For years, groups ranging from the U.S. Fish and Wildlife Service to the U.S Navy have tried to restrict the levels of oxygen getting to marine timber to extend the performance life of pilings. Until recently, pile wrapping provided the best solution. Although typically difficult and expensive to install, when used properly, wrapping was proven to decrease oxygen levels in treated areas and thus provide a longer life for the structure. However, wood expands and contracts. Seams loosen, and over time, fasteners fail. These actions result in easy entry for decomposers and a clear path for water flow, parallel to the grain, providing sustenance.

A study conducted by the Naval Civil Engineering Facilities reviewed the encasement of timber pilings before driving. "The Port of Tacoma used the former method in 1922 and the piling is still in excellent condition today."3 (at the time of publishing in 1987) Full encapsulation provides the benefits of wrapping to the entire pile and eliminates the weak points in the system.

Full encapsulation does not bond to the wooden core, allowing independent expansion and contraction inside the flexible membrane. This means the effectiveness of the seal does not rely on tension, which inevitably fluctuates, nor is the polymer protection susceptible to cracking during freeze thaw cycles. Full encapsulation eliminates seams and fasteners, which are the common failure points. Furthermore, the protected structural system is created as a single unit, in a state-of-the-art manufacturing facility, eliminating the need for on site installation, where quality control is difficult at best.

Full encapsulation provides the best defense against borers and other decomposers by limiting entry into the wooden core, and effectively suffocating whatever life may be within, through the restriction of oxygen and light.

Although remarkably durable, the polymer encapsulation may become gouged or nicked in extreme transportation or installation conditions (stabbed with a forklift, excavator, etc.). Although abusive conditions should be avoided whenever possible, and incidental damage repaired for aesthetic purposes, the bottom line is, even when left untreated, small holes and tears have a negligible effect on

performance. While organisms may gain minimal access to the wood, unless the tear exposes significant area parallel to the grain, sufficient water flow to provide enough oxygen to support life cannot typically be achieved

The Naval Civil Engineering Laboratory suggests "In.areas where repairs of chemically treated piling are soon required, it may be advisable to install prewrapped, treated bearing piling to avoid potentially catastrophic delays in wrapping."4 While the traditional wrapping of pressure treated wood is currently an acceptable option in many locations, it is not always a feasible solution, and is in most cases a temporary one. Prevention is always better than treatment in the field. The most effective method of limiting light and oxygen to timber, and thus significantly increasing the survival rate of structural timber in water is full encapsulation.

1. DEPARTMENTS OF THE ARMY,THE NAVY AND THE AIR FORCE "Maintenance of Waterfront Facilities" (Army TM 5-622, Navy MO-104, Air Force AFM 91-34)." June 1978: 2.1.1

2. Joseph Acosta, Andrew Cairns, Patrick King. Pile Wrap Evaluation Study Han-Padron Associates, LLP, New York, NY 10007

3, 4. D. Pendleton and T.O'Neill. Timber Piling Barrier and Chemical Preservation Annual Costs Comparison. (N-1773) NAVAL CIVIL ENGINEERING LABORATORY, PORT HUENEME, CALIFORNIA 93043. June 1987