Tag Archives: creosote

Protecting Posts from Rot

Protecting Posts From Rot

Based upon a Journal of Light Construction article by Grant Kirker, research forest products technologist at USDA’s Forest Products Laboratory in Madison, WI

Posts rot when decay fungi find wood they can digest. Insects such as subterranean termites can also cause posts to fail, but they aren’t common in cold climates, whereas fungi are widespread. Posts often rot at ground level and break off simply because this is where conditions are most conducive for decay to occur, as well as being where highest physical stress occurs. Here, fungi find those three basic things they need to grow and survive: moisture (from soil), oxygen (from air), and food (post itself).

While some wood species—such as eastern white cedar and black locust—are naturally resistant to decay fungi, their performance is highly dependent on extractive content in heartwood, and can be variable. Preservative treatment is a more controlled process resulting in more predictable performance, especially in soil contact. Wood preservatives have historically been formulated to be broad spectrum so they protect from a wide range of organisms. Most waterborne preservative systems commonly used today employ a metallic component (usually copper) combined with co-biocides to improve resistance to copper-tolerant fungi, molds, and bacteria. Our studies have found yellow-pine posts treated with several industrial wood preservatives (including CCA, ACA, pentachlorophenol, and creosote) have remained highly durable even after 50 years of field exposure in a harsh environment.

U.S. Forest Service Harrison Experimental Forest test plot in Saucier, Miss.—classified as a severe decay hazard according to AWPA’s Fungal Decay Hazard Map—is filled with longleaf-pine posts.

U.S. Forest Service A post is assessed by giving it a lateral pull of 50 pounds. If a post breaks at the ground line, it fails; if it doesn’t break, it passes. Tests have been conducted on these posts using this protocol since they were installed in 1964.

In order for a preservative to be effective, wood must be treated to proper retention level and penetration. If wood is treated only on the surface, any cracks or splits open up the treatment envelope and expose untreated wood, and can be readily eaten by fungi and insects. Some wood species (southern yellow pine, for example) are easy to treat and take up preservatives readily, while others (such as Douglas fir and lodge-pole pine) are more difficult to treat due to their wood cell orientation or heartwood presence. These species are often referred to as “refractory” and may require additional preparation (incising, steaming, and so on) to open up wood so it better accepts treatments.

When choosing wood for posts, check the end tag to confirm lumber is pressure-treated in accordance with either, American Wood Protection Association (AWPA), or International Code Commission (ICC). On the label, look for the product’s designated Use Category, or UC. The AWPA’s Use Category system specifies target retention levels for different preservative types to meet specific applications; UC 4B lumber (with a 0.60 pcf retention level for CCA, ACZA, and ACQ or 0.23 pcf for MCA) is required for harsh below-ground exposure in wet areas or regions with high decay hazard (like Southeast or Hawaii).

It’s not necessary to special-order heavy-duty marine-grade PT lumber. Marine pilings are typically treated to retention levels as high as 2.5 pcf CCA (chromated copper arsenate – generally no longer available for residential use) to ward off marine animals such as limnoria, teredo, and phloads, since some of these pests have been found to be copper tolerant. But for soil exposure, higher loadings aren’t necessary and just increase product cost.

U.S. Forest Service In addition to long-term industrial wood preservatives field testing, Forest Product Laboratory conducts research to develop new and improved treatment schedules for a variety of wood species. FPL’s state-of-the-art wood-treating pilot plant, constructed in 2010, offers five different preservative treatment retorts and can accommodate samples up to 12 feet long.

If you have to cut a PT post, be sure to dress any field cuts with a copper-naphthenate preservative containing at least 1% elemental copper. Examples include Copper-Green’s Wood Preservative (coppergreen.com), Tenino copper naphthenate (coppercare.com), and Woodlife Coppercoat (rustoleum.com). Cutting, drilling, or notching PT lumber exposes wood inner faces possibly not treated to the same retention as outer surfaces.

Some installers report wrapping post base with sheet copper or galvanized steel prolongs post life. While post wraps and barriers seem to offer some increased longevity, any gaps, holes, or voids behind the barrier or wrap will compromise the barrier and make it less useful. Coating post base with asphalt roofing cement, driveway sealer, tar, or a bituminous self-adhesive flashing tape are fairly common practices. In concept, these practices would seem to block some moisture transfer into wood, but there isn’t any research to suggest it increases longevity.

Finally, setting posts in concrete offers several advantages. First off, it reduces lateral post movement once it sets, making installation balance much easier. For square posts in foundations, it eliminates some shifting and settling. A recent European study evaluating concrete vs. gravel vs. dirt fill found concrete fill was a best option in regards to longevity and durability, but again, proper pressure treatment is key to long-term field performance. If fully encasing posts in concrete, be sure to bring concrete sleeve above grade and slope top surface away from post to shed water, as recommended in most local building codes.

Used Motor Oil for Treating Pole Barn Posts

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.