Sourcing quality hardwood plywood is difficult enough; when you get into marine-grade plywood, defining terms and determining quality can be even more significant. Throughout the lumber industry, the term “marine grade” can be used by manufacturers to mean a variety of things. Like many terms, you probably need to be a little more specific about your application and expectations than simply using that somewhat broad term.
To help equip you to have that kind of clarifying conversation, we’ll take a peek at some of the things which manufacturers as well as customers might mean when they talk about “marine plywood.”
While some terms or grades are extremely clearly defined by the Engineered Wood Association, the requirements of plywood in order to be labeled as specifically “marine grade” do seem to be a bit lacking. In fact, the standards aren’t all that different from those of exterior-grade plywood. (You can read the precise specifications on the APA website.)
In case you’re thinking that your application will require more weather-resistance than most non-marine-based exterior applications, you’re probably starting to realize the importance of having a more in-depth conversation with your lumber supplier. Like all plywood, marine-grade plywood comes with such a variety of quality levels, depending on the precise combination of elements, ranging from plies and veneers to preservatives and glue.
Customers can use the term “marine plywood” to mean a variety of things; sometimes, all they really need is exterior grade plywood – for the outside of buildings located near the coast, for example. Other times, it’s intended for structures that will be more directly exposed to punishment by waves, such as aspects of a marina; yet other times, it will be fully immersed in the water, as part of a boat.
By its nature, any plywood labeled as marine-grade will have a few characteristics in common. For one thing, its core will be free from voids, which could trap water and lead to rotting that starts on the interior. For the same reason, core plies will have very few repairs. The glue used to hold the plies together will necessarily be Weather and Boil Proof, or WBP glue. Having been subjected to boiling water without causing delamination of plies, WBP glue is understandably essential. But other than a solid core and weather-resistant glue, marine-grade plywood won’t necessarily meet any marine-specific standards.
Just because all marine-grade plywood doesn’t meet the standards which your application requires doesn’t mean you can’t ensure that the plywood that you order won’t; our point here is that you will need to specify what you need rather than assume it will be the case.
In Part 2, we’ll look at ways you can further specify the characteristics you desire for the plywood that you order, in addition to simply requesting “marine-grade plywood.”