The Different Grades of Plywood

Plenty of woodworking projects have a bill of materials that include the use of plywood. Anything from construction of buildings to kitchen cabinets to aircraft all benefit from the use of plywood in the overall design. Plywood is made of large thin sheets, or plies, of veneer that are laid on top of each other with the direction of the wood grain rotated 90 degrees every layer. The layers are bonded together with adhesives and glues, resulting in a large, strong panel. Plywood offers a large surface area of coverage over using several planks of lumber. Many categories of plywood are even heat and water resistant, furthering their use in various environments. Now, choosing the right product can be tricky. You must determine what species, size, and thickness will do the job. But the most puzzling question you may ask when you visit the plywood section at your local hardware store is, just which one of these dozens of options is right for my project?

It all comes down to the grading system. Not all boards are created equal. That is, nature does not reproduce trees in the exact shape every time. Wood grades exist because of the varying quality of a section of wood in nature. Factors like soil quality, average rainfall, and even the local ecosystem can affect how a tree grows. The result is varying wood grain, knot size, knot frequency, etc. Ultimately, the appearance and performance of a section of wood changes from tree to tree. This may seem simple at first. There's good quality and bad quality, right? Not quite. Even the lowest grade could have the highest value for a specific project. Rather, this question is best answered by taking a look at what each grade offers and which will be most economically sound for the application.

The Plywood Grading System

Here are the six grades of plywood and how each can provide value to a woodworking project.

Plywood comes in either grade A, grade B, grade C, grade D, grade CDX, or grade BCX. As a general statement, board quality goes from A as the best to D as the worst. Furthermore, plywood will sometimes come with a double grade, such as A-B or B-B. In these cases, each grade represents one of the two sides of the panel. This is a regularly manufactured product because there are so many projects which only expose one side of a board, so rather than make an entire board out of higher quality veneer, it is more economical to make all but the one outside face a lower grade. In the cases of CDX and BCX, these use multiple veneer qualities as well as special adhesives. The X in these acronyms are often mistaken to mean exterior grade, however this truly means a special moisture resistant adhesive was used on the construction of the panel.

Grade A Plywood

The first and highest quality grade of plywood is Grade A. This is the pick of the litter when it comes to board quality. Grade A plywood is smooth and sanded, with fine grain structure throughout the entire board. There are no holes or voids across the entire sanded face, making this grade extremely paintable. Most of the time, boards are not grade A right off the mill. They are repaired during manufacture with approved methods so that the board is absolutely perfect before shipping. Painted indoor furniture or cabinets will best be made with this grade.

Grade B Plywood

The next grade is grade B, or B-Grade. This grade truly represents much of nature’s finest offerings for wood. Many boards tend to be close to B grade before any modification or repair is even done in the mill. This is because grade B begins to allow for more natural grain, larger unrepaired knots, and sporadic voids. Closed knots up to 1 inch in diameter are allowed. These boards are still very paintable if you can smooth out the few knots throughout the board. This grade also allows for very minor splits and discoloration of the board. Many applications use grade B plywood, including cabinets, outdoor furniture, and furniture. The natural and raw appearance of this grade of plywood gives each project plenty of strength in addition to character.

Grade C Plywood

The next grade is Grade C board. Grade C, much like grade B, allows for holes, voids, and knots. Closed knots up to 1 ½” in diameter are allowed, and knotholes up to 1” in diameter are allowed. Splitting is much less regulated on these boards. The edges and planes may not be as smooth as grade B, either. Appearance projects may suffer from the looser regulations of grade C plywood. Applications include structural framing and sheathing.

Grade D Plywood

The final major grade is grade D. Grade D wood is very rustic in appearance, featuring knots and knotholes up to 2 ½” in diameter, major splitting, and heavy discoloration. The grain structure will tend to be looser as well. While not the cleanest or most paintable, this grade of plywood is not without use. Grade D still requires the board to withstand stresses and loads so that it can be used safely in woodworking projects or large construction. Truly unwanted wood does not even fit in any grade, so you can be confident that even the lowest grade still must meet performance requirements. Many structural projects use this grade since the wood gets covered up anyway. The strength will provide a long-lasting structure at a great price.

Grade BCX Plywood

BCX plywood is also commonly found in the plywood section. This grade uses grade C plies and a single grade B ply on one face. The adhesives used are also moisture resistant. This specific product is commonly used for outdoor applications that still need to boast appearance, including being coated or painted. This type of plywood is used in projects such as siding on barns, farm vehicle paneling, and privacy fencing.

Now that you understand the different types of plywood, you can be confident in choosing the right product for the job. Whether it needs a great natural finish, a fresh coat of paint, or just needs to be strong, you will know what grade will work best for you.

Grade CDX Plywood

CDX plywood is a common example of a double graded board. As the name suggests, One side is made from grade C veneer, while the other side is made from grade D veneer. Oftentimes, the rest of the inner plies are made with grade D veneer to make it more affordable. A moisture resistant phenolic adhesive is also used to further increase the performance in wet or humid climates. This grade is optimal where large quantities of plywood are needed and most of it will be covered up anyway. CDX plywood is commonly used for exterior walls and sheathing. The grade C face provides a smoother surface for which contractors can use when installing the other parts of the structure, including weather resistant layers and siding. Roofing is another great use for CDX plywood.