Is marine grade plywood waterproof?

It is highly moisture-resistant due to Type I adhesive, but it is not impervious to water over long-term total submersion without protective sealing.

What is the difference between marine grade and pressure-treated plywood?

Marine grade focuses on wood quality and void-free construction; pressure-treated focuses on chemical treatment to prevent rot in direct soil or water contact.

Does marine plywood require painting?

Yes, it should be finished with exterior-grade paint, varnish, or epoxy to protect the wood fibers and seal the edges.

Can I use marine plywood for subfloors?

Yes, it is excellent for subflooring in high-humidity areas, provided the joist spacing meets the panel span rating.

Marine Grade PlywoodGenerating image…

Plywood & Sheathing

Panels

$110 to $220 per 4x8 sheet (2026 average market estimates for 3/4 inch marine grade).

Marine Grade Plywood Technical Reference (2026)

Prepared by Lumberama's Building Materials Team

|Last updated September 3, 2026|Sources & methodology

Marine grade plywood is a high-quality hardwood panel manufactured using water-resistant structural adhesives and veneers free from voids. Unlike standard exterior plywood, marine grade panels are engineered to withstand prolonged exposure to moisture, high humidity, and direct water contact through the use of high-grade Douglas fir or Western larch face and inner plies.

Key Features

APA-rated Exterior Exposure 1 or Marine Grade classification. - Waterproof structural bond (Type I glue). - Face and back veneers are typically B-grade or better. - Core veneers are free of knots and surface defects. - Resists delamination under extreme moisture cycles.

Specifications

Common Thicknesses: 1/4 inch

3/8 inch

1/2 inch

5/8 inch

3/4 inch. - Standard Panel Size: 4 ft x 8 ft. - Adhesive: Phenol-formaldehyde resin. - Grades: A-A

A-B

B-B Marine Grade. - Performance Standard: PS 1-09.

Applications

Boat hull construction and interior marine cabinetry. - Exterior docks and piers. - Subflooring in high-moisture environments. - Kitchen and bathroom wet-area cabinetry. - Siding and outdoor signage.

Installation Overview

- Ensure face grain runs perpendicular to supports for maximum strength. - Use stainless steel or high-quality hot-dipped galvanized fasteners to prevent corrosion. - Seal all cut edges with an epoxy or exterior-grade sealant to prevent moisture wicking. - Maintain a 1/8-inch gap between panels for thermal expansion.

Pros & Cons

Pros

✓ Extremely durable against moisture. - Consistent void-free core structure. - High structural integrity under load. - Excellent surface for marine-grade paint or varnish.

Cons

✗ Significantly higher cost than standard exterior plywood. - Heavy weight compared to non-marine alternatives. - Requires specific finishing to maintain long-term integrity.

Code Requirements

- Must meet PS 1-09 standards for structural plywood. - Check local municipal code for wet-room or exterior assembly requirements. - Consult APA (The Engineered Wood Association) grade stamps to verify exposure ratings.

Buying Tips

- Verify the APA grade stamp on the panel edge. - Inspect for 'Marine' designation specifically, not just 'Exterior'. - Check for surface cracks or overlaps in the top veneer. - Verify the panel thickness meets your project’s span requirements.