Buying Marine Plywood — What You Need to Know
Marine plywood is a specialty sheet good often used on boats and other outdoor applications. It differs from other plywood by the species of wood, number (and thickness) of layers, and the adhesive used in manufacturing.
Marine Plywood Core
Marine plywood is made up of many thin layers which reduces voids and large knots in the core. This helps prevent water infiltration and reduces the risk of rot and delamination. Additionally, marine plywood is manufactured with glue that is weather and boil proof (WBP). This means the glue can withstand a prolonged period of boiling without delaminating.
Marine Plywood Species
Marine plywood can be made from any species of wood that has rot resistant properties. It is commonly made from a tropical species of mahogany such as meranti or okoume.
Meranti: A wood species found in southeast Asia that has similar properties to genuine mahogany. It’s heavier than okoume and often used on the interior of boats.
Okoume: An African hardwood that is lightweight and bendable. For these reasons, it’s used on boat exteriors and finished with epoxy or fiberglass.
If the plywood is made of both meranti and okoume, it will be sold as mixed species.
Marine Plywood Grade
Plywood is graded by the quality (and appearance) of each face and uses an A – D scale (with A being the highest quality). Marine plywood is usually graded A/A or A/B. The first letter designates the grade for the top side, while the second letter designates the grade of the bottom side.
Grade A: Smooth, sanded surface without knots.
Grade B: Smooth, sanded surface. Face can have repaired defects (up to 1”).
BS 1088 is a British Standard specification for marine plywood. This designation is not limited to plywood produced in the UK — it can be used on any product manufactured that meets its standard. To meet this specification, the plywood must meet stringent requirements relating to adhesives, face, core veneers, manufacturing defect limitations, moisture content, finishing, size, and thickness. If the marine plywood has met the BS 1088 certification, the sheet will be stamped.
BS 6566 is another British Standard specification for marine plywood; however, it’s less stringent than BS 1088. The BS 6566 designation relaxes requirements around species and surface defects on the faces.
Did you know you have to finish marine plywood?
Marine plywood is water-resistant but will not withstand long-term water exposure without proper finishing. Epoxy, fiberglass, paint, varnish, or polyurethane are all acceptable finishes to protect plywood. All faces and edges need to be sealed to prevent moisture from penetrating the core.
At The WoodSource we stock meranti, okoume, mixed marine plywood in thicknesses varying from 4mm to 18mm. Stop by our showroom in Ottawa, or shop online from the comfort of your couch.
If you have questions about marine plywood or need help with a project, don’t hesitate to reach out to one of our knowledgeable sales staff.
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