There are several distinctions between marine plywood and lower-grading plywood. If you aren’t aware of these, you can end up using the wrong kind and destroy the integrity of a project.
With that in mind, I’ll everything you need to know about marine plywood grades to avoid spending money on the wrong kind of lumber!
What is Marine-Grade Plywood and Where it is Made From?
It is plywood used in marine construction or boat building is of the finest quality. Marine-grade materials must be completely waterproof and withstand repeated exposure to snow and rain. However, this is not the sole need to be classified as marine grade.
Cornelius Bruynzeel, a Dutch door manufacturer, developed marine quality material in the 1930s. It was utilized to construct boat parts in the armed forces throughout world war II.
Only Douglas Fir or Western Larch is suitable for making marine-grade sheets. There should be five layers, and voids and air pockets should be less than in normal plywood.
Certain knots in the outer plies are okay, but knotholes are not.
5 Grades of Marine Plywood
A High-Density Overlay is a more robust forming layer that is more stable, smoother, and impervious to outside contaminants.
A medium-density overlay is an exterior plywood manufactured using hot temperatures and pressure to establish a first-rate thermosetting fiber overlay impregnated with resin.
Interesting Read: Exterior Plywood Grades and Its Uses
B-B grade or Face-back Marine plywood has a consistent, pale hue and is deemed clear due to its lack of flaws.
A-B grade is heavier and stronger than A-A and exterior-grade plywood and is available in the same width and length but is three-quarters of an inch thick.
The standard sizes for this grade of plywood are 4′ x 8′ and 5′ x 12′, and the thickness ranges from 0.5 to 1.5 inches.
Features of Marine Plywood: What Makes it Special?
Laminated and Lawyered Exterior
Thin sheets of veneer are placed perpendicularly atop, adding strength to the sheet.
Cross-lamination describes the manufacturing method that provides plies its exceptional durability. A marine-grade plywood panel is held together securely at both ends, making assembly simpler and more reliable.
The glue treatment is responsible for its water-tightness. Waterproof glue, often a resorcinol-type glue clear epoxy, is used to heat-bond the layers under pressure.
When dry, it forms a durable coating that resists the damaging effects of moisture, high temperatures, and high humidity.
Poreless Wood Surface
Laminating and sanding the surface layers is a step in preparing it for use.
Along with cross-lamination, this method eliminates the possibility of water leaking through the panel’s layers by sealing off all holes and air pockets at both ends.
Where to Use Marine Grade Plywood (Patios, Outdoor Furniture, and More)
When it comes to figuring out where marine-grade plywood truly shines, I’ve found it to be a versatile choice for various outdoor projects. You can put it to work for decking, garden furniture, planters, chairs, porches, benches, pergolas, and even arbors – the possibilities are abundant.
Although it is ideal for furniture construction, you must seal it thoroughly to prevent moisture damage.
Marine Grade Plywood Installation
Plywood marine-grade panels indeed have a wide range of applications. In general, you may lay it the same way you would lay down any other wood. However, the specifics of where and how you can install it will vary.
Marine-Grade Plywood and Sheathing Comparison
A marine-grade sheet is distinguished from other varieties of plywood by its superior quantity of veneers, adhesive, and veneer quality.
Ply panels used for sheathing typically have fewer thicker layers than that used for construction.
When a normal panel is ripped open, flaws like voids and bigger knots in the sheet’s inner veneers become apparent.
Water can seep into unfilled edge gaps, causing rotting or delamination, so it’s important to seal them off. In contrast, it has several thinner layers and no major knots or voids.
While the strength of the panels is achieved by the alternating position of veneers in every sheet, the durability and better fastener retention of Marine Grade panels come from the use of additional and full-face veneers.
Marine Grade Plywood and Regular Plywood Comparison: 7 Factors
Marine panels have a natural advantage because it is constructed from dense and thick hardwood species.
When stacked, they create an impenetrable barrier against water and moisture because of the finer grains that constitute the panel. When used to build boats, it guarantees that the structure will hold up in even the worst weather and can support more weight on the inside.
However, softwoods like pine are used to make standard panels. Due to its naturally bigger wood grains, this type of wood is not appropriate for marine uses, while you may utilize it in other residential construction projects.
Wood Exterior and Layers
You can distinguish the two varieties of ply sheets from each other with a glance.
Marine panels have a superior appearance since their exterior is smooth and polished. The lamination process, particularly the last coat of waterproof adhesive applied to the veneers, has a role in this.
The smooth surface is not only aesthetically beautiful; it also acts as a barrier against water, preventing it from seeping into the wood and causing it to slide away. Since wood stretches and shrinks without cracking the paint, it is much simpler to paint.
The chemical procedure and absence of a laminated surface give standard plywood a rough outer surface.
When talking about the lifespan of marine panels, it’s a fascinating mix of longevity and durability in my experience. With the right care and consideration of the marine environment’s challenges, these panels can impressively last up to 25 years.
Durable layers make it scratch- and impact-proof, contributing to its increased durability. It is resistant to heat, so it won’t suffer the same kind of wear and tear that other boats do over time.
On the flip side, I’ve observed that regular plywood doesn’t quite measure up. It tends to deteriorate rather swiftly, sometimes within just a few years, making it a less-than-ideal choice for applications that demand lasting quality.
Both A and B types are considered marine panels and meet the standards set by the Engineered Wood Association. They are both of the highest quality necessary for use aboard ships. Having fewer knots and other obvious flaws contributes to higher grading for panels.
However, you can find regular panels in gradings as low as D. This rating indicates the panel’s entire quality, including its structural integrity and longevity, not only its obvious flaws. This low-quality level is unacceptable in the maritime building.
Rot and Decay Resistance
Marine-grade types of plywood are not chemically manufactured but are pressure treated through a process that includes gluing and cross-lamination.
Avoiding potentially harmful chemicals helps it keep its sleek appearance and maintains its inherent resistance to moisture, which delays the onset of rot and disintegration.
But regular panels have a natural resistance to water and heat diminished by chemical treatments to make them survive longer.
Chemicals like copper and arsenic are employed, and they both have a toxic effect on marine life when left submerged for extended periods.
Despite appearing heavy and substantial, it is quite light and bendable. Cutting and bending may be shaped in several ways without damaging its integrity.
Due to its flexibility, it is resistant to scratches and won’t break or bend even when subjected to rough seas. This trait also means that it is a great option for the do-it-yourself boat builder, as it is lightweight and resistant to denting from accidental drops.
However, regular plywood grades has a stiffer composition, which is more challenging to trim and twist and much heavier to move.
Other Strong Alternatives
Ipe, cypress, cedar, shorea,  and redwood are some naturally decay-resistant wood species that are less likely to rot from molds and other species that feast on lumber.
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Similar to pressure-treated lumber and plywood, marine plies are not treated to prevent rot. That means if you’re planning to use them in a wet environment, you’ll want to take an extra step. Applying a reliable coating that’s resistant to water infiltration is a must before putting marine plies to work in these conditions.
I recommend going with pressure-treated timber or plywood graded for the anticipated degree of exposure if you require a component that can withstand dampness without a protective coating.
Marine-Grade Plywood Pricing
Top Suppliers of Marine Grade Plywood
In addition to other types of plywood, Cal Panel now offers Marine grade plywood for sale. They carry an extensive selection of goods that qualify as “green” or help get LEED points.
Marine-grade plywood is just one of the many wood species that Chesapeake Plywood distributes wholesale. Furthermore, they can facilitate exports to foreign clients.
On Amazon, you can shop from many categories and have everything shipped right to your door. With its vast inventory and convenient online platform, Amazon offers a wide range of high-quality plywood.
A major perk is an option to browse reviews written by other Amazon shoppers about the same plywood you’re considering purchasing.
Plywood Company, with headquarters in the Dallas-Fort Worth metroplex, is a major supplier of plywood of varying gradings, including Marine grade plywood. Since 2008, the Plywood Company has held the FSC seal of approval.
Recommended Marine-Grade Plywood To Use
Okoume Marine Plywood
Plywood made from Bruynzeel Okoume Gaboon (Aucoumea klaineana) is another great option other than Douglas Fir for usage in boats and harsh climates because of its BS 1088 rating.
Douglas Fir Marine Grade Plywood
A marine sheet made from Douglas Fir is sturdy, flexible, and lightweight. There may be up to five repairs or patches on the faces, but there will be no voids, making this face veneer the least expensive alternative for maritime plywood.
Marine plywood grades are some of the most important factors in finding the best material to make it through rough seas if you plan on building boats.
You may rest assured that it will survive for many years with minimal upkeep thanks to its sturdy construction. It has the necessary water resistance and strength for marine applications.
Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.
Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.