Plywood Types
by Rick Christopherson

There are many different types of wood-based man-made materials on the market. Each has its own purpose, drawbacks, and benefits. When most people hear the term plywood, they think of CDX (or whatever...) which is used to build houses. Yet in the wholesale wood products industry, plywood is a generic term for any sheet product regardless of construction (for example; MDF, VC, CDX.) The two terms are interchangeable, more-or-less.

Medium Density Fiber Core Hardwood Plywood (MDF)
MDF is made from fine wood dust mixed with a binder and heat-pressed into panels. The sheets can be sold as-is, or a veneer skin, like oak or maple, can be laid up on the sheet. (The veneered sheet is the most common form, but blank MDF sheets are available as Paint-Grade)

This material is extremely stable to work with, and is typically very consistent from batch to batch. A 3/4" thick sheet purchased over a year ago is exactly the same thickness as a new sheet purchased today. The surface below the veneer is typically free of voids and blisters, resulting in a better veneer consistency and bond. With this better bonding of the wood veneer, there is less chipping during a crosscut operation. I have also observed that this material is easy to machine either by saw or router, and the cut edges are excellent for glue adhesion. (I have heard it mentioned that MDF is hard on cutters, but personally, I disagree with this statement. I feel that MDF is rather easy on the cutters.)

The primary drawback to this product is weight. A 3/4" x 4' x 8' sheet can weigh as much as 70 to 90 pounds per sheet. The density of the core is expressed as the weight of a one cubic foot (1'x1'x1') block of the material. Therefore, an MDF sheet using a 48# (pound) core, will weigh 96 pounds. (48"x96"x3/4"= 2 cubic feet)

Medium- and High-Density Overlay Plywood (MDO and HDO)
MDO and HDO consist of a core material, like laminated fir veneer, overlaid with a pressed fiber material. In short, this is a typical veneer core plywood (common plywood) with an MDF surface. This gives the best of both worlds; the weight is lower than a full MDF, but the surface is more stable than a veneer core plywood.

Veneer Core Hardwood Plywood (VC)
Veneer Core plywood is made from alternating layers of fir slices (common plywood) with a surface veneer of a finished woodgrain such as oak or maple. This construction gives VC plywood a distinct advantage over others in strength. This is a light weight material, and easy to handle.

The drawbacks of VC plywood are:

Lumber Core Plywood
Lumber Core Plywood is manufactured from strips of solid lumber, typically basswood. The core is then surfaced and a veneer layer is applied. This is one of the most expensive plywood types to make, and is commonly used for applications where the edges cannot be concealed or need to be routed.

As the popularity of this product diminishes, it is becoming more and more difficult to locate suppliers who are willing to carry high grade sheets. The quality of the core lumber is dropping in all but the best of grades. Most grades machine poorly. If the core is not glued up with consistent stock, voids can be present which will run the full length, or at least a portion of the full length, of the entire sheet.

Because of this, care must be taken in selecting sheets if they are to be used for matched and sequenced door material, as a flaw in the core can wipe out an entire set of doors if they need to maintain grain matching from one to another.

Particle Board Core Plywood (PBC)
PBC uses a coarser wood dust than MDF. Because of this, it has a slightly lower weight, but the edges and surfaces are not as smooth and consistent. Most melamine products use PBC as the substrate.

Melamine plywood is a thermally fused, resin saturated paper finish over a particle board core. It is highly stain and abrasion resistant. As a cabinet maker, I use a lot of this material. Even though glue manufactures claim to have developed an adhesive which bonds to the surface, I (personally) am not willing to take the chance; after all, this is a "paper" surface. (My personal recommendation to any one using this product is to dado the joints for better bonding.)

Contrary to popular belief among many woodworkers, melamine is not the name of the paper finish; it's the name of the resin used to impregnate the paper liner (chemically C3H6N6). Even among manufacturers of this type of sheet product, however, it is still called melamine.

This material comes in a variety of colors, is highly stain and mar resistant, and is commonly used in the cabinet industry for carcass construction.

Depending on the grade of melamine, it can be brittle or soft, coarse or smooth. Typically, the higher grades of melamine are more brittle and will chip during machining but have a thicker surface and greater resistance to abrasion.

I have found that the best blade for cutting melamine is a triple-chip laminate blade set with a blade height of about 1" above the top of the wood. With a higher blade height, there will be excessive chipping on the back of the sheet, and with a lower blade height, there will be some chipping on the top of the sheet. The reason for the top-side chipping with a low blade height is due to the teeth striking the surface veneer nearly perpendicular, and throwing chips forward.

High Density Maple/Birch (Baltic Birch or Appleply)
High density plywoods (HDP) typically come in either maple or birch specie. Unlike common plywood, HDP has many more plies, is generally void free, and uses a stronger species than fir. HDP is commonly used for drawer side material as it is strong, stable, and has a moderately attractive edge

Baltic Birch
Baltic birch is probably the most common type of HDP, and uses birch as the substrate. This will come in 5' x 5' sheets. For a 1/2" sheet, there are typically 7 to 9 plies. Being birch, the surface does not finish as nicely as the maple counterpart, and there is a tendency for splintering at the edge of a machined cut.

Appleply is a manufacturer's name for high density maple plywood. From a fabrication stand point, it is similar to Baltic Birch, in that it carries about the same number of plies, except Appleply comes in standard 4'x8' sheets. Because the surface is maple, there will be slightly more grain pattern on the surface, and the surface will sand much smoother. There is less splintering of the machined edges, and those splinters which do appear will be shorter and less inclined to align with the edge.

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Copyright 1998, Rick Christopherson