The average lumberyard or home improvement center today carries a plethora of different types of plywood, giving you a wide selection to choose from. Businesses which specialize in providing architectural trim for cabinetmakers and contractors will have even more choices, especially if you’re looking for hardwood plywood. Of course, not all plywood is created equal, so you need to know what you’re looking for and have an idea of what the different types of plywood are.
There are many types of plywood, including a wide range of engineered wood products which are referred to as “plywood” even though they aren’t made like traditional plywood. Of those which are made according to the traditional formula of thin veneers, laid crosswise to each other and bonded together, we can break plywood down into two basic groups: hardwood plywood and softwood plywood.
Generally speaking, softwood plywood is only used for construction, although many do-it-yourslefers also use softwood plywood for painted wood projects, even furniture. Nevertheless, most softwood plywood doesn’t have a good enough appearance to be used for furniture projects, because it is not finished for that; rather, it is provided with a finish that is intended to remain hidden in use.
Of these softwood plywoods, the most common variants you’ll find in your local home improvement center are BCX, CCX and CDX. To understand which one you need for your project, we need to understand their similarities, as well as their differences.
Understanding Plywood Nomenclature
Plywood is graded based upon the surface finish. This grading scale is different for softwood plywood, than it is for hardwood plywood. Hardwood uses a number system, while softwood uses a letter system. Additional ratings may be added, covering how the plywood is manufactured and any specifications it has been manufactured to meet.
With softwood plywood, a three letter code is used to define the grade. The first letter of the code talks about the face, or front side of the plywood, the second letter of the code discusses the plywood’s back side, and the third letter tells you whether the plywood is suitable for interior or exterior use.
- Grade “A” refers to the surface being sanded smooth and paintable. Some manufacturing repairs are acceptable, but they must leave the surface smooth and without defects
- Grade “B” provides a solid surface, with some repairs allowed. These are usually football shaped pieces which have been pieced into the surface veneer. May have tight knots, without any missing wood, up to 1 inch in diameter. Some small splits and discoloration are allowed.
- Grade “C” allows for tight knots up to 1 1/2” and open knotholes up to 1”, along with some splits and discoloration.
- Grade “D” is the lowest grade, with knots and knotholes up to 2 1/2″, along with some splits. No repairs will have been done to improve the quality of the surface veneer.
It should be clear that A and B grade plywood will provide a much better finish veneer than C and D grade. This comes at a cost though, as these higher grades of plywood are more expensive.
In the case of plywoods ending in an “X,” such as ACX, BCX and CCX plywood, the “X” stands for exterior grade adhesive. This means that an adhesive has been used in the construction of the plywood, which is able to withstand moisture. The plywood itself has been treated to some extent, to withstand getting wet, such as during construction. However, it is not pressure treated wood or any other that is intended to last outdoors. The treatment the plywood receives is only enough to protect it during construction.
Softwood plywood may also be Marine grade or be rated as Water Boil Proof (WBP). This is a specification for a sample of the plywood, made in the same way with the same materials, having been immersed in boiling water for an extended period of time, without delaminating.
Marine grade ACX plywood is softwood plywood with an A grade face and C grade back, just like any other ACX plywood. The difference comes in the core of the plywood. With any marine grade plywood, the veneers in the core must be without any voids. This is necessary in marine applications, because voids allow moisture to collect, allowing delamination of the plywood to begin.
A and B grade plywoods are typically suitable for finish material, while C and D grade plywoods are considered to be best for construction projects. It is unusual to find plywood which is graded the same on both sides, although it is not impossible. Nevertheless, in general, plywood sheets will have a face side and a reverse or back side, with the face side being of higher grade than the back.
BCX plywood has a handsome, well-sanded face and a less-finished back side. It typically contains C-grade inner layers and is bonded with exterior glue. BCX comes in a variety of thicknesses. The thickness of this plywood is normally measured in 32nds of an inch; with the standard sizes being 1/32” smaller than the nominal thickness. So, 3/8” plywood is actually 11/32” ½” plywood is actually 15/32”, 5/8” plywood is actually 19/32” and ¾” plywood is actually 23/32”.
These utility panels are best for work buildings, farm construction projects, truck and boxcar linings, and similar projects. You can make painted projects out of them, especially in cases where only one side needs to be showing. They make an excellent base for the application of exterior coatings. You may find that these panels have been pressure treated; but if so, they will be specifically stated as such.
Is there an ACX Plywood?
ACX plywood is a variation on BCX. In many mills, BCX plywood is plywood that has been manufactured and then determined not to be good enough to be rated ACX. While both can be used in the same manner, the better face veneer of ACX plywood makes it ideal for visible exterior panels on a home. It uses the same rosin and surface treatment against moisture as BCX plywood, allowing you some time before painting the wood. However, the longer you wait to paint it, the more damage it will incur.
What is ULX Plywood?
ULX is a brand-specific name for BCX plywood sold by Lowe’s and possibly some other outlets. While an exterior grade plywood, it is not marine grade or pressure treated. Therefore, it is not impervious to moisture, decay and termites. ULX plywood should always be treated with a wood preservative or painted, when used in an outdoor application, unless it is to be covered by a waterproof layer, such as siding or roof shingles.
Generally speaking, this rating is used mostly for MDF and other engineered wood panels, which are not made according to the same method as traditional plywood panels, even though they are considered a plywood product.
CCX plywood is unusual and difficult to find. Nevertheless, it is a standard grade of plywood, often made with pressure treated softwood. This type of plywood has more blemishes than BCX plywood, and both the face and the back have the same characteristics. Just like BCX, CCX plywood comes in a wide variety of thicknesses, normally contains C-grade inner plies, and is bonded with exterior glue.
CCX Plywood is great for construction projects of all types, but keep in mind that the veneer will typically display lots of knots and other visual blemishes that detract from its appearance, and the sanding process it has been through is less intensive than that which higher-grade plywood undergoes.
Often, when people are looking for CCX plywood, they are directed by the lumberyard to CDX plywood, which is the standard grade of plywood used for sheathing on homes. The difference in CCX and CDX is only on the back side, which is not normally visible in construction.
In many construction projects, ACX or CDX plywood might be used for sheathing or underlayment. While this works fine, voids in the core layers of plywood can cause sponginess or premature delaminating of the wood, especially in cases where high floor loads are expected or where some flexibility in the floor is required.
The solution is to use a plywood product without voids. One option for this is to use marine grade plywood. Another option is PTS plywood, which stands for plugged, touched and sanded. This refers to the manner in which the plywood has been manufactured. During that process, all knotholes are cut out, plugged and then finished to match the surface and thickness of the rest of the veneer layer. This extra effort provides a superior plywood product for underlayment, where you don’t have to worry about voids or unevenness in the sheets.
If you are needing plywood that has greater resistance to moisture than normal exterior grade plywood, you might want to consider GC plywood. This rating refers to plywood that is intended for actual “ground contact”, hence the name. GC plywood is always pressure treated, protecting it from rot and decay, making it truly impervious to the normal decay that happens in wood that is in contact with the ground.
The protection applied to GC plywood also protects it from termites, making this plywood ideal for backyard storage sheds, decks and any other backyard construction, which may have direct contact with the ground. While other wood left in contact with the ground will be attacked by termites, GC plywood will not.
Typically, GC plywood will be tinted, due to the rosin that is used to pressure treat it. Different companies may tint it green or yellow, mostly as a part of their branding. Which one is best is mostly a matter of personal opinion.
Professional Recommendations for Use
BCX plywood is readily available, but CCX not quite so much so. Both are suitable for exterior use. Be sure to consider appearance when making a decision about which of these plywoods to use, selecting BCX when looks are more important. Both types of plywood can be painted. Remember that hardwood cannot be pressure treated, and look for pressure-treated softwood if extra durability is important to you. Finally, ensure that you choose the right thickness for your project to ensure that it will be able to stand up to the elements while performing the way you need it to.