Creosote is a tar-based liquid byproduct of coal processing that is widely applied as a wood preservative. Primarily used commercially to treat railway sleepers, telephone poles and large timbers for bridge construction, creosote prolongs the life of any wood structure in contact with soil or concrete, making it a very effective protection for wood fence posts.
Lay out the fence posts parallel to each other and approximately 30 cm (12 inches) apart. Using sawhorses to support the posts will make applying the creosote easier.
Fill a small paint bucket or roller pan with creosote.
Apply a liberal coat of creosote to the base of the fence posts, including the ends. Keep the brush wet with creosote to fully saturate the wood surfaces. Apply the creosote coating to all sides, rolling the fence posts as needed. Saturate each post to a point approximately 15 to 20 cm (6 to 8 inches) above the intended ground level. For example, if the posts will be set in 60 cm (24 inch) deep post holes, coat the posts to a minimum of 75 to 80 cm (30 to 32 inches) from the bottom end.
Allow the applied creosote to soak into the wood for approximately 30 minutes, then apply an additional coating to each of the posts. Remember, the greater the creosote saturation, the better protected the wood is.
Creosote products are available at DIY shops or builders' merchants.
Creosote can permanently stain any porous surface, such as concrete or stone, so set up the application area in a spot where damage will not occur. A ground sheet can be spread under the posts during the application to protect the surface beneath.
Creosote can cause serious skin irritation. Rubber gloves and safety glasses should be worn as protection during this procedure.