Is Marine Plywood Fully Waterproof? | Expert Guide from Plywood Etc

Marine plywood is one of the most popular sheet materials for outdoor and wet-area projects—but many customers still ask the same questions: Is it fully waterproof? Does it need sealing? How long will it last outside?

At Plywood Etc, a sheet materials specialist based in Leicester, we supply marine plywood in full-size and handy-sized sheets, as well as cut-to-size solutions for bulk requirements across Leicestershire, Nottingham, Derby, Coventry, and Rugby. This guide answers the most common questions we hear from trade and DIY customers.

Is Marine Plywood Fully Waterproof?

Marine plywood is not completely waterproof, but it is highly water resistant.

Marine ply is manufactured using:

• Waterproof phenolic resin glue

• High-quality hardwood veneers

• Void-free construction to prevent internal water traps

This makes it significantly more moisture resistant than standard plywood. However, the timber itself can still absorb water, particularly through exposed edges and unsealed surfaces.

For outdoor projects in the UK climate—especially around Leicester and the East Midlands—marine plywood should always be protected with a suitable finish.

Is It Okay for Marine Plywood to Get Wet?

Yes, marine plywood can get wet without immediate damage.

It is designed to cope with:

• Rain exposure during construction

• High humidity

• Splashing and intermittent moisture

However, it is not intended for continuous submersion or long-term exposure without protection. Allowing the boards to dry properly between wet periods is key to long-term performance.

Does Marine Plywood Need to Be Sealed?

Yes—marine plywood should always be sealed for outdoor use.

Sealing marine ply:

• Reduces moisture absorption

• Prevents swelling, splitting, and delamination

• Protects against rot and mould

• Extends the lifespan significantly

This is especially important for projects across Leicestershire, Nottinghamshire, and Warwickshire, where fluctuating weather can cause repeated wet–dry cycles.

What Is the Best Protection for Marine Plywood?

For maximum durability in outdoor conditions, we recommend the following protection methods:

Epoxy Resin (Best Overall Protection)

• Creates a waterproof barrier

• Ideal for marine use, outdoor furniture, and exposed structures

• Should be finished with UV-resistant paint or varnish

Exterior or Marine Paint

• Provides strong water and UV resistance

• Easier to maintain than epoxy

• Suitable for sheds, decking, and outdoor joinery

Marine Varnish or Exterior Oil

• Preserves a natural timber appearance

• Requires periodic reapplication

• Best for decorative outdoor applications

👉 Important: Always seal all edges thoroughly—edges absorb moisture faster than faces.

How Long Will Marine Plywood Last Outside?

When correctly sealed and maintained, marine plywood can last:

• 15–25 years outdoors

• 25+ years in sheltered or protected environments

Unsealed marine plywood used outdoors may deteriorate within just a few years, even though it is marine grade.

Common Marine Plywood Thicknesses (mm)

At Plywood Etc, marine plywood is commonly supplied in the following thicknesses:

• 6mm – Lightweight panels, linings

• 9mm – Interior joinery, cabinetry

• 12mm – Flooring, furniture

• 15mm – Structural panels, outdoor furniture, decking

• 18mm – Heavy-duty flooring and benches

• 25mm – High-load structural applications

✔ 15mm marine plywood is one of the most popular choices for outdoor and construction projects across Leicester and the Midlands.

Marine Plywood Supplied by Plywood Etc, Leicester

As a Leicester-based sheet materials specialist, Plywood Etc supplies:

• Full size sheets

• Handy sized sheets for DIY projects

• Cut-to-size marine plywood for bulk and trade requirements

We supply customers throughout Leicester, Leicestershire, Nottingham, Derby, Coventry, and Rugby, offering reliable stock, accurate cutting, and knowledgeable advice.

Is Marine Plywood the Right Choice for Your Project?

✔ Highly water resistant
✔ Strong and durable
✔ Ideal for outdoor and wet environments
✔ Suitable for trade and DIY use

❗ Requires sealing for long-term outdoor performance

If you need help choosing the right marine plywood thickness, size, or finish, the team at Plywood Etc is always happy to help.