Extending Wood Pole Life with Groundline Preservatives
For many years, pole owners have recognized the benefits of
inspection of in-service wood utility poles and service life extension through
the application of remedial treatments. However,
today's economic conditions combined with environmental issues, sustainability objectives, and ever-growing
regulatory mandates place an even greater burden on utility management to
maximize the safe use of their existing wood poles.
It's impossible to discuss effective remedial treatment programs
without an analysis of inspection methods and inspector qualifications. Suffice it to say that accurate inspection,
decay assessment, and treatment selection and application are equally as
important to the process, as the performance characteristics of remedial
treatment systems themselves.
treatments are designed to extend service life by supplementing the manufacturer's
original treatment. The depletion of the
pole's initial protective system happens over time and may be a result of aging,
weathering, migration, or the volatility of the chemical elements. Combined with the remaining original
preservative (typically pentachlorophenol, creosote, or CCA), remedial
treatments can provide an effective defense against a wide variety of wood-destroying
organisms, thus extending the useful service life many years beyond what is
typically expected (see Survivor Curve, Deterioration Zone 3 as referenced by
the American Wood Protection Association (AWPA) U1-12).
The All-Important Groundline
Wood poles commonly used in North America are subject to "shell rot" or surface
decay below the ground level. In
southern pine poles which compose roughly 85% of the poles in North America,
this type of decay is most common.
Western species such as Douglas fir and red cedar are less susceptible to
surface decay; however, the sapwood of neither Douglas fir nor western red
cedar is naturally resistant to decay.
Therefore, as these poles age they may be subject to surface decay,
though at later stages in life when compared to southern pine.
fungi are the most common wood-destroying organisms and they can be found in
virtually any environment. Decay fungi
require four elements in order to cause damage: air, water, a favorable
temperature, and food (in this case, the wood pole). These four elements are most prevalent from
the groundline to 18 inches below groundline (in most cases, air becomes a
limited factor at deeper depths). As a result, this area is highly susceptible
to decay. Since the outer two to three
inches of the pole is where approximately 90% of the strength is located, it is
vital to protect this part of the pole in order to preserve the pole's strength.
Preserving the durability of the pole plant can be
accomplished by in-place treatment with remedial preservatives as part of a
cyclical maintenance program. In
Bulletin 1730B-121, the Rural Utilities Service (RUS) recommends an 8 to 12
year cycle based on the decay conditions of the particular environment where
the poles are installed. Excluding
remedial treatments from a pole maintenance program leaves owners with an inspection
only program. This "run to failure"
strategy can have significant long-term negative impacts on our natural
resources, skilled manpower, financial resources, and it increases the pole
owner's risk with regard to safety and reliability.
Externally applied preservatives vary greatly in their chemical make-up, environmental
profile, efficacy, penetration into a pole, and their ability to remain in the
treatment zone so as to control decay for an extended period of time. Selecting
an appropriate remedial treatment strategy can save pole owner's millions of
dollars by reducing the number of pole change-outs and reducing the risks associated
with pole failures.
An effective external groundline treatment must have the
- The ability of one of the active ingredients to
penetrate the outer two to three inches of the pole, at or above threshold
levels. Additional active ingredients
can provide increased protection at or near the pole's surface. Note: The threshold level is the amount of
preservative that must be present in order to control decay.
- The active ingredients must display an ability
to remain in the designated treatment zone at levels capable of controlling
decay and for periods of time consistent with remedial treatment cycles.
- The active ingredients must be able to control
both soft rot and brown rot decay fungi.
- Remedial preservatives with multiple active
biocides are preferred as they can provide a broader spectrum of protection
against wood destroying organisms.
Active ingredients most commonly used in remedial groundline
treatments are various types of copper compounds (such as micronized copper carbonate and
copper hydroxide) and various types of borates. Groundline treatments vary in the way that
they are applied to the pole. Some are
available as a brush-on paste application which is then covered with a
polyethylene-backed moisture barrier to encourage inward migration of the
active ingredients. Others are available
as ready-to-use wrap applications - paste wraps, liquid wraps, and dry wraps. These wraps include the preservative and the
moisture barrier combined. Preservative systems can incorporate multiple active ingredients that serve different purposes. In these formulations, one active ingredient, such as boron, typically penetrates deeply while the other active ingredient, such as copper, typically stays closer to the surface. Preservative systems are found
to be much more effective than copper naphthenate alone because of copper
naphthenate's limited ability to penetrate wood at threshold levels in a
The majority of commercially available pastes are water-bourne and do not use
petroleum solvents or carriers. The
consistency of paste makes it easy to apply and helps ensure 100% coverage of the
pole surface in the treatment zone with no wasted product and no slumping (the
process of the product succumbing to gravity rather than remaining fixed in the
Bandages, though more expensive than pastes, are viewed by some as easier or
less-time consuming to apply, particularly dry bandages. However, with bandages there is the potential
for incomplete coverage of the targeted pole surface due to obstructions or
irregular surface resulting from decay removal.
A liquid bandage may be subjected to unequal distribution of material
because of the effect of gravity (slumping).
The seaming on segmented bandages can often limit coverage to less than
80% of the treatment zone and excess overlap can cause the preservative to be
directed away from the pole.
time to understand what remedial treatment options are available can have long-term
financial benefits. It can also limit
environmental exposure and other risks associated with pole ownership. Pole owner's Engineering, Standards, Risk
Management, and Environmental Departments are strongly encouraged to
investigate remedial treatment options as they plan their maintenance and sustainability strategies. Choosing a preservative that
will cover 100% of the treatment zone and penetrate and persist into the
desired pole depths is paramount to effectively preserving the useful service
life of wood poles. A preservative that
can accomplish those objectives and do so with a low toxicity profile and low
exposure risk is the ideal choice.