the habitat and life cycle of the pest. It combines all of the most appropriate pest control strategies into a unified, site-specific plan. IPM plans may include both nonchemical and chemical management methods. IPM is dedicated to managing causes rather than simply treating symptoms. IPM balances the level of control needed with any associated risks. The goal of an IPM program is to reduce pest numbers to an acceptable level in a way that is practical, cost-effective, and safe for people and the environment. In many cases, you can reduce the need for treated wood by using cultural and other nonchemical methods to prevent pest damage. However, for many high-risk situations, the use of treated wood can be a critical part of an IPM program.

Describe the two basic types of wood preservatives.

Most wood preservatives are either water-based or oil-based (also called water-borne or oil-borne). Water-based means that you will apply the preservative to wood in a water carrier. Oil-based means that you will apply the preservative in an oil carrier. The carrier you use will depend on the chemical preservative that you are applying.

Are water-repellent finishes registered pesticides?

No. However, they can be an important part of an integrated wood protection program.

What causes some species of wood to be naturally resistant to decay and insect damage?

The presence of "extractives" in the heartwood. Extractives are chemicals that form as a function of tree growth. Trees pass the extractives (like transporting liquid waste through pipes) along the rays and deposit them in the dead cells of the heartwood. Some of the chemical extractives are toxic to insects and fungi. In this way, they act like preservatives for the wood.

When and how did modern wood treatment first begin?

The roots of modern wood treatment go back to 1831. At this time, people began to impregnate wood with chemicals using vacuum and pressure processes. In addition, a French invention made it possible to test thousands of chemicals as preservatives. Since then, the testing of new chemical formulations has been a never-ending process.

How can water-repellent finishes protect wood from weather and biological pests?

These products seal the wood and prevents wetting by rain, snow, and ice. They also hold pigments on the wood surface. Pigments are important because they give color and absorb heat and harmful ultraviolet rays that otherwise would bleach the wood of its natural color and speed the breakdown of the surface layers. In addition to protection from weather, water-repellent finishes can reduce the risk of some fungi from attacking wood. By controlling moisture in wood, water-repellent finishes can make wood less desirable for decay fungi. However, water-repellent finishes are not a substitute for treated wood or naturally durable wood in applications where the risk of decay or insect attack is high.

How do we define wood preservation today?

Today, we define wood preservation as the process of adding the right amounts and concentrations of toxic or repellent substances to wood. The goal is to upgrade the wood's resistance to biological attack and make it highly durable.

How can dry spots in a utility pole reduce the success of water-diffusible fungicides?

Water-diffusible chemicals use the moisture in wood as a vehicle in which to move through a pole. If you place a chemical in a drier zone of the wood, it will be not be able to diffuse to the wetter sites. In addition, the slower release rate can permit fungi to cause more damage before the chemical reaches them.

How does using a water-based preservative affect the MC of wood? How can you adjust the MC wood after treatment with these chemicals?

When you add a water-borne preservative to wood, the wood swells and increases in weight. Eventually, the water will evaporate from the wood and the wood will shrink back to its pre-treatment dimensions and weight. For some products, you will need to kiln dry the wood after treatment. This will reduce the weight and minimize the problems of shrinkage after the wood is in use.

Give several reasons why naturally durable wood species are now scarce.

• Some species that were once abundant have been decimated by foreign diseases or insects (ex. American chestnut [Castanea dentata]). • Much of the virgin forestland that once grew durable species is now farmland. Other sections have been replanted with nondurable tree species. • Naturally durable trees are typically older trees. However, the young, fast-growing trees that replace the old trees have more sapwood. Sapwood has no natural durability. • The number of people in the world is growing fast. This creates big demands on our forest resources.