Plywood/OSB

1. Most thicknesses available in 5×5 and 4×8 sheets, see Baltic Birch Plywood section above.
2. Availability is very limited.
3. Comes in Fir and Meranti versions, see the Plywood Terms/Definitions section below.

9’ and 10’ sizes

ONLY applies to OSB. Generally made only for WALL sheathing for 9’ or 10’ walls, eliminating using 8’ sheets and then piecing in the rest. Must be used vertically. Not generally used for other purposes. 4×10 is available in some AC thicknesses.

APA

The APA, American Plywood Association is the trade industry group determining rules/standards and definitions of plywood made/sold in the United States.

Baltic Birch

The real Baltic Birch plywood product comes from Norway, Finland and Russia. Multiple plys, few voids, great for cabinets and other fine woodworking. Paints well, alternately accepts stains/sealers more uniformly in color. Comes in both 4×8 and 5×5 sheets, although the pricing on a per square foot basis will be less for 5×5 sizes.

BBOES

BB grade face plys, oiled and edges sealed, hence BBOES. Used for concrete forming. strong, and with the oil sealing, releases off concrete better when dried.

Bending Plywood

Unlike most other plywood, where the plies are alternated in direction to increase rigidity and strength, having the plys all in one direction allows the sheet to be bent. Very limited size availability; generally only in ⅜” thickness. Sheet size is called 8×4.

Book-Matched

When veneers are cut, veneers that are mirror images of each other are used to create a visual effect by gluing adjacent to each other like pages of an open book. Think of cutting an apple in half; each half mirrors the other.

Cross Plys

Inner plys are laid at 90-degree angles from each other to add to strength and stability.

Douglas Fir (DF) vs. Southern Yellow Pine (SYP)

Most plywood sold in our area of the country is made from DF. Some notable exceptions: hardwoods, treated, specialty panels. SYP is dominant in eastern and southern states. SYP may be less expensive however with Colorado’s dryness and UV, SYP tends not to perform well.

Face Grade

Each face has a grade; therefore a “CD” grade has one C face and one D face. (Note: hardwood plywood is NOT graded this way.)
A: Sanded, good-looking veneer, however, may NOT be a true/full “appearance” grade. Minimal knots, can have up to 18 football patches per face, putty fill-in, etc. Some thicknesses available in 4×10 sheets also.
B: Sanded veneer allowing for defects such as solid in-place small knots.
C: NOT sanded, irregular surface.
D: NOT sanded, irregular surface.

Formply

Any plywood made for forming concrete; strong, few voids, see BBOES.

Full Face (FF)

Applies to T&G panels. The sheet size is slightly larger as the face is 4×8, NOT including the width of the tongue, therefore sheet width is approximately 48½”. This distinction is important because if overall size is 4×8, with floor joists laid 12”, 16” or 24” on center, very soon the panel joints don’t line up with the joists.

G1S/G2S

Good one or two sides.

Heat Treated

As a rule, ALL plywood has been heat treated as heat and pressure has been used in its manufacture.

Machines Well

Means that cutting, routering, drilling, etc., is done with ease and leaves clean holes, edges, and cuts.

Marine Grade

All are an AB grade:
• True marine plywood is made with more plys than other “marine” plywood in both meranti or oleume veneers. Locally, we get what we get! Generally produced in true net thicknesses.
• Lower standards of marine, usually in Douglas fir veneers, under a standard called PS1-09.
• Both faces must be of similarly graded veneers.
• The adhesives used must highly resistant to moisture, weather, steam, dry heat and micro-organisms.
• Must have very low moisture content.
• Both have minimal voids and better glues than exterior plywood.

MDF Core

Most common plywood is constructed with multiple plys/veneers, however, in hardwood plywood, MDF core is used commonly as it lowers the sheet cost, eliminates any voids, very flat/stable panel, but is heavy. Cutting MDF creates sawdust some users don’t like, however it does machine very well.

Medium (Heavy) Density Overlay (MDO/HDO)

Plywood covered (overlaid) on one or two sides with a kraft paper (think similar to a butcher paper) with a chemical coating to provide a superb painting surface. By definition, this plywood has limited voids and has an A or B veneer just under the paper overlay.

Mill Option

On the “bad”/non-graded face) face, the mill can choose what grade/type of veneer is used. Therefore, it may not match the good face. Generally, this is to save money. Also, these odd grades/types of veneers apply generally only on thinner sizes as most ½” and ¾” are constructed in good two side or with veneers that are at least the same wood type as the good/graded face. Mills have wide latitude on using a variety of veneers which can be used on the inner plys/layers. Inner plys are not generally full size (i.e., 4×8), especially those laid crosswise. They have been pieced together.

PATCHES, AKA “FOOTBALLS”.

These are patches used when a defect (like a knot) is cut out of an otherwise good veneer. This leaves a solid face; however, those footballs may seal differently than the surrounding veneer.

PB vs. IPB vs. MDF vs. HDF.

At least some availability in odd sizes: 5×8, 4×10, etc. Looking at the edge of a piece of particle board will reveal how compressed the sawdust is. As progressively better versions, the compression is more and more evident. In order of weakest to most compressed:
PB: “Plain” particle board; used in floor underlayment.
IPB: Industrial grade particle board; generally used for shelving. Dense towards the faces, middle of thickness is fairly flaky.
MDF: Medium density fiberboard; very dense with some less density towards the center.
MDX or MEDEX: Exterior grade MDF.
HDF: Heavy density fiberboard; very dense throughout thickness.

Plain Slice vs. Rotary Cut

Plain slice veneer is cut like a loaf of bread, the log is simply sliced thinly. Rotary cut means the log has been peeled like an apple. There is more repetition in rotary cut (and cheaper) as the veneer is just one long ribbon, however, the veneer pattern repeats every time the log rotates around in the peeling process.

Plys (Plies)

The number of veneer layers in a sheet of plywood. As a rule, the more plys, the better the grade of plywood; more plys add stability and strength. Generally, there are an odd number of plys used. Veneers can be made with most types of wood, however, the most common are southern yellow pine and Douglas fir. In hardwoods, the most available are birch, walnut, oak, cherry, maple and mahogany. For example, in ¾” thicknesses:
• Baltic birch has 13 plys
• AB/AC plywood are probably 7 plys
• CD plywood will mostly have 5 plys

Putty

Used especially on grade A and B veneers to fill in missing/cracked veneer. This IS acceptable under grading rules.

Sanded

Any plywood that has been sanded; this sanding may not be to a final grit or “ready to finish”. Generally, only A and B faces are sanded as are ALL hardwood plywood. Note: sanding too much will literally sand thru a veener!

Sign Grade

Any plywood made to provide a smooth, easily paintable surface. MDO is the best example.

Tempered

Heat treatment on hardboard panels to make more oil and stain resistant, as well as harder. Generally, all pegboard is tempered.

Thickness

Most plywood, as many other wood products, are “scant”. In the case of plywood, generally the actual thickness is 1/32” LESS than the named thickness. For example, ¾” actually measures 23/32”. Marine and particle boards generally are true full measure net sizes.

Treated Plywood

Similar to treatments used on lumber. As in lumber, SYP takes on a treatment very well compared to Douglas fir. Treated plywood is “standard” CD or AC plywood that has then been treated and kiln dried after treatment (for stability). Noncom treatment is more of a salt-based variety. Merchandise should be stored inside as the salts can wash away with rain/snow. ACQ-treated plywood is generally treated to a 0.60 penetration for maximum rot resistance. Still is NOT meant for below grade applications. Dyes are added (red/fire; green/rot treated) for easy identification. Otherwise treatment solutions are more transparent in color.

UL

Underlayment grade. Generally, very small voids in inner plys. B faces on exposed face. Generally, has T&G edges to interlock to minimize movement on sub-floors, etc.

Voids

Holes in the veneer where knots fell out during peeling the log (and presumably NOT filled).

X / Exterior Glue

Panels was made using exterior glue but is NOT meant for constant weather exposure. For example, CD plywood and OSB are made with exterior glue, but are meant to be covered by roofing, siding, etc., within a certain time period, allowing for construction.