Technical Info

WFRG staff is available to provide technical information and assistance on all aspects of wood flooring selection, installation, and maintenance. For larger projects, we will seek to engage directly with project contractors and sub-contractors to ensure that job-site conditions are correct and that our wood flooring is handled and installed properly. The great majority of potential problems with wood flooring can be avoided if site conditions are correct and our installation guidelines are followed.

This section of our website also contains extensive technical information on all aspects of wood flooring including: 

• Solid vs. Engineered Wood Flooring 
  • Solid Wood Flooring
  • Engineered Wood Flooring
    • 2-layer Engineered
    • 3-layer Engineered
    • Multi-layer Engineered
• Flooring Construction - Wear Layer Configuration
  • Single-strip
  • Two-strip
  • Three-strip
  • Sawn vs. Veneer Wear Layers

Solid wood flooring is milled from lumber and each plank is a single species and piece of wood throughout its thickness and width. It is commonly available unfinished and the standard thickness is 3/4”, although today solid flooring is also available factory-prefinished. Solid wood flooring that is 2-1/4” wide (or less) is called strip flooring, while solid wood flooring that is 3” wide or more is called plank flooring. Because it is made from solid wood, widths wider than 6” or 7” are rare, not because solid wood doesn’t come that wide but rather because solid wood isn’t as stable in service as engineered wood and shrinks/expands too much with changes in relative humidity. Most solid flooring is mixed grain.

 2-layer engineered flooring is typically comprised of a thicker sawn wood or veneered wood face which is bonded to a plywood substrate, hence it is called 2-layer even though the plywood base is comprised of many plies of veneer.  It is typically produced with a 2 to 4 mm (approx. 1/12” to 3/16”) thick wear layer and is usually 10 to 15mm thick (3/8” to 5/8”) thick overall. The wood underneath the wear layer (i.e. the visible part of the flooring) is typically a 5- to 9-ply plywood base.

3-layer engineered flooring is typically comprised of a wear layer of sawn wood or rotary-peeled veneer 2.5 to 5mm thick (1/8” to ¼”) which is bonded to sawn-wood (usually softwood) cross-slats typically 8 to 10mm thick (3/8” to ½”) thick which is then bonded to a thin veneer (usually softwood) back that is typically 2mm thick. The central layer of wood underneath the wear layer (the visible face of the flooring) is called the core and the bottom layer is called the back.  Overall thickness is typically ½” to 5/8”.   This construction is also known as the “Scandinavian Floating Floor” style as it originated in Sweden which introduced both this style of flooring and the floating installation method to the world.

Multi-layer engineered flooring has either a sliced or rotary-peeled veneer wear layer that typically varies from .6 to 2 mm (1/32” to 1/12”) thick and is bonded in a multi-ply fashion to other layers (typically 3 to 7 plies) of rotary-peeled veneers, including a back veneer which many times is of a similar species in density if not the exact same species as the face veneer (for balanced construction). The overall thickness typically ranges between 7 to 12 mm (5/16” to about ½”). This flooring is essentially plywood.

HDF-core engineered flooring typically has a .4 to .6mm (1/64” to 1/32”) sliced veneer wear layer which is bonded to an HDF (High-Density Fiberboard) core and to which a thin back layer of veneer or paperface is added to make a balanced panel.  Flooring made this way is typically 6 to 10mm (1/4” – 3/8”) in thickness overall. This type of flooring is similar in construction to plastic laminate floors but uses a wood veneer as a face instead of a paper/plastic film image of wood/stone etc on the face like laminate floors do.

Single-strip

Pictures needed

In single-strip engineered flooring, a single (usually sawn) wear layer face is laminated to the core or backer layers underneath. Each piece is milled T&G and the lengths may be fixed or random.

Two-strip

Pictures needed

Two-strip engineered flooring has two strips or rows (lamellas) of wear layer wood that are laminated side-by-side to the core or backer layers underneath. So on the face each individual “plank” of flooring has 2 side by side distinct pieces of wood on top. And in each of the two rows they can have either one or multiple pieces making up the length. When installed, the lamellas are most clearly visible, but you can also see the individual double rowed “planks.” The appearance that results is “busier” look than single-strip or most solid flooring with non staggered ends that reveal the panels.

Three-strip

Pictures needed

Three-strip engineered flooring has three rows (lamellas) of wear layer wood side by side that are laminated to the core or backer layers underneath. The resulting individual “plank” of flooring has many distinct pieces of wood on top three wide as typically each row is comprised of many short pieces in length. When installed, the lamellas are most clearly visible along with the three rows ending at the same place in the floor at the end of the panel. The appearance that results is a much “busier” look. However, because the relatively small pieces of wood on top can be produced efficiently, there is typically a cost savings over single and 2 strip.

Sawn vs. Veneer Wear Layers

As the name implies, sawn wear layers are cut (sawn) from solid lumber and as such look like solid wood. Sawn material typically is more visually varied than veneer is.  Most sawn wear layers will have mixed grain orientation. Some wear layers are veneer, which can be either sliced or peeled.

Wood 101

• Hardwoods vs. Softwoods
• Wood Structure and Composition
• Heartwood vs. Sapwood
• Wood Grain
• Wood Figure
• Why Wood Moves
• Differential Shrinkage
• Wood Stability
• Moisture and Wood
• Wood Hardness
• Color Change in Wood
• Lumber
  • Grain Orientation: Mixed Grain, Quarter-sawn and Plain-sawn
  • Performance: Quarter-sawn vs. Plain-sawn
• Veneer
  • Sliced Veneer
  • Rotary Veneer

Hardwoods vs. Softwoods

Hardwoods come from broad-leaf (deciduous) trees. Softwoods come from needle-bearing (coniferous) trees. Most hardwoods are harder than most softwoods, but there are notable exceptions. For example, Balsa is a very soft hardwood and Australian cypress and Heart pine are hard softwoods.

Wood Structure & Composition

The structure of wood resembles a bundle of "straws": long, tiny conduits that transport nutrients and water up and down the length of the living tree. When wood is milled, these "conduits" look different when viewed lengthwise on the side or face of a board -- making up what is usually referred to as the "grain" of the wood -- than they do when viewed from their severed ends, as on the ends of a piece of lumber.

Wood is composed of fibers of cellulose (40%-50%) and hemicellulose (15%-25%) held together by lignin (15% to 30%). At the molecular level, the main components of the preceding organic compounds are carbon (about 50%) and oxygen (about 40%).

Heartwood vs. Sapwood

Trees grow in thickness from their center by adding cellular "conduits" at the outside of the tree. Some of these cellular conduits (the phloem) conduct the products of photosynthesis, mostly sugars, out from the leaves and downward and outward to the rest of the plant; some(the xylem) conduct water with dissolved minerals up from the roots to the leaves. The xylem are inside of the phloem. As the tree grows and ages, the xylem closer to the inside of the tree cease conducting fluids and die. The very dead xylem becomes the "heartwood," and the newer xylem outside it, still serving as plumbing, forms the "sapwood." In many woods, the sapwood and heartwood are clearly differentiated, the sapwood often being much lighter.

Wood Grain

The term "grain" is an imprecise one that usually refers to the narrow stripes that run along the length of the wood as a result of one of the following physical characteristics of wood: 1) the cell structure, as referenced above; 2) the appearance of growth rings, concentric rings that radiate out from the center of the tree, each ring representing one year's growth; 3) other physical features such as medullary rays, blades of tissue that run from the center of the tree to the outside that provide some linkage between the elements of the xylem and phloem and also act as a food store for the whole truck.

Wood Figure

The term "figure" most commonly refers to regular or irregular bending in the wood grain that causes the surface of the wood to capture and reflect light in interesting ways. A highly figured wood does so most dramatically, while a plain or straight grained wood may have little or no figure. Some species are more prone to having figure than others, and some species are known for producing a particular kind of figure: hence "birds-eye maple," "fiddleback mahogany," and "sapele pomele" all refer to to particular kings of figuring that are common (but not exclusive) to these species. Generally, figuring is a prized feature of wood and highly figured wood finds its way into high-end applications like architectural veneer, musical instruments, custom furniture, etc.

Why Wood Moves

Wood is hygroscopic, which means that it absorbs and loses moisture with changes in the relative humidity of the air that surrounds it. The moisture content of wood will always gradually equalize with ambient humidity. All wood expands or shrinks when it gains or loses moisture, changing size in width and thickness but only nominally in length.

Differential Shrinkage

Wood moves primarily along two different "dimensions": radially (i.e. perpendicular to the grain or growth rings) and tangentially (i.e. tangentially to the grain/growth rings). Different species move at different rates, but in general the ratio of tangential to radial shrinkage is 2:1. For North American species, tangential shrinkage ranges between 6 and 12%, meaning that a 6" wide board, when dried, can shrink as much as 3/4".

Wood Stability

Wood species and products that move relatively little when they gain/lose moisture are considered more stable than those that move more. Stability is important for products like wood flooring, because less stable woods are more prone to problems like cupping or gapping. In general, tropical woods are more stable than domestic woods, and quarter-sawn wood is more stable than plain-sawn wood. Because of their cross-ply construction, most engineered wood flooring is far more stable than solid wood flooring.

Moisture and Wood

Because wood is hygroscopic, moisture causes it to move. This means that wood flooring and moisture DO NOT mix well. In fact, most failures of wood flooring are due to moisture-related problems, including wet-mopping, flooding, inadequately cured concrete slabs, and HVAC systems that create job-site conditions that are either too dry or too moist before the wood flooring is installed. Radiant heat subfloors and regions that have significant fluctuations in humidity also pose challenges to wood floors.

Wood Hardness

The standard measure of wood hardness is the Janka test. It measures the force (in Pounds per Square Inch, or PSI) required to drive a steel ball .444 inches in diameter into a given wood to the depth of half of the ball's diameter. Red oak, the wood flooring industry standard, is 1290 on the Janka scale. Maple, often used for sports floors, is 1450. A number of exotic species are 3000+ on the Janka scale. In general, most tropical woods are harder than most domestic woods. For high-traffic applications, it is obviously a good idea to use harder woods.

Color Change in Wood

Some wood species change color dramatically as they age (oxydize). Others change color when exposed to light (UV radiation). Some do both. People who use wood flooring should expect the wood to change color over time unless it is heavily stained.

Lumber

Lumber is rectangular boards milled from logs, and the way the log is milled will determine the grain orientation of the face (the wide part) of the material. This in turn affects the appearance and the performance of the wood.

Grain Orientation: Mixed Grain, Quarter-sawn and Plain-sawn

Mixed grain includes a mixture of plain or flat-sawn and  rift- or quarter-sawn material. Material that is plain sawn is cut from the log such that the flat face of the board is tangential (or nearly so) to the growth rings. Depending on the exact angle of the cut and the part of the log the board comes from, the appearance of the face of the board will vary widely, often yielding a “flower figure.” Rift/quarter-sawn material is cut from the log in such a way that the flat face of the board is perpendicular (or nearly so) to the growth rings. This yields a uniform, linear graining without the wide varied appearance found in plain-sawn material.

Pictures here

Producing rift/quarter-sawn material is less efficient than plain sawing, so most lumber (and solid flooring or engineered flooring wear layers) is offered out  plain-sawn with only the small percentage of straight-grained material that develops mixed in.

Plain-Sawn Technique

(Top Half)

Quarter sawing produces both Rift (bottom right, either side of center) and Quartered (bottom left)

(Bottom Half)

The growth rings in plain-sawn lumber are at less than a 30° angle from the face of the board.
In rift-sawn lumber, they are at a 30° to 60° angle to face of the board.
In quarter-sawn material, growth rings are at a 60° to 90° angle to the face of the board.

All tree species have a physical characteristic called medullary rays which radiate out from the core or pith of the tree. Some species like oak have large rays while in others, the rays are small and do not significantly affect the appearance of the wood. When oak is quarter-sawn, the saw actually splits the large medullary rays lengthwise, causing it to appear shiny or reflective in what is typically called a ray/fleck figure (a pronounced physical feature that is often found in Arts & Craft-style furniture).  The angle of rift-sawn material is such that the medullary rays are cut at an angle instead of lengthwise, and the resulting grain has little ray/fleck and instead has a linear, comb-grain appearance.  Typically only the oaks are offered in either a mixed straight-grain selection of quarter/rift-sawn or also in a quarter-sawn selection showing lots of ray/fleck or in a rift-sawn selection showing straight grain and little ray/fleck.

Performance: Quarter-sawn vs. Plain-sawn

Appearance is not the only reason why quarter- or rift-sawn material is sought after. It also:

• Shrinks or swells less in width (ideal for flooring in extreme conditions)
• Reduces twisting, warping and cupping.
• Wears better as it is harder than flat sawn
• Has less propensity to surface check or split.
• Produces a better paint surface.

Quarter sawing is more of an art than plain sawing. It takes larger logs to quarter saw lumber, more production time in sawing each "quarter,” and wastes more of the log - all of which equates to a premium price for a premium product.

Veneer

Sliced Veneer

Pictures needed

Veneer can be sliced or rotary peeled. Veneer is sliced either from lumber or from half- or quarter-logs. Only the best quality logs (straight, mature, figured, free or nearly free of defect) are sliced as the resulting veneer generally goes into high-end applications such as architectural paneling, custom casework and furniture, and so forth.

Logs or lumber that is sliced such that the face of the veneer is tangential (or nearly so) to the growth rings is quarter-sliced. Veneer that is sliced in such a way that the face is perpendicular (or nearly so) to the growth rings is plain-sliced. The two types of grain orientation result in different appearances, with quarter-sliced material having a clean, linear look and plain-sliced a “cathedral” of “flame” pattern. Because sliced veneer can be sequenced on panels (i.e. successive leaves of veneer that come from a single log can be laid up side by side), the graining can be consistent and matching throughout an interior. This is not generally done with flooring that uses sliced veneer as a wear layer. 

Rotary Veneer

Pictures needed 

Veneer can be rotary peeled or sliced. Rotary veneer is peeled from whole logs. The log is placed on a machine that is basically a large lathe and spun at high speeds before engaging with a sharp knife that runs the length of the log and ‘peels’ the veneer away in a contiuous sheet until all that remains is a core. The graining of peeled veneer tends to be wild and random (in flooring, it most resembles plain-sawn wood [link]). While it is the most efficient way to produce veneer, because of its wild graining, rotary veneer is rarely used in architectural paneling.