What problems can affect wooden structures?
The above photograph illustrates the devastating effect that marine borers can have on wooden marine structures.
While wood is not affected by corrosion as defined and discussed above, wood structures are subject to unique damage in the marine environment.
The Problem of Marine Borers
Of greatest concern are organisms collectively referred to as marine borers. Once a marine borer has infiltrated an untreated marine piling, it is only a matter of time before the entire structure will become infested, weaken, and collapse.
Although hundreds of marine borers exist, three are quite common in the northeastern United States: Teredo navalis, Bankia gouldi, and Limnoria lignorum.
Teredo Navalis
Teredo navalis is a marine bivalve mollusk. Its two shells, enclosing only the front end of the body, function as a tool - their ridged and roughened surfaces are used for boring.
These borers often resemble a worm and may grow up to 2 feet long, although its shells remain only 1/2 inch long. Like other marine borers, Teredo navalis feeds on wood particles and minute organisms.
Bankia Gouldi
Also a mollusk, Bankia gouldi is a native species and was first identified from specimens found in Norfolk Harbor in Norfolk, Virginia. Bankia gouldi can survive and even thrive in salinities far lower than those tolerated by Teredo navalis, can withstand harsh winter conditions, and is just as devastating to marine structures.
Limnoria Lignorum
Lastly, Limnoria lignorum, commonly referred to as a “gribble,” causes a tremendous amount of damage and is far more conspicuous than many other marine borers. Limnoria lignorum differs from Teredo navalis and Bankia gouldi, however, in that it is an isopod, not a mollusk.
According to recent estimates, Teredo navalis alone is responsible for over $200 million dollars in annual damages to wooden structures in the United States, while annual damage in the U.S. from all species of marine borers reaches into the billions of dollars.
What Can Be Done to Prevent This?
One traditional method to prevent marine borer infestation was to use creosote-impregnated pilings. However, in this era of greater environmental consciousness, many states have prohibited the use of creosote as well as numerous other pile treatment chemicals.
Some newer, environmentally sound chemical treatments are available for new construction, and for older installations a variety of wraps or encapsulations exist. Even in the case of new construction, serious consideration should be given to an appropriate wrap or encapsulation process to extend the life of the structure.
Marine borer infestation can certainly be controlled or altogether eliminated, but each situation and location is unique and may call for a different approach.