What Is Marine Plywood? Grades, Uses and Alternatives

Marine plywood is high-grade plywood made with waterproof, boil-proof glue and durable face and core veneers with no voids, usually to the British standard BS 1088 (okoume, meranti, sapele) or as Douglas fir marine grade. It does not delaminate when wet, which makes it the choice for boats, docks and outdoor furniture. It is not rot-proof: it still has to be sealed.

Marine plywood standards

Standard	What it means
BS 1088	The marine standard: durable species, WBP boil-proof glue, no core voids, limited face defects. Okoume, meranti, sapele.
BS 6566	A lower, cheaper marine-type grade; more defects allowed.
APA Marine (US)	Douglas fir or western larch with A or B veneers throughout, solid cores and exterior glue.
Lloyd’s Register	BS 1088 plywood tested and stamped by Lloyd’s: the highest assurance.

Marine vs exterior vs pressure-treated plywood

Plywood	Glue, core and use
Marine	Waterproof glue, void-free core, top veneers: boats and permanently wet places.
Exterior (e.g. AC, BC)	Waterproof glue but voids in the core: outdoor projects that dry out between rains.
Exposure 1 (CDX)	Glue that survives rain during construction, not permanent exposure: sheathing.
Pressure-treated	Chemically treated against rot and insects: ground contact, decks. Not for food contact or interiors.

Sizes and thicknesses

Marine plywood comes in 4 × 8 ft (1220 × 2440 mm) sheets, and 1250 × 2500 mm or 5 × 10 ft from some mills. Thicknesses run from 3 to 25 mm (1/8 to 1 in), with 6, 9, 12 and 18 mm the most common.

Advantages

Waterproof, boil-proof glue: it does not delaminate
No voids in the core, so no hidden weak spots
Strong and light for its stiffness
High-quality faces that take paint and epoxy well

Drawbacks

Much more expensive than exterior plywood
Not treated against rot: needs sealing or epoxy
Harder to find in small shops
Okoume faces are soft and dent easily

What it is used for

Boat hulls, decks and transoms
Docks and outdoor furniture
Bathroom, laundry and outdoor kitchen cabinets
Anything that will be wet often

Tips for working with Marine plywood

Seal every edge and face with epoxy or a good marine paint; the wood itself can still rot.
Use stainless or bronze screws outdoors.
For furniture that only sees rain, exterior plywood with sealed edges may be enough.
Check the stamp: BS 1088 marine plywood is certified; “marine-grade” alone may not be.

Frequently asked questions

Is marine plywood used for boat building?

Yes, that is what it is made for. Marine plywood for boat building (BS 1088 okoume or Douglas fir) has no core voids and waterproof glue, so it can be bent, glued and sealed with epoxy.