Agriculture Reference
In-Depth Information
The main wood preservatives that have been used in the United States include creosote,
carbolineum, pentachlorophenol (penta), and chromated copper arsenate (CCA). There is
a host of new-generation preservatives based on borates and copper quat (ACQ) that are
more environmentally friendly, including Preserve, NatureWood, and Wolmanized Natural
Select.
Coal tar creosote.
Coal tar creosote (a distillate of coal tar) has been used as a wood
preservative since 1889 in the United States and is still used for treating railroad ties. It is
a dark brown or black, thick, oily substance with a pungent smoky odor. Although it is not
suitable for application inside a barn, creosote-treated railroad ties are ideal for the base of a
round pen or arena. Because creosote contains strong acids and can burn the skin, care must
be taken when handling creosote-treated wood. Due to the dangerous nature of the product,
the U.S. government banned the use of creosote without a license in 1986. Creosote-treated
wood is not paintable. It does resist termites and chewing horses.
Carbolineum.
This thick, brown, oily blend is derived from coal tar creosotes and is
available for application without a license. It can be used safely on trees that are at least
2 inches in diameter, fences, and other exterior applications. It is marketed as an antichew
product as well as a preservative.
Pentachlorophenol.
Penta is a manufactured crystalline organic compound developed
specifically for the wood preservation industry. Penta is normally dissolved in petroleum
oil and forced into the wood with pressure or applied topically, giving the wood the dark
brown color that you see on telephone poles. Penta chemicals can slowly volatize into the
surrounding air and so would not be appropriate for indoor application. Purchase and use
have been limited to certified applicators since 1986. Penta-treated wood is not paintable.
It should not be used where a horse can lick or chew it.
Chromated copper arsenate.
CCA is a waterborne chemical preservative that contains
arsenic, chromium, and copper, and until recently was the most widely used preservative
for pressure-treating posts and fence lumber. The copper in CCA usually gives the wood a
greenish color, and treating wood with it leaves wood paintable. The chemicals in CCA are
bonded tightly to wood, so when used properly, leaching should be minimal. CCA-treated
wood was approved by the U.S. Environmental Protection Agency for use around people,
pets, and plants until its voluntary withdrawal for residential use; it continues to be widely
used in agricultural, marine, highway, and industrial applications. CCA-treated wood emits
no vapors, so is suitable for use inside the barn as well as for fences. Arsenic is a confirmed
human carcinogen; anyone working with CCA-treated wood should take appropriate pre-
cautions.
Borates.
Borates occur naturally in soil, water, plants, and animals. Borate wood treat-
ments are used for protection against termites, beetles, carpenter ants, rot, and fungi. Borate
pressure treatment penetrates to heartwood, so end cuts on treated wood do not need to
be re-treated. Borates are water-soluble, however, and will leach out if used in contact
