Plywood has become a widely used outdoor building material because of its adequate strength and affordability. But, believe it or not, not all exterior plywood grades are created equal when it comes to withstanding external elements and conditions.
If you don’t want to make the mistake of choosing the wrong type, let me give you a quick guide on how to differentiate them.
What Is Exterior Plywood?
Newbies may not know, but plywood is processed by peeling wood logs into thin veneers. These durable composite materials are joined together by binding, pressing, and heating.
If you look closer, each layered grain only goes in one direction, and that’s because the veneers are set at different angles.
The alternating layers in plywood help minimize contraction and expansion. Personally, I find it more stable than the typical 2×4 wood.
The unique composition of plywood helps it resist warping, shrinking, or breaking when used in construction. I always recommend using at least three plies for enhanced durability. The more plies you have, the sturdier it becomes.
Different Grading of Exterior Plywood
If you scan the wood market, you’ll quickly realize these plywood materials are graded based on size, thickness, and appearance. Depending on the variation, they are labeled with two to three letters that dictate the plywood grading specifications.
The first letter signifies the front veneer grade, while the second letter refers to the veneer’s back. Plywood materials great for exterior use have the third letter, X. That said, join me as I delve into some of the best options for outdoor construction.
ACX
As the letter “A” is included in its label, you can expect ACX plywood to be smoothly sanded in its front veneer. It has a good wood grain, making it suitable for painting over.
Meanwhile, its back is categorized in grade C. This plywood’s tightened knots are around 1 ½ inch with 1-inch knotholes. Although it may have patched areas, you can use it for subflooring projects.
ACX plywood is readily available in various sizes. Depending on its thickness, you can purchase it in options ranging from ¼-inch to ¾-inch. I’ve also come across some manufacturers that offer ⅜-inch thickness through special orders.
ABX
Like ACX, the ABX variations are smooth and paintable materials as they’re graded A plywood types. Because they have visually pleasing attributes, many construction professionals[1] and woodworkers use them for furniture-making projects. Its back veneer belongs to grade B, so expect some patches and filler.
Most ABX plywood in the market comes in 4 inches x 8 inches in overall size. As for the thickness, your choices are narrowed down to ½-inch and ¾-inch thick.
CDX
When wood shopping, you’d likely find CDX plywood readily available; it’s such a common material. The face side of this wood is graded as a ‘C’, which means it has knots up to 1.5 inches in diameter.
The plywood will show minimal splits and discoloration, but in my experience, these imperfections don’t compromise the material’s strength. However, it’s typically best used in non-visual applications where aesthetics aren’t a primary concern.
And because its back veneer is also graded D, its flaws are slightly more noticeable than other plywood types. Its knotholes can range up to 2 ½ inches, and its surface is rough and unsanded.
As for its market availability, you can only purchase it in 4 x 8 inches variations. The thickness options you can choose are ½-inch, ⅝-inch, and ¾-inch.
Materials Used for Exterior Plywood
As exterior plywood materials are exposed to harsh and changing weather conditions, it will help if you could apply a sealant over its surface. Proper sealing can prevent water and moisture from damaging the wood.
You can opt to use a polyurethane varnish, and I recommend apply at least two coats for extra protection. On top of that, you can protect the surface of the plywood with waterproof paint.
Materials like phenol-formaldehyde glue are also encouraged as they can resist exposure to water and weather.
Conclusion
Now that you’re well-versed in exterior plywood grades, you can lay down the worries of choosing the wrong wood variation.
Beyond just checking the labels, I’d recommend keeping in mind the appearances and attributes I discussed earlier. Through this, you’ll be better prepared and less likely to be misled the next time you’re out shopping for wood on your own.
You've probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.
Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.
- Makita XCU03PT1 Review (2023) — A Cordless Chainsaw Powerhouse - November 29, 2023
- Greenworks 24V 13-Inch Brushless Push Lawn Mower Review (2023) - November 29, 2023
- Ryobi P1108BTL One+ Review (2023) - November 27, 2023
