Creosote is a wood preservative that is generally used in industrial applications such as railroad ties, telephone poles, and pilings. It is not used for commercial purposes where the end product will be used for and around people. From a distance it has a sweet smell, but as you get closer to the treated item, the smell is overwhelming and can be harmful. If an item treated with creosote comes into contact with the skin, it can cause a problem such as a rash. This is one of the oldest commercially used preservatives. It is a brownish / black oil that is distilled from coal tar. It has been very successful in prolonging the life of wood in contact with the ground or in humid conditions that favor the promotion and longevity of fungi. The preservative is pressed into the wood using a special pressure treatment vat.
Once the creosote is in the wood, it will not leach out with water. It also has high toxicity and therefore fungi cannot attack wood for decades. It penetrates wood easily under a pressure treatment system and is cost effective.
Creosote is not available to homeowners for use around the house or farm. In fact, it should never be used where farm animals or humans come into contact with it. In the south, a problem arose many decades ago in which woodpeckers were attracted to the smell of creosote and pecked holes for nesting in utility poles and telephones. They would proceed to lay their eggs that never hatched due to the toxicity of creosote. The final solution was to send a wire mesh around the post at the height at which these woodpeckers normally build their nests. If this had not been done, the population of these large woodpeckers could have seriously declined.
Another note of interest regarding creosote treated timbers is recycling them once they have completed their useful service, such as old railroad ties. Some people have bought old railway sleepers to use in construction, as in some kind of log house. The interior of the house is finished in a conventional manner and the exterior can be finished with rough sawn lumber. Therefore, the core of the house is built with old railroad ties. Bad idea! I knew of a couple who lived in such a house and then they noticed that their cats were dying of cancer. The doctors’ advice was to get out of the house and demolish it.
I have seen people rushing along the train tracks picking up old sleepers that broke into manageable pieces during their removal from the rail platform. People were gathering these pieces to use as firewood. The end result of this practice can only be health problems. Creosote cannot be painted over so the black surface is something one will have to be content with. Even with the old creosote woods used for posts, a good paint will last a short time as the wood preservative seeps through the paint.
If one could get a bucket of creosote and paint it on the wood before using it as a fence post or other ground contact purpose, it is a waste of time as it will do little to deter rot in anything other than a short term. . This also applies to pure tar. If you want to prevent rot in any use susceptible to rot, it is recommended to obtain pressure-treated materials from a wood depot. What they sell to the public will be considered safe for their end use and will save time and money in the long run. If you try to be a homegrown wood technologist, you are doomed in your endeavor.