Copper-Boron Groundline Treatment for Poles:
An Update on the Efficacy and Performance of a Copper Naphthenate-Borax Preservative Paste¹

By

T. L. Amburgey²
M. H. Freeman³

Abstract

A wood preservative paste consisting of borax and copper naphthenate has been tested to determine its efficacy and performance in protecting wood in ground contact from decay fungi and insects for a period of over 15 years. The paste was applied to polyethylene-backed wraps that were fastened to the below-ground portions of both seasoned and unseasoned southern pine pole stubs. After 4 years of exposure in Mississippi, in a high decay and high termite hazard zone, the untreated control stubs were completely deteriorated. After nearly 6 years of exposure, the groundline and below-ground portions of the treated stubs remained completely sound due to movement of copper and diffusion of the borate throughout the cross section. Borate and copper also moved vertically in the stubs and was present in sufficient amounts to protect sections of the stubs as high as 3 feet above grade.

After 9 years of exposure, the below-grade portions of the treated stubs had very limited areas of decay and no termite damage; the majority of the cross section remained sound. After 15.5 years, the pole stubs were removed from service and examined visually and measured for cross-sectional soundness. The visual inspection and push test on all treated stubs at 15.5 years indicated that all the stubs treated with the copper naphthenate-borax containing preservative paste were still serviceable. The cross-sectional areas near groundline, where attack had begun to extend from the uppermost untreated sections, had large percentages of solid, sound wood. This paper also reviews and summarizes previously published and unpublished work on copper naphthenate-boron treated wooden posts and results from other testing of remedially treated wood pole stubs.

An Update on the Efficacy and Performance of A Copper Naphthenate-Borax Preservative Paste

It is well-documented that failure in most adequately-treated southern pine poles occurs at or near the groundline and that supplemental treatments applied near this location can significantly increase the service life of poles (Edison Electric Institute 1959; Gjovik 1971, 1975; DeGroot 1981; Hayes 1986). While several formulations have been used either experimentally or commercially as groundline treatments, most topically-applied preservatives (remedial treatments) used in the United States have contained either pentachlorophenol or fluorides. This year, the manufacturers of pentachlorophenol will voluntarily remove groundline / remedial treatment applications from the U.S. EPA registered labels for the product, and penta use in groundline treatment will be prohibited.

Approximately 15.5 years ago, a field test with a copper naphthenate-borate paste (later named Cu-Rap 20™) for treating the groundline of poles was begun at the Mississippi State University Dorman Lake test site near Starkville, MS. It was hypothesized that such a formulation would combine the proven fungicidal effectiveness of copper-containing formulations with the fungicidal / insecticidal effectiveness of diffusible borate. Untreated southern pine pole stubs, either seasoned (air-dried) or non-seasoned (green), were treated on one end with either a gel containing pentachlorophenol (Pol-Nu™) or a paste containing copper naphthenate and borax (Cu-Rap 20™). The formulations then were covered with polyethylene that was stapled in place. The pole stubs then were placed in holes so that the wraps extended about two inches above ground. The upper ends of the pole stubs remained untreated and uncovered. Untreated stubs served as controls.

Pole stubs from each treatment group were periodically removed from the test site and sectioned both to determine their physical condition and to conduct chemical analysis. The condition of these stubs after varying periods of exposure was documented in several publications (Amburgey & West 1989, Amburgey & Freeman 1993a and 1993b, Freeman & Amburgey 1997 and Amburgey and Freeman 1997). The untreated controls could easily be broken after 4.5 years of exposure by leaning on them. The lower portions of all treated stubs were essentially free of insect and decay damage through the 9+ years inspection. The upper untreated portions of the stubs, however, experienced both decay and beetle damage. The stubs treated with Cu-Rap 20™ had less decay and fewer beetle exit holes than those treated with Pol-Nu™, but the Pol-Nu™ treated stubs remained sound at groundline. The effectiveness of Pol-Nu™ in this test confirms the results of other tests with this product (DeGroot 1981).

After 15.5 years of exposure, the groundline areas of most of the stubs had varying amounts of decay (Table 1), but none of them could be broken. The groundline area of one of the two remaining non-seasoned stubs that had been treated with Cu-Rap 20™ was completely sound (Table 1). The wood in the stubs treated with Cu-Rap 20™, especially those not seasoned before treatment, was protected from decay fungi and insects for over a foot above groundline.

Results with Cu-Rap 20™ treated stubs indicate that either the copper is being transported into the wood by the diffusible borate or that a diffusible copper/borate complex is formed within the wood. Other studies with this formulation indicate its effectiveness in protecting standing utility poles even in semi-arid environments (Freeman, Gross, & Manning 1994). Tests demonstrated that afterglow did not occur in CCA-treated pole stubs that had been groundline-treated with Cu-Rap 20™ (Amburgey & West 1989).

Tests in which unseasoned southern pine posts were diffusion-treated with the borate Timbor®, dried, and butt-treated with copper naphthenate also demonstrated the effectiveness of copper / borate treatments. While the borate eventually leached to below-threshold levels at the tops of the posts, the areas receiving both the copper and borate treatment (with no plastic wrap) remain sound after 10 years of exposure in Mississippi (Amburgey, unpublished).

Other tests with copper naphthenate-borax paste are ongoing as it continues to gain commercial use by both domestic and international utilities. Results of the other ongoing tests will be reported in future publications.

1. Approved for publication as Journal Article No. FP-162 of the Forest & Wildlife Research Center, Mississippi State University.
2. Professor, Forest Products Laboratory, Forest & Wildlife Research Center, Mississippi State University, Mississippi State, MS, 39762
3. Wood Scientist, 7421 Hunters Tree Cove, Memphis, TN, 38125

Literature Cited

1. Amburgey, T. L., M. West. 1989. Field tests with a groundline pole treatment. International Conference on Wood Poles and Piles, Fort Collins, Colorado, USA, October 25-27, 1989. pp. E1-E11.
2. Amburgey, T.L., M.H. Freeman. 1993a. Groundline treatments with a water-borne copper naphthenate-boron paste. In: Proc., 89th Annual Meeting of the American Wood-Preservers’ Assoc., Newport Beach, CA. May 2-5, 1993, 89:105.
3. Amburgey, T.L., M.H. Freeman. 1993b. Ten year field test with a copper-borate ground line treatment for poles. International Research Group on Wood Preservation, Document No. IRG/WP93-30017.
4. Amburgey, T.L., M.K. Freeman. 1997. Groundline treatments with a water-borne copper naphthenate-boron paste. In: Proc., 2nd Southeastern Pole Conference, MS State, MS. Jan 22-25, 1996. p. 157.
5. DeGroot, R.C. 1981. Groundline treatments of southern pine posts. USDA Forest Service, Forest Products Laboratory, Research Paper FPL 409. 9 pp.
6. Edison Electric Institute. 1959. Methods for inspection of standing wood poles in overhead lines. Edison Electric Institute, New York. Publication Number 59-74. 20 pp.
7. Freeman, M.H., R. Gross, & M. Manning. 1994. Laboratory and field performance of a copper-boron remedial treatment preservative paste. Proc., International Conference on Wood Poles and Piles, Fort Collins, Colorado, USA, March 20-23, 1994.
8. Freeman, M.H., T. L. Amburgey. 1997. Groundline treatments with a waterborne copper naphthenate-boron paste. In: Proc., Forest Products Society, 2nd International Conference on Wood Protection with Diffusible Preservatives and Pesticides. pp. 148.
9. Gjovik, L.R. 1971. Groundline preservative applications as supplemental treatments for standing poles. Proc., Fifth Wood Pole Institute, Colorado State Univ., Fort Collins, Colorado. pp. 20-34.
10. Gjovik, L.R. 1975. Evaluation of groundline preservative application for poles. Proc., Sixth Wood Pole Institute, Colorado State University, Fort Collins, Colorado. pp. 149-165.
11. Hayes, W.C. 1986. Extending wood pole life. Solving a $5-billion/program. Electrical World, Feb. 1986. pp. 41-47.

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