Creosote preservatives protect wood from pests, bacteria and fungi, preventing damage and improving service life for wood in adverse conditions. Some boat manufacturers also use creosote-treated timbers when building wooden boats, as creosote is toxic to aquatic pests that bore into wooden hulls. In addition to its pesticidal, fungicidal and antibacterial properties, creosote naturally repels water, preventing warping and rotting for timbers in damp environments.
Most timbers treated with creosote find use in outdoor settings, often as free-standing or solitary timbers. Common uses for creosote-treated timbers include railroad ties, utility poles, fencing and marine pier posts. Creosote cannot be used to preserve timbers used in residential construction or outdoor furniture due to its toxic properties and because the substance is difficult to apply in these situations.
Most of the creosote used in wood preservatives is coal tar creosote. Coal tar creosote is a by-product of the coal distillation process. Coal tar creosote is actually a mix of several different substances that get left at the bottom of the distillation column due to their very high boiling points. Coal tar creosote is a viscous, dark green liquid, and timbers treated with the substance turn a very dark brown or black.
Wood tar creosote, produced by distilling resins collected from a variety of different trees, is a much lighter, less toxic substance than coal tar creosote. However, coal tar creosote is more common as it is cheaper, easier to produce and stronger than its wood tar counterpart.