The Reason for External Treatment

While initial external preservative treatment provides excellent long term protection against fungal attack in a variety of environments, there are a number of service applications where the treatment eventually loses its effectiveness.  Soft rot fungi can then decay the wood surface, gradually reducing the effective circumference of the pole until replacement is necessary.  In these instances, pole service life can be markedly extended by periodic below ground application of external preservatives that eliminate fungi in the wood near the surface and provide a protective barrier against reinvasion by fungi in the surrounding soil.

For many years, the pastes used for this purpose incorporated a diverse mixture of chemicals including pentachlorophenol, potassium dichromate, creosote, fluoride and an array of insecticides.  The re-examination of pesticide registrations by the U.S. Environmental Protection Agency in the 1980’s resulted in several of these components being listed as restricted use pesticides.  This action, in turn encouraged utilities and chemical suppliers to examine alternative preservatives for this application.

Grease Type Products and Application

The use of grease type products by the very nature of its application does not permit you the opportunity to establish that the required amount of grease in the appropriate load rates has been applied. Grease products can be difficult to apply as they are either oil or water based. While they can be readily used to coat voids and checks, they are susceptible to ambient moisture and heat, making it difficult to get the appropriate load rates as required. Additionally, the binder that gives the product its body does not allow all of the preservative to be delivered to the pole as a portion of it is held in the binder. Traditionally, grease products have been tested by various credible institutions throughout North America. Virtually all tests have been conducted using a ¼ inch application as a basis for these tests. Application of a ¼ inch layer of a grease type product for a 36” diameter pole to cover 20 inches in depth at groundline protective area at ¼ inch depth requires 7.2 to 8.5 pounds of grease per pole. In some cases, the label on these products will tell you that a 1/16, 1/8 or ¼ inch can be applied. A 5 gallon (55lbs) pail should cover approximately 7.5 poles per pail when applied at ¼ inch coverage to provide for an approximate 10-year efficacy. Reduction in coverage equals a reduction in efficacy. Many contractors are treating substantially more poles, as many as 20 to 25 poles per pail.

Furthermore, application of the required product takes considerable time and is often not applied correctly due to the economics of the contract on behalf of the contractor. These low load rates are not sufficient for effective treatment. Moreover, the craft paper/butchers paper wrapped around the pole after the grease has been applied deteriorates rapidly thus allowing undesirable leaching of hazardous chemicals into the soil surrounding the pole. Consequently, this contaminates the soil/environment and robs the wood pole of the effective treatment chemical at the load rate necessary for effective treatment. As grease products are also highly corrosive, transporting or storing them can be restrictive.

Pillow Type Products and Application

The use of pillow type products offers a clean alternative to the application of treatment at the groundline areas as the product is contained in a polymetric pillow wrap. When the wrap is applied, workers are not directly exposed to the preservative. The design of the system also keeps environmental risks to a minimum.

Installation is relatively simple. The wrap is measured and cut to the appropriate length. The inner liner layer is either scored or peeled away from a perforated inner layer (dependent on the product) exposing the preservative layer. The wrap is then applied to the pole and stapled in place. The soil surrounding the structure will exert pressure that brings the preservative in universal contact with the pole surface. Installation time is minimal once the pole surfaces have been exposed. There is little danger of contact with either the applicator or the environment. After application, Quality Assurance (QA) is easily done to assure that a full and effective treatment has been performed. The design of the polymetric pillow affords a lasting reservoir of active ingredients applied to the pole surface as well as preventing the preservative from leaching out, which in turn prevents lessening of the treatment effectiveness and contamination of the surrounding soil. 

References: Oregon State University Utility Pole Research Cooperative Department of Wood Science & Engineering By: J.J. Morrell C. Freitag H. Chen C. Love;  Genics, Inc; Sciencelab.com; Preschem