Used Motor Oil for Treating Pole Barn Posts

There is far (in my humble opinion) too much bad information posted in social media. Among this bad information is pouring used motor oil on pole barn (post frame) building posts in an effort to extend their service life.

Throughout mid and late 1900’s, many farmers found a way to reuse what they had on their farms, including motor oil. During hard times, especially when it came to farming families, sometimes “making due with what you have” was all a farmer could do to stretch his or her resources.

They would up-cycle excess, old, or used oil into a wooden post treatment to prevent wood rot, as well as keep insects from eating and burrowing into this wood. This was before development of copper based pressure preservative treatments, now in common use.

Motor oil prevented water from penetrating wood, and deterred nature’s decomposers (such as bacteria and fungi, like mushrooms) from doing their jobs.

Many also used diesel fuel mixed with used motor oil, as they believed it assisted in preventing posts from rotting.

To farmer’s joy, it performed much like creosote did to preserve posts. Otherwise untreated wood could last 10 to 15 years, until gravity’s effect pulled oil to the post’s butt ends and when oil at grade became thin, rot would occur.

Back then many farmers weren’t overly environmentally conscious.

With controversial farming methods running rampant, including factory farming livestock and conventional farming with row crops, heavy chemical fertilizers and pesticides, dumping oil on posts didn’t seem like a big deal. 

However, used motor oil is dangerous. It is known to contain lots of pollutants, including heavy metals such as lead, arsenic, chromium, zinc and barium.

In addition to these heavy metals, there are also polyaromatic hydrocarbons (PAH); which can make up 30% of this used oil. These hydrocarbons can linger for several years in our environment, especially within sediment in streams and lake beds. While toxicity regarding humans is limited due to inconsistencies, there has been a link between these compounds and an increase in lung, skin, and bladder cancers. In animals, however, studies have proven certain polyaromatic hydrocarbons can cause a variety of problems. Reproductive systems, immune systems, and even nervous systems have been affected in various ways, even leading to significant developmental differences. As for cancerous effects on animals, one PAH in particular has proven to be a leading culprit: Benzo(a)pyrene. This particular hydrocarbon can be found in significant amounts in motor oil used to treat posts: as much as 22 PPM (parts per million)!

Oil doesn’t dissolve in water. It lasts a long time and sticks to everything from beach sand to bird feathers. Oil and petroleum products are toxic to people, wildlife, and plants. One quart of motor oil can pollute 250,000 gallons of water! Used motor oil is the largest single source of oil pollution in lakes, streams, and rivers. Americans spill 180 million gallons of used oil each year into our nation’s waters. This is 16 times Exxon Valdez’s spill in Alaska!

As a more practical and safe solution, properly pressure preservative treated columns can (and do) last several lifetimes (read more here: https://www.hansenpolebuildings.com/2020/09/pressure-treated-post-frame-building-poles-rot/). Still not convinced? Columns can be mounted entirely above ground using wet set brackets.