24th August, 2020

Uses for Marine Plastic Lumber

Building marine structures presents a unique design challenge, as they must remain capable of supporting loads and withstanding impacts while also coming into constant contact with water. Oftentimes, construction companies’ go-to choices for building materials in marine contexts include wood and concrete supplemented by some metal and rubber. These materials can certainly get the job done, but they could also not be suited for every project. Wood can rot when it is wet, the solutes in seawater can erode concrete, metal may rust or may be too lightweight, and rubber may break apart over time. There is, however, another material you can turn to when you want to prioritize longevity without compromising strength – plastic lumber. We’ll describe its advantages and explore how to use marine plastic lumber so you can consider making use of it when it fits well with the needs of a future project.

The Beneficial Characteristics of Plastic Lumber

So, what makes plastic lumber advantageous in a variety of marine applications? Perhaps its greatest trait is that it is not prone to absorbing water and losing its structural integrity due to the substances naturally dissolved in seas. Plastic lumber is made of high-density polyethylene (HDPE), which is a type of plastic. It does not decay, can’t be eaten by marine borers, and it does not corrode, meaning that you can be sure it will last. Materials like metal and wood, on the other hand, may need relatively frequent maintenance to combat the effects of rust and rot.

A concern you may have with plastic lumber is that it is not robust enough to take on the physical force of water and weighty objects. While HDPE in itself can be somewhat malleable, manufacturers can fortify plastic lumber using either fiberglass strands or fiberglass polymer rebar, which runs through the length of a plastic lumber board. With this addition, builders have successfully constructed an array of marine structures using HDPE in the past.


Here are marine structures which may benefit from utilizing plastic lumber as a primary material.

Docks, Piers, and Decks

Travel to just about any large, public shoreline around the world and you will see docks or larger piers projecting out from the land into the water. There may also be decks to provide a nice elevated walkway above the ground. Traditionally, people envision such structures being held up and built with wood boards, but plastic lumber is another valid option to utilize.

Like wood, plastic lumber can be cut to the correct dimensions for surface boards laid on top of docks, piers, and decks. Plastic lumber can also form the substructures that make up the framework of these structures, as it will remain more unmoving than wood when put up against tides and winds when it contains fiberglass polymer rebar. Docks, piers, and decks built from plastic lumber do not need chemical treatments to seal and guard them against water and wood-eating organisms either. Finally, plastic lumber has resistance to UV radiation, so it will not discolor and chip when exposed to the sun. The structure you use it for will thus keep an attractive appearance for a long time.

Marine Plastic Lumber Fenders

Fenders are small fixtures that stick out from or stand in front of larger docks, piers, and bridges. Their purpose is to protect those structures from the bumping and abrasion of boats that people dock there. Therefore, they must have the ability to absorb and deflect impacts while also keeping themselves and the vessels that hit them undamaged. Wood and concrete are too rigid for this application, and rubber tends to work best on thick concrete structures that can support its weight and have solid faces near the water level.

With plastic lumber, you can form pile fenders that enclose dock or pier columns or form separate posts that surround the main structure. The latter variation is useful for directing boats away from the legs of bridges, where you want to minimize unnecessary strain for the safety of those passing above. Since those separately-standing fenders are anchored in the ground underwater, they moreover don’t require support from the dock or pier. Whether attached to existing structural columns or built apart, though, a plastic lumber composition imparts the fenders with a balanced blend of durability and helps to accomplish their purpose effectively.

Navigational Aids and Dolphin Clusters

Navigational aids and dolphin clusters are similar to fenders, but they distinguish themselves by the fact that they stand alone farther from larger structures in the water. This is because they serve more to guide the direction of traveling vessels as they approach the shore than to directly protect them. Navigational aids are posts that visually communicate where people can safely take their boats and often have brightly-colored signs attached to them. Dolphin clusters often exist in disconnected yet clear lines that create pathways for boats that are docking. People can also use them to secure their vessels by tying ropes around them.

Both navigational aids and dolphin cluster must withstand strong currents and the force of boats that collide with them. Once again, fiberglass-reinforced plastic lumber makes for the perfect material since it is stronger than wood and will not break down from organic processes even when it is constantly soaked.

Retaining Walls and Groynes

You can learn how to use marine plastic lumber for shoreline protection as well, as it’s possible to build retaining walls and groynes using the material. Retaining walls hold sediment and soil so they do not fall into the water and get washed away, while groynes stand in perpendicular lines relative to the shore so that erosion cannot occur in that direction. Both structures benefit when constructed from plastic lumber because of the material’s sturdiness and virtual immunity to the chemical changes that typically weaken wood, concrete, and other materials. They won’t sustain serious damage from the water even when it moves swiftly.

Seeing all these potential functions, you can start using plastic lumber for your marine projects by contacting Tangent Materials. Our commercial-grade structural lumber products, including our FiberForce®, BarForce®, SeaPile®, and SeaTimber® are all ideal for construction on coastlines. Call us today.