If you need waterproof plywood for your construction project, as an experienced builder you need to be familiar with both exterior and marine plywood. While they may appear similar, these two types of plywood have significant differences that dictate their appropriate use.
To help you make an informed decision on which material to use, this article will list and compare the characteristics and applications of these two “waterproof” types of plywood.
What is marine plywood?
Marine plywood is a high-quality timber product composed of multiple layers of wood veneers bonded with water-resistant weather and boil proof (WBP) glue..
Many people consider marine grade plywood as one of the highest quality plywoods around. Marine plywood is known for its toughness, damage resistance, and ability to withstand extreme conditions.
It is made using naturally water-resistant tropical hardwood, arranging thinner plies for increased strength and compressing them with a special adhesive
This ensures that the resulting plywood doesn’t have any defects. It won’t have core gaps even when you cut the sheets. It also gives plywood its distinct toughness and damage resistance.
Plywood suppliers offer marine-grade plywood in several different grades. Each grade comes with a distinct knot size and frequency. Every one of them also has a unique weight and thickness.
- A-A
- A-B
- B-B
- Medium-density overlay (MDO)
- High-density overlay (HDO)
Uses
One of the most common uses of marine plywood is boat building. People use it to make different parts of the boat such as the hull. They take advantage of the plywood’s excellent pliability and water-resistant properties.
Marine plywood is not limited to seafaring, of course. Any portion of a house or building exterior can have plywood cladding made of these marine-grade boards. It is extremely useful for construction projects in areas that see lots of rain, moisture and/or fluctuations in temperature.
This is why we see marine-grade plywood in commercial settings. Restaurants and hotels use this plywood for their kitchens and bathrooms. benchtops and cabinets. It helps keep benchtops and cabinets waterproof.
Another example of marine plywood use is as a subfloor material. It prevents water and moisture from seeping through it, whether from the surface or below.
Other popular uses of marine grade plywood include:
- Docks
- Decks
- Patios
- Porches
What is exterior plywood?
Exterior plywood is the general term for weather-proof plywood primarily used for outdoor applications.
It is made from several layers of wood veneers bonded together using phenolic resin. The glue hardens to form a crystalline substance, making the plywood more resistant to moisture and humidity.
To make exterior plywood, manufacturers typically use wood from hoop pine. Other plywood materials include spruce, mahogany, Douglas fir, birch, oak and maple.
They treat the veneers with preservatives to make them more suitable for external use. This allows the plywood to withstand harsh weather conditions such as strong winds and heavy rain.
Similar to other plywood products, exterior plywood also comes in different ratings. Each grade represents the quality of the plywood sheet.
- A (cabinet grade)
- C-D (construction grade)
- X (suitable for outdoor use)
- C-D-X (most common grade)
Uses
Most builders use exterior plywood for non-structural, exterior applications. They take advantage of the plywood’s properties to create a high-quality aesthetic finish. Visit any building and you’ll likely see the plywood used for its outdoor walls and ceilings.
But this plywood type isn’t only limited to outdoor applications. Some builders have used this plywood in interior settings as well. These include storage and refrigerated areas.
Exterior plywood also works great as a subfloor. Its water-resistant nature doesn’t allow moisture to penetrate the floor whether from the surface or below.
Some other interior applications of this plywood include:
- Sinks
- Benchtops
- Kitchen cabinets
How is marine plywood different from exterior plywood?
One of the main differences between exterior and marine plywood is their use of adhesives.
Manufacturers use only permanent weather and boil proof glue to make marine plywood.
Meanwhile, they use other types of WBP glue for general exterior plywood.
Marine plywood standards also do not allow for any defects, even on its surface. This ensures that plywood remains water-resistant. On the other hand, exterior plywood allows for some defects. You can typically see this on C-D grade plywood.
The two plywood can differ in their thickness as well. You can find marine grade plywood with a veneer thickness of 1.3mm – 3.8mm for multi-ply construction. It’s also available in 0.5mm thickness for three-ply construction. Exterior plywood can come in reasonably thinner veneers to make them more affordable.
Finally, exterior and marine plywood differ in their species of wood. Manufacturers must use only high-density hardwood to produce marine plywood. Meanwhile, less stringent standards for other plywood allow them to use either high-density hardwood or mixed light hardwood.
How are the two plywoods similar?
Much of the similarities between exterior and marine plywood come in their uses.
To a certain extent, both exterior and marine plywood can be considered “waterproof plywood” and make excellent subfloor material. There’s no denying that both types of plywood can easily handle the wear and tear of daily use. Their water-resistant properties prevent moisture from passing through the subfloor and reaching the floor’s surface.
However, marine-grade plywood is manufactured to withstand more extreme conditions. While exterior plywood can survive harsh weather conditions like strong winds and heavy rain, it is marine-grade plywood that can withstand near-constant wet conditions longer. It is the material that boat makers can rely on to make their vessels hold up against the constant abuse of the sea.
Choose the appropriate “waterproof” plywood
As you have found out, exterior and marine plywood may look the same at first glance. However, they have quite a few characteristics that set them apart from each other.
Are you choosing between exterior or marine plywood for your next commercial project? Browse our article on how to choose between these.
Alternatively, feel free to contact FA Mitchell experts today for tailored advice. We’re the marine ply supplier who can help you choose the best product for your specific construction needs.
