Of all the types of plywood available on the market, CDX grade plywood is the most commonly available in lumberyards and building centers. This softwood plywood is the least expensive grade of multi-layered veneer plywood, manufactured in small factories around the country for local use, predominantly in construction.
CDX plywood is manufactured, like other types of softwood plywood, of opposing layers of wood veneers, laid at right angles to each other and glued together with resinous glue. There are always an odd number of layers, balancing the sheet, to prevent warping of the panels. Actually, the odd number of veneer layers allow for an even number of glue layers. An odd number of glue layers would cause the glue to pull towards one direction, causing warping of the panel.
Softwood Plywood Grading System:
The letters “CDX” refer to the grade of plywood panel. Most plywood is graded based upon the finish of the exterior layers, specifically the amount and type of defects that are allowed in these layers.
|A||Face veneer is practically free from all defects. Smooth, paintable surface. Limited number of patches.|
|B||Solid, more knots than A grade, possible minor splits.|
|C||Limited splits, discoloration or sanding defects that don’t affect the plywood’s strength.|
|C plugged||As its name implies, the splits and defects have been plugged.|
|D||Unplugged knots and knotholes up to 3 inches, splits and other defects allowed.|
Although available, it is rare to find plywood where both sides are the same grade. This is essentially limited to hardwood plywood that is used for cabinetmaking. Most plywood is graded with two letters, showing the face and reverse side grading of the plywood.
Based upon this grading system, we can see that CDX plywood has one side that is “C” grade and one that is “D” grade. The “C” graded side is the face side, used where it is more visible, and the “D” graded side is the reverse side, usually mounted in a way that hides it.
Interior Verses Exterior Plywood
The difference between interior and exterior plywood is in the resin glue which is used to hold the various layers of veneer together. Exterior grade plywood, marked with an “X” after the surface grade uses a resin that is more water resistant than interior grade plywood. It can also mean “Exposure grade 1” which stands for damp-proof plywood used for demanding environments such as underlayments and roof sheeting. “CDX” plywood is an exterior grade plywood only when considering the adhesive used for connecting the plys, since the wood isn’t waterproof.
CDX Plywood Thickness Availability
As the most common plywood product available on the market, CDX plywood is available in a number of thicknesses, ranging from 1/4 to 1-1/4 inch thick and also including 3/8, 1/2, 5/8 and 3/4 inch thicknesses. Please note that these are nominal thicknesses. The actual thickness of these plywood sheets will be 1/32 inch less than the nominal size, due to finish sanding of the sheet.
Common Uses for CDX Plywood
CDX plywood is used for a number of applications, including:
Construction sheathing of walls and roofs
Constructing crates and boxes