Tag Archives: CCA

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.

Dear Pole Barn Guru: Will Treated Wood Rot?

New!  The Pole Barn Guru’s mailbox is overflowing with questions.  Due to high demand, he is answering questions on Saturdays as well as Mondays.

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday or Saturday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

 DEAR POLE BARN GURU: I have a pole building reroofed with 1′ overhangs and am wondering if you think I should/need to use closures or something at the eave to seal the ribs. Thanks FREAKING IN FOSTORIA

DEAR FREAKING: I’d recommend the use of form fitted inside closures on top of the eave girt, if you have enclosed overhangs, or on top of the eave girt with open soffits. There should also be form fitted outside closures on top of the roof steel underneath the ridge cap.

This combination will help to keep those nasty little flying critters from joining you inside of your building.


 DEAR BUDDY: Not entirely sure how to best assist you from the two word question.

Assuming your new pole building is not going to be used as a home (in which case I would make entirely different recommendations using a raised wood floor), I’d approach this as for any pole building drainage solution. I would order columns long enough to get the required depth to extend below the frost line, plus make up for any grade change. After the columns were set, I’d bring in good compactable fill to get the elevation of the bottom of any future concrete slab above the highest point of the surrounding grade. Above the high side of the building, a French drain can be installed to divert any natural drainage.

For those who are unfamiliar with French drains, it is when a trench is dug beyond the building perimeter, drain rock is placed in the bottom, then one or more rows of perforated four inch pipe are laid. After placing the pipe, the balance of the trench is filled with drain rock. I hope this helps – if not…please email me more information.

DEAR POLE BARN GURU: My concern with ground contact treated wood is not environmental, it is by experience. Apparently, “treated” can be ambiguous as to what chemical, degree of saturation and retention level the wood has. I had the base of a support structure, in ground contact lumber, show some rot after about 12 years. The structure was on poorly drained soil and that may have been a contributing factor.

I was reading some ag forum topics on pole framed buildings with treated lumber bases and more than one contributor claimed failure at around 20 years, necessitating a restructuring of the foundation. That got me thinking about the concrete footing pillar but perhaps I am being a bit paranoid. MINDFUL IN MICHIGAN

DEAR MINDFUL: Sadly the treated wood, lumberyard and even the pole building industry have not done a very good job ensuring the end users of pressure preservative treated wood get the products which would do the job.

Most “ground contact” treated lumber is really not meant for any type of critical use applications.

I can say I have met or know every major pole barn builder and supplier in the United States, and I have yet to have had a report of any properly pressure preservative treated column ever rotting off. The key is “properly pressure treated”.

Here is an article I wrote earlier which will provide more in depth information:


MCA: Micronized Copper Technology

Particulate (micronized or dispersed) copper preservative technology has recently been introduced in the USA and Europe. In these systems, the copper is ground to micro sized particles and suspended in water rather than being dissolved in a chemical reaction as is the case with other copper products such as ACQ and Copper Azole. There are currently two particulate copper systems in production. One system uses a quat biocide system (known as MCQ) and is a take-off of ACQ. The other uses an azole biocide (known as MCA or μCA-C) and is a take-off of Copper Azole.

Treated Wood StampProponents of the particulate copper systems make the case the particulate copper system perform as well or better than the dissolved copper systems as a wood preservative, but other industry researchers disagree. None of the particulate copper systems have been submitted to the American Wood Protection Association (AWPA) for evaluation, thus the particulate systems should not be used in applications where AWPA standards are required. However, all of the particulate copper systems have been tested and approved for building code requirements by the International Code Council (ICC). The particulate copper systems provide a lighter color than dissolved copper systems such as ACQ or copper azole.

Proponents of the micronized copper systems claim the systems are subject to third party inspection under a quality monitor program. However, the monitoring program is not subject to oversight by the American Lumber Standards Committee (ALSC) as is required for the AWPA standard systems.

Two particulate copper systems, one marketed by Osmose as MicroPro and the other as Wolmanized using μCA-C formulation, have achieved Environmentally Preferable Product (EPP) certification. The EPP certification was issued by Scientific Certifications Systems (SCS), and is based on a comparative life-cycle impact assessments with an industry standard.

The copper particle size used in the “micronized” copper products ranges from 1 to 700 nm with an average under 300 nm. Larger particles (such as actual micron-scale particles) of copper do not adequately penetrate the wood cell walls. These micronized preservatives use nano particles of copper oxide, for which there are alleged safety concerns.

A competitor of Osmose, Viance, has waged what Osmose terms as a “negative public relations campaign questioning the effect”.

Osmose President Paul A. Goydan calls the campaign, “desperate, deceptive and damaging to the entire treated wood industry, including preservative manufacturers, wood treatment companies, distributors, retailers, contractors and deck builders.”

The chemical retention level of Micronized Copper is 0.23 lb/ft3 in order to meet the IBC (International Building Code) requirement of a UC-4B for structural in ground use in post frame buildings.

East of the Rocky Mountains, MCA has become the pressure treatment of choice for one of the large “box stores” as it requires no special fasteners (unlike ACQ treatments). ACQ treatments have been found to more quickly erode fasteners in contact with the treated lumber than the former CCA, and now….MCA.

Based upon the evidence at hand…although there is not a ten year or more history of MCA use, Osmose has obtained approval by the Building Codes for their product, and I’d not think one of the largest Big Box stores in America would endorse it’s use without close scrutiny.  At this point, I would have no reservations using MCA treated lumber in any building of my own.

Pressure Treated Lumber: Copper Azole

Most of us – both those who specify wood treating and those who use it, look upon the litany of possible wood treatments like alphabet soup.

Lumber Treatment PlantOr maybe more like Scrabble – where my 19 year old daughter always seems to either draw the right letters, or make otherwise incomprehensible words (to her Dad anyway) out of a total jumble.

Copper azole preservative (denoted as CA-B and CA-C under American Wood Protection Association/AWPA standards) is a major copper based wood preservative which has come into wide use in Canada, the USA, Europe, Japan and Australia following restrictions on CCA (Chromated Copper Arsenate). Its use is governed by national and international standards, which determine the volume of preservative uptake required for a specific timber end use.

Copper azole is similar to ACQ (Alkaline Copper Quaternary – read more at https://www.hansenpolebuildings.com/blog/2012/06/acq-treated-lumber/) with the difference being the dissolved copper preservative is augmented by an azole co-biocide like Tebuconazole instead of the quat biocide used in ACQ. The azole co-biocide yields a copper azole product which is effective at lower retentions than required for equivalent ACQ performance.

Here in North America it is marketed widely under the Wolmanized brand in North America.

The AWPA standard retention for CA-B is 0.10 lb/ft3 for above ground applications (UC-3) and 0.21 lb/ft3 (pounds of pressure treating chemical retained per cubic foot of wood) for ground contact applications (UC-4A). Type C copper azole, denoted as CA-C, has been introduced under the Wolmanized brand. The AWPA standard retention for CA-C is 0.06 lb/ft3 for above ground applications and 0.15 lb/ft3 for ground contact applications. Both CA-B and CA-C require a retention of 0.31 lb/ft3 in order to meet the IBC Code requirement of a UC-4B for structural in ground use in post frame buildings.

For detailed information on pressure treated lumber for structural in ground use: https://www.hansenpolebuildings.com/blog/2012/10/pressure-treated-posts-2/

The copper azole preservative incorporates organic triazoles such as tebuconazole or propiconazole as the co-biocide, which are also used to protect food crops. The general appearance of wood treated with copper azole preservative is similar to CCA with a green coloration.

Every piece of pressure treated lumber will have a tag on it stating what treatment chemical was used and to what level it was treated.  Be sure for look for these tags.  Don’t get fooled by companies stating they use wood treated for in ground use, only to be sent lumber with inadequate treatment.  Your future question to me will be “why did my posts rot?”  With the right chemicals, and the right level of treatment, your letter will have two words, “Thank You.”