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A Preservation Chemical Glossary

Timber preservation works by treating wood to make it unsuitable for attacking organisms. This is generally achieved by impregnating wood with toxic chemicals that poison or make it unpalatable. The main wood preservative chemicals are:

• Creosote: is produced by the high-temperature distillation of bituminous coal. The distillate consists of solid aromatic hydrocarbons, and tar acids and bases. Creosote is toxic to fungi and insects, is relatively insoluble in water, and is generally low cost. The pungent odor, oily finish and it’s propensity to leak and stain surrounding material makes it less desirable in some situations. Creosote is used where timbers are in contact with the ground or in buildings that have a high decay hazard such as railway sleepers. Fence palings and battens. It is also effective in marine structures.
• PCP: or pentachlorophenol (C6CI5OH) was used for many years as a fungicide. It also affords good protection from insects when dissolved in heavy oil. It is ineffective against marine borers. Many countries have banned the use of organochlorines such as PCP, because of their broad toxicity and persistence in the environment.
• TBTO (Tri-N-Butyltin Oxide (C24H54OSn2): is another oil-soluble chemical like PCP. It is generally used with the addition of an insecticide (eg, dieldrin or lindane) to treat exterior joinery. While it leaves the surface clean for finishing work, it does break down in UV light.
• CCA: or copper-chrome-arsenate is a broad spectrum preservative that has no major limitations. The copper and arsenic are the fungicide and insecticide respectively, while the chromium fixes the chemical to the wood. The chemical penetrates wood well, is odorless, and surfaces can be painted once dried. CCA treatment is the most common for outdoor or ground contact uses. The chemical can be used in both terrestrial and marine environments.
• Boron: salts are another broad spectrum preservative, effective against fungi and most insects with low toxicity. The main problem with boron treatment is that it is water-soluble and doesn’t chemically bond to the wood. It can therefore be leached out and can only be used in low hazard environments such as house framing.