Creosoting is the process of impregnating wood with creosote, a dark, oily liquid derived from the distillation of coal tar, to protect it against decay, fungal growth, and insect damage. It has been one of the most widely used wood preservation methods since the 19th century.
Applications
Creosoting has been used extensively in construction and infrastructure for well over a century. Its primary application is in treating timber that will be exposed to harsh environmental conditions, particularly prolonged moisture contact or direct ground exposure. Railroad sleepers (ties), telegraph poles, fence posts, marine piling, and bridge timbers have traditionally been the most common recipients of creosote treatment.
The treatment process typically involves placing the timber in a sealed pressure cylinder, removing air from the wood cells through vacuum, and then forcing heated creosote into the wood under high pressure. This deep penetration ensures long-lasting protection, often extending the service life of treated timber by several decades.
Creosote works by making the wood toxic to the organisms that cause decay. The complex mixture of phenolic compounds, polycyclic aromatic hydrocarbons, and other chemicals creates an environment that is inhospitable to fungi, bacteria, and wood-boring insects.
However, the use of creosote has become increasingly restricted in many countries due to environmental and health concerns. The substance is classified as a probable carcinogen, and its runoff can contaminate soil and water. In the European Union, creosote-treated wood is no longer permitted for consumer use since 2003, though limited industrial exceptions remain. Alternative wood preservation methods, including copper-based treatments and modified wood technologies, have largely replaced creosoting in residential and commercial construction.
Despite these restrictions, creosoted timber remains in widespread use in existing infrastructure, and understanding the material is important for renovation and demolition projects.
Related terms
- Wood preservation
- Pressure treatment
- Impregnation
- Timber decay
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