A wooden raft likely evokes memories of the famous river-raft escape in the classic tale Adventures of Huckleberry Finn. While tying a few logs together might help you safely float down stream long enough to read a classic novel, you’ll need to be a little more selective with the wood you choose if you want your sailing vessel to stand the test of time. One step toward understanding why marine-grade plywood is important is to realize the distinctions between it and its two second cousins, pressure-treated plywood and exterior-grade plywood.
Also referred to as “wolmanized,” P.T. plywood is simply run-of-the-mill interior-grade plywood that has been subjected to pressurized chemicals in order to increase its rot-resistant qualities. The chemicals involved are arsenic and copper compounds that can actually be leached with repeated water exposure. Because P.T. plywood needs to be able to be penetrated by the chemicals, it is often made with soft woods, oftentimes with many gaps or voids.
Exterior-grade plywood has a void-free outer layer and is comprised of multiple layers that adhere to one another with the aid of water-resistant glue. However, gaps and voids may well exist in the interior layers of the wood, potentially allowing cuts to reveal gaps.
By contrast to pressure-treated and exterior-grade plywood, marine-grade plywood is free of gaps and voids in all the layers, which are laminated with a water-proof glue. Because of the care taken in the selection of wood and the adhesive used, water cannot penetrate the integrity of the wood. Marine-grade plywood seldom bubbles, warps, or comes apart, even when subjected to constant immersion. Even when you cut it, no voids will be revealed.
One of the bench marks of quality marine-grade plywood is that it is comprised of harder woods, such as Douglas Fir and Okoume. Known for its strength and ability to bend, Douglas Fir is the most economical option for marine-grade plywood. While its faces may have some patches or repairs, they will include no voids. The natural weather resistance of Douglas Fir makes it a durable option for use in boat-building or other sea-faring applications. One down side of using Douglas Fir plywood is that it is not known for having a consistent appearance.
When aesthetics are a factor, Okoume plywood is optimal. While Okoume wood lacks natural weather resistance, its tight, consistent grain and lightness make it a legitimate consideration. For plywood, it is treated with WBP phenolic glue and then laminated to its Fir core. With a finish like that of glass, Okoume marine-grade plywood is a popular choice for decking and other veneered applications, making it a favorite of boat-builders everywhere.
J. Gibson McIlvain’s inventory of marine-grade plywood includes a high-quality selection of veneer ply counts and thicknesses in both Douglas Fir and Okoume. For more information, visit McIlvain’s website or call them at 800-638-9100.
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