According to The U.S. Army Corps of Engineers, The Air Force Civil Engineer Support Agency, and the Naval Facilities Engineering Command, "Timber structures in a marine environment are subject to attack by a variety of destructive organisms. Thus, they should be properly treated with appropriate preservatives to prevent or retard this type of deterioration."1

In aquatic environments, timbers and pilings, like any organic bodies, are destroyed through decomposition by fungus, bacteria, termites, and other aquatic invertebrates known as marine borers - with consequences that range from mild cosmetic damage to a complete loss of structural integrity.

The demand to increase the lifespan of structural timber has created a multi-billion dollar industry in wood preservation. New preservation methods are constantly being developed and perfected. While the problems and solutions associated with wood deterioration are simple in nature, the most effective preventative processes are more complex. This paper will outline these preventative processes that happen behind the scenes when using encapsulated marine piling.

Since ancient times there has been significant research and development into timber preservation methods. Today, there are three basic types; chemical treatment, pile wrapping, and full encapsulation. The first major breakthrough in wood preservation was treatment with chemical preservatives or pesticides. This method has been implemented in many forms for thousands of years and is still the most widely used type of preservative treatment. Today, chromated copper arsenate (CCA) is the most common pesticide applied to wood for marine use. While this treatment is generally effective against land-born decomposers, it is generally ineffective at combating marine borers. Additionally, CCA is water-soluble and will leach when in direct contact with water, leaving the wood exposed to attack and depositing potentially toxic chemicals to the environment. Like the pesticide creosote, (which was banned by many agencies including the European Union) CCA is beginning to see more and more restrictions in marine and residential applications by the EPA and similar organizations due to possible chemical contamination.

A second technique, known as pile wrapping (typically used in conjunction with pressure treated wood), has seen increased use over the last several decades. Wrapping has been shown to be an effective supplemental preservation method against marine borers but requires chemical

treatment to work effectively against all the major wood destroying organisms. Pile wrapping involves wrapping exposed pile sections with an impervious flexible plastic wrap. This technique is focused primarily on limiting marine borer damage after it has already begun. Additionally, the numerous seams and failure points involved in this method leave much to be desired in providing long term preservation.

In their pile wrap evaluation study, Han-Padron Associates concluded the following. "As was the case in this study, the bands that are needed to ensure a good seal can corrode and fall off. This can cause an effectively functioning wrap to fail."2

Full encapsulation currently offers the most effective solution to wood decomposition and structural loss. This approach builds on the proven process of conventional pile wrapping and pressure treatment, but virtually eliminates each of their inherent weak points, e.g., staples, nails, banding, seams, and chemical leaching.

This new technology allows a continuous polymer sleeve to seamlessly encapsulate a structural wooden core.

To best understand how to prevent timber deterioration, a look at natural occurrences that lead to the desired result will provide some insight. Fish and other aquatic organisms can die in periods of high cloud cover and low winds. A similar result occurs in a phenomenon known as winterkill, which occurs when ice and snow blanket a body of water. Both of these scenarios create environments unsuitable to sustain aquatic life.

From human beings, to worms, to bacteria, organism survival is heavily dependant on oxygen. In addition to organic matter for food, virtually all decomposers require oxygen for survival. These organisms typically separate dissolved oxygen

from the water through gills or other breathing apparatuses.

Most of this dissolved oxygen comes from the atmosphere. After dissolving at the surface, oxygen is distributed by current and turbulence. Algae and other aquatic plants also deliver oxygen to the water through photosynthesis.

Because of the contact with the atmosphere and amount of available light, the highest concentration of dissolved oxygen is located at the surface of the water. This level varies linearly with depth, so the more shallow the water, the more habitable the environment for unwanted pests. This is unfortunate for most wooden marine structures, which are typically located in relatively shallow waters.

After finding a suitable piece of wood, marine borers and many bacteria burrow into, consume, and decompose the wood, traveling parallel to the grain. This leaves a nice path for water to flow, replacing the old, oxygen deprived water with new oxygen rich water.

With an established line of oxygen replenishment, these unwanted organisms can enjoy a nutrient rich environment while causing significant cross-sectional damage to the structure. In addition to replenishment by new water circulation, oxygen can be generated locally by photosynthesizing organisms, which feed on light and decomposed material. Requiring only the additional presence of light, a self-supporting symbiotic relationship is formed between the decomposer and photosynthesizer, in which each supports the others' life until no consumable wood remains.

By sufficiently restricting the water circulation and available light, virtually no marine decomposers can survive.

Damage prevention from wood decomposition is a two tiered process:

1. Prevent or deter unwanted decomposers from entering the wood.
2. Create a habitat in which no organism can survive, discouraging those that gain entry and those that existed beforehand.

The most effective way to achieve the first step is simply to block organisms' access to the wood. At first glance, it would appear that the primary function of full encapsulation is to accomplish this goal. While it is highly effective in this way, a much more formidable operation is achieved. The second, but more effective preventative measure, involves restricting the oxygen that most decomposers need to survive.