There have been a number of tests performed to date on barrier systems for wood preservation. These tests have proven that the use of barrier systems will significantly reduce the occurrence of decay and insect attack on treated and untreated wood posts. The barrier system also prevents depletion of wood preservative, which benefits post longevity performance and the environment.
Fungus Cellar/Soil Bed Test at Oregon State University On Booted and Non-Booted, Treated and Non-Treated Stakelets
In 1997, Oregon State University (OSU) researchers, T.C. Scheffer and J.J. Morrell, reported on a 2 year soil bed test where polyethylene boots were applied to both untreated and low retention treated stakes. Ponderosa pine was chosen for the stakes since its sapwood has low decay resistance. Flat stakes were used and saw kerfs on the entire length of both flat faces were made on some stakes to simulate seasoning checks. These kerfs increased the severity of the test. Half the stakes in the test were fitted with a 2-mil polyethylene boot before insertion of the stakes into the test soil. The remaining stakes had no boot. In addition to the completely untreated stakes, stakes with low retentions of either a minimal-leaching ground contact preservative, copper naphthenate, or a boron containing above ground preservative, disodium octaborate tetrahydrate were included.
The stakes were then inserted for 2 years in soil beds prepared from forest soil. This is the same methodology described in AWPA E14, Standard Method of the soil and “no attempt was made to keep water from entering the boots at the upper end”. At the end of the 2 year exposure, the stakes were removed and weighed to determine any losses.
The boots effectively prevented any attack, even on the untreated stakes. The booted stakes whether they were kerfed or nonkerfed had losses < 2% which the authors attributed to loss of extractives. The booted untreated stakes performed as well as the stakes with either of the preservative treatments. In comparison, the unbooted stakes showed evidence of attack in every group. Most of the stakes had weight losses of 10-40%. The best performing group in the unbooted series, the nonkerfed copper naphthenate group, had 3 of 10 stakes with an average weight loss of 30% while the remaining 4 averaged 2%. This could have been due to a localized instance of copper tolerant fungi or uneven preservative distribution. Regardless, it shows the effectiveness of the barrier in that none of the booted stakes showed any attack.
The authors of the Forest Products Journal publication conclude that:
“Booted stakes had little evidence of decay, whereas those without boots experience large weight loss and extreme shrinkage and deformation.”
Termite Tests at Mississippi State University
In 2000, termite resistance tests were conducted at Mississippi State University (MSU) on barrier wrapped wood in comparison to non-wrapped wood. The test was done according to AWPA Standard Method E-1, Standard Method for Laboratory Evaluation to Determine Resistance to Subterranean Termites.
For the “no choice” portion of the test, common subterranean termites (Reticulitermes spp.) were presented with a test specimen that was either wrapped or unwrapped. There was no other food source available in the test container and this is considered the more severe test for termite resistance. The results of the “no choice” were very convincing. There was no attack on any of the wrapped wood and all of the termites had starved to death at the end of the four week test. No detectable weight loss occurred for the wrapped samples in comparison to the 12-275 weight losses for the unwrapped wood. There was heavy attack and only slight termite mortality at the test end for the unwrapped controls. In this severe test, the barrier wrap clearly showed its termite resistance capabilities.
For the “two-choice” part of this test, both unwrapped and wrapped southern pine wafers are in the containers and the termites can choose a food source. Again, there was no attack on any of the wrapped wafers while the unwrapped ones had mostly heavy attack with some moderate attack. This test shows that the barrier system is repellant to termites and they will seek another food source if one is available.
The Prevention of Premature Failure of Preservative Treated Poles in Soil Contact
Albin A W Baecker – April 1998
“Pole Failure can be prevented if soil fungi are excluded from pole contact.”
“Field trials and installations of utility poles proved that “field liners” or barrier systems” prevented access of decay fungi to poles.”
“Preservative-treated wooden utility poles are normally required to last for 30 years in soil-contact, but it is well known that premature failure of such poles can and does occur.”
“Since the pole was preserved, how has it failed after only a few years in service? Some people deny that the question is worth asking. Unfortunately, the answer is not so simple, and the causes of premature pole failure have baffled experts for decades. What is know for sure however is that the failure is actually caused by fungal and bacterial decay and in some cases by insects such as subterranean termites. How these organisms overcome the toxic effects of wood preservatives remains a mystery. All that consumers can do to offset the effects of pole decay organisms is to employ regular inspection services to try to detect the early stages of decay in the poles and if decay is found early enough, the pole may be saved for another few years by remedial treatment involving the on-site application of more preservatives to the standing pole.”
“We are biotechnologists specializing in wood decay. Knowing that the causes of premature failure are not fully understood, we approached this problem with the certain knowledge that the fungi, which cause poles to decay, need (4) main things to grow. These are oxygen, water, nutrients and time to cause the decay.”
“As biotechnologists, we knew that if any one of the above growth factors is missing, fungi couldn’t grow. The lack of it is a hurdle, which the fungus has to overcome in order to rot a substrate. One of the growth factors is actually deficient in a pole, the nutrient nitrogen. So how can a pole rot? Well, while we knew that nitrogen is present in the surrounding soil, we also knew that soil fungi will transport this nutrient into wood to set the carbon : nitrogen balance at the level needed for the fungi to decay the wood.”
“Preservatives are designed to prevent decay of in-service utility poles, but treated poles fail prematurely through insect and fungal attack. This attack occurs where preservative is lost to soil.
“In complete contrast, the “field liner/barrier system” is a biotechnological device which prevents insect and fungal attack, while simultaneously acting as an environmental barrier which confines the preservative to the pole.”
“Their environmental benefits include conservation of poles and thus forests conservation of preservatives and thus energy, as well as accident prevention. They prevent pollution of soil, plant roots, and water. Field liner/barrier systems benefits include saving on pole inspection costs, pole replacement costs, and reduced preservation costs through use of lower retentions.”
Using Physical Barriers to Prevent In-Ground Wooden Pole Decay: Protecting Forest and Economic Resources as well as Soil and Groundwater
By Dr. Alan R. Howgrave-Graham, Dr. Laurie J. Cookson and Dr. Andrew Percy.
Published by The Sustainability Collection
Wooden poles and posts have been used for decades as the cheapest and most convenient way to carry electricity, telephone lines, build fences and vineyard trellises. However, a multitude of soil organisms can decay wood, requiring regular replacement of decayed poles and posts. Preservatives such as creosote or CCA are currently used to impregnate timber and extend its in-soil life but these may be environmentally detrimental as leaching can contaminate soil and groundwater. A preserved wooden utility pole should last 25 years in soil before replacement with a concrete, steel or another preserved wooden pole. A physical barrier, a field liner (FL), has been used to encase the base of posts to retain preservative while preventing soil-to-post contact.
This paper reports on a 26 month accelerated field trial (equivalent to 5.42 years under normal conditions) testing FL’s fitted to lightly preserved (ACQ) and unpreserved posts in Australia. The field liners were calculated to be successful at extending the in-ground life of untreated posts 3.6 fold. Nearly all the sapwood of untreated posts without FL’s had rotted within 26 months, while the sapwood of lightly preserved posts without FL’s are expected to last 35 months in the trial (equivalent to 7.3 years in the field).
No decay was found after 26 months with the lightly preserved posts with FL’s. These barriers were thus shown to confer considerable protection on wooden posts (whether preserved or unpreserved) from woodrot fungi in soil. This paper explains (with some quantitative data and modelling as evidence) the significance of this finding in terms of: reduced demand on timber supplies in Australia (in terms of both plantation and old-growth forests); cost saving to the utility companies; and the impact that using FL’s would have on protecting soil and groundwater from preservative leaching.