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Understanding Hardwood Floors

19 min read
Published on August 14, 2020

Understanding Hardwood Floors

Terminology

The Character of Wood

Heartwood

Sapwood

Wood Grain and Texture

Types of Saw Cut

Moisture Content and Dimensional Stability

Wood comfort level

Moisture Meter Testing

Hardness

Durability

Machining

Nailing

Sanding

Choices in Wood Flooring Wood selection 

Cleaning suggestions 

Wood Patina

Image
room with solid hardwood flooring
Virginia Mill Works Misty Point Distressed Solid Hardwood Flooring, 3.5 in. Width

 

The Character of Wood

Wood is a dynamic medium. Like all organic materials, it has character and changes over time. Because of its 'personality', wood should be treated with understanding and a certain amount of care. For wood flooring professionals, knowing about the properties of wood in general, as well as those of individual wood species such as workability, is critical to proper installation. For consumers, it is important to have realistic expectations about how wood will perform. Wood flooring manufacturers do not warrant against surface denting or scratches. Color changes can be dramatic for all woods especially for bamboo and the exotics.

As a flooring material, wood is superior to vinyl or carpet, both practically and aesthetically. A solid wood floor is more than a covering; it adds strength and stability to the floor system. A one-inch thickness of wood has the same insulating value as 15 inches of concrete. Wood is durable and long lasting, occasional sanding and refinishing essentially results in a brand-new floor. Wood floors do not retain mildew or absorb dust, simplifying cleaning and is perfect for those with allergen concerns

Perhaps the most appealing characteristics of wood flooring are its attractive appearance and natural warmth. A beautiful wood floor can enliven a drab room, enhance any architectural style, complement furniture and design schemes, and add value to any home or building.

A combination of qualities should be considered when selecting a species for flooring: appearance related attributes such as texture, grain, and color as well as mechanical properties like dimensional stability, durability, workability, and ease in finishing; and finally, availability and cost. Many different factors, from the nature of the living tree to the way the lumber is sawed, affect the way the finished floor will look.

HEARTWOOD

Heartwood is the older, harder central portion of a tree. It usually contains deposits of various materials that frequently give it a darker color than sapwood. It is denser, less permeable and more durable than the surrounding sapwood.

SAPWOOD

Sapwood is the softer, younger outer portion of a tree that lies between the cambium (formative layer just under the bark) and the heartwood. It is more permeable, less durable and usually lighter in color than the heartwood, so this is the reason why certain species can have grater variance in color right out of the box!

The relative amounts of heartwood and sapwood in a flooring batch may affect the way it accepts stain and finish and, therefore, the finished appearance of the floor. In general, quartersawn and riftsawn flooring which contain less sapwood than plainsawn flooring and will tend to have a straighter grain and more uniform appearance. Interestingly, an individual board that may taper from one end to the other is a result of a board having both quarter-sawn on one end and plain-sawn on the other. This is not a manufacture's defect but a wood property. Boards 1/8" narrower than surrounding boards should be culled out and set aside. These planks can be used on the same row or used in the last row installed. Heartwood is also more dimensionally stable than sapwood, so flooring with a high percentage of heartwood will shrink and swell less than flooring that is mostly sapwood.

Wood Grain and Texture "Grain" and "texture" are loosely used to describe similar properties of wood. Grain is often used in reference to annual growth rings, as in "fine" or "coarse" grain. It is also used to indicate the direction of fibers, as in straight, spiral, and curly grain. The direction of the grain, as well as the amount of figuring in the wood, can affect the way it is sanded and sawed. Grain is also described as being either "open" or "closed", referring to the relative size of the pores, which affects the way a wood accepts stain and finishes.

Texture usually refers to the finer structure of the wood, rather than to the annual rings. It is sometimes used to combine the concepts of density and degree of contrast between spring wood and summer wood in the annual growth rings.

Terminology and Types of Saw Cut

Annual rings : Most species grown in temperate climates produce visible annual growth rings that show the difference in density and color between wood formed early and that formed late in the growing season. The inner part of the growth rings, formed first, is called spring wood the outer part, formed later in the season, is called summer wood.

Spring wood : is characterized by cells having relatively large cavities and thin walls. Summer wood cells have smaller cavities and thicker walls, and consequently are more dense than those in spring wood. The growth rings, when exposed by conventional sawing methods, provide the grain or characteristic pattern of the wood. The distinguishing features among the various species result in part, then, from differences in growth-ring formation. And within species, natural variations in growth ensure the unique character and beauty of each piece of wood.

Figure : The pattern produced in a wood Surface by annual growth rings, rays, knots, and deviations from regular grain.

Medullary Rays : Medullary rays extend radically from the core of the tree toward the bark. They vary in height from a few cells in some species, to four or more inches in the oaks; they're responsible for the flake effect common to the quartersawn lumber in certain species.

Tangential Grain : Usually called flat grain; easily recognized by its parabolic (arched) effect. Lumber is considered flat-grained when the annual growth rings make an angle of less than 45 degrees with the wide surface of the board.

Radial Grain : Known as vertical or edge grain; generally more dimensionally stable than flat grain - that is, vertical-grain boards are less likely to expand or contract in width with changes in moisture. Lumber is considered vertical-grained when the annual growth rings make an angle of 45 to 90 degrees with the wide surface of the board.

Interlocked Grain : Grain in which the fibers may slope in a right-handed direction several years, then in a left-handed direction for several years, back to right-handed, and so on. A high degree of interlocked grain may make a wood difficult to machine.

(Note: In hardwoods, plainsawn lumber generally contains mostly flat-grained wood, while quartersawn lumber is nearly all vertical-grained. In softwood lumber the terms flat-grained and vertical-grained are used instead of the terms plainsawn and quartersawn, respectively. Lumber is either plainsawn, quartersawn or riftsawn.

Plainsawn lumber is obtained by making the first saw cut on a tangent to the circumference of the log and remaining cuts parallel to the first. Since most of the lumber produced by plainsawing is flat-grained, with some vertical-grained wood included, plainsawn lumber will tend to contain more variation within and among boards than quartersawn lumber, in which nearly all of the wood is vertical-grained. Also, since flat-grained wood is less dimensionally stable than vertical-grained, plainsawn lumber will tend to expand and contract more across the width of the boards than quartersawn lumber.

Other physical differences to consider when choosing plainsawn lumber rather than quartersawn:

  • Figure patterns resulting from the annual rings and some other types of figures are usually brought out more conspicuously by plainsawing.
  • Shakes and pitch pockets, when present, extend through fewer boards.

In quartersawing, lumber is produced by first quartering the log and then sawing perpendicular to the growth rings. Quartersawing produces relatively narrow boards, nearly all vertical-grained, and creates more waste, making quartersawn lumber more expensive than plainsawn. However, much quartersawn wood is obtained by cuffing the vertical-grained wood that naturally results from plainsawing.

For reasons other than cost, most people prefer quartersawn wood, although some people favor the variety in figuring produced in plainsawing.

 

Other physical factors to keep in mind when choosing quartersawn lumber over plainsawn:

  • It twists and cups less.
  • It surface-checks and splits less during seasoning and in use.
  • Raised grain produced by separation in the annual growth rings does not appear as pronounced.
  • It wears more evenly.
  • Figuring due to pronounced rays, interlocked, and wavy grain are brought out more conspicuously.
  • Sapwood appears only at the edges, and is limited to the width of the sapwood in the log.

Riftsawing is similar to quartersawing, with many of the same advantages and limitations. It accentuates the vertical grain and minimizes the flake effect common in quartersawn oak. The angle of the cut is changed slightly so that fewer saw cuts are parallel to the medullary rays, which are responsible for the flake effect. Riftsawing creates more waste than quartersawing, making it generally more expensive.

Moisture Content and Dimensional Stability

Moisture plays a large part in how wood behaves, both during the machining process and after installation. Installers would do well to study moisture's effect on wood in some detail: however, a brief discussion is worthwhile here.

Moisture content is defined as the weight of water in wood expressed as a percentage of the weight of oven-dry wood. Weight, shrinkage, strength and other properties depend on the moisture content of wood.

Wood is dimensionally stable when the moisture content is above the fiber saturation point (usually about 30 percent moisture content). Below that, wood changes dimension when it gains or loses moisture.

The ideal moisture content for flooring installation can vary from an extreme of 4 to 18 percent, depending on the wood species, the geographic location of the end product, and the time of year. Most oak flooring, for example, is milled at 6 to 9 percent. Before installation, solid wood flooring should be  acclimated to the area in which it is to be used, then tested with a moisture meter to ensure the proper moisture content (Note: Engineered flooring tends to be more dimensionally stable than solid flooring and is highly recommended for Radiant and glue down installations).

Different woods exhibit different moisture stability factors, but they generally shrink and swell the most in the direction of the annual growth rings (tangentially), about half as much across the rings (radically), and only slightly along the grain (longitudinally). This means that plainsawn flooring will tend to shrink and swell more in width than quartersawn flooring and that most flooring will not shrink or swell much in length.

The individual species descriptions that follow include an indication of dimensional stability, from below average to excellent, as well as a comparison to red oak. For example, mesquite is rated as excellent, with notation that it is 65 percent more stable than red oak - that is, mesquite is likely to shrink or swell 65 percent less. The percentages noted are based on comparing a factor called the dimensional change coefficient of each species with that of red oak. Red oak was chosen as the benchmark because of its widespread familiarity and use in the flooring industry.

WOOD COMFORT LEVEL

Wood flooring will perform best when the interior environment is controlled to stay within a relative humidity range of 30 to 50 percent and a temperature range 60 to 80 degrees Fahrenheit. Fortunately, that's about the same comfort range most humans enjoy. The chart below indicates the moisture content wood will likely have at any given combination of temperature and humidity. Note that equilibrium moisture contents in the recommended temperature/humidity range (shaded area) coincide with the 6 to 9 percent range within which most hardwood flooring is manufactured. Although some movement can be expected even between 6 and 9 percent, wood can expand and shrink dramatically outside that range.

MOISTURE CONTENT OF WOOD AT VARIOUS TEMPERATURES AND RELATIVE HUMIDUTY READINGS

Chart taken from Woodhandbook: Wood has an Engineering Material, (Agriculture Handbook 72), Fores products laboratory, U.S. Department of Agriculture.

Moisture Meter Testing

Know the acceptable moisture levels, correct before installation, create a paper trail by documenting your results.The wood subfloor must not exceed 12% moisture content. Measure moisture content of both subfloor and wood flooring to determine proper moisture content with a reliable wood moisture meter. The difference between the moisture content of the wood subfloor and the wood flooring must not exceed 4% or 2% for 3" and wider boards.

Concrete Slabs

Solid flooring can be installed over concrete once the appropriate nailing surface has been installed. The concrete must be of high compressive strength. All concrete should be tested for moisture content Visual checks are not reliable.

NOTE: Test several areas, especially near exterior walls and walls containing plumbing.

A "DRY" SLAB, AS DEFINED BY THESE TESTS CAN BE WET AT OTHER TIMES OF THE YEAR. THESE TESTS DO NOT GUARANTEE A DRY SLAB. ALL CONCRETE SLABS SHOULD HAVE A MINIMUM OF 6 MIL POLY FILM MOISTURE BARRIER BETWEEN THE GROUND AND THE CONCRETE.

Cement installations require moisture barriers, see our "FLOORING 101" for details.

Hardness

Probably the most important strength property for wood used in flooring applications is its side hardness, also known as Janka hardness. Side hardness represents the resistance of wood to wear, denting, and marring. It is measured by the load required to embed a 0.444 - inch steel ball to one-half its diameter in the wood. The higher the number the harder the wood. Janka hardness ratings are generally based on an average of tests on both tangential and radial (plainsawn and quartersawn) samples.

Below are listed the relative hardness for numerous wood species used in flooring. Although this is one of the best methods to measure the ability of wood species to withstand indentations, it should be used as a  general guide when comparing various species of wood flooring. The construction and finish also play an important role in the durability and ease of maintenance of any wood floor.

Durability -Taber Test

The Taber Test is an abrasion testing method that was designed to measure the abrasion resistance of protective floor finishes. Flooring squares are secured to a turntable and then weighted with sandpaper. The turntable is rotated, causing the sandpaper to wear against the finish.

Finish warrantees are established by Taber testing results.

In blind "Taber" Testing by an independent laboratory, our Bellawood came out on top with an extraordinary Taber Rating of over 1600!

Machining

The workability of a wood depends on several factors, including density, extent of interlocked or variable grain, hard mineral deposits, and tensions in wood that may cause fibrous and fuzzy surfaces. The degree of checking and separation present will also affect machining ease.

Interlocked grain is characteristic of many tropical species and causes problems in planning quartersawn boards unless feed rates, cutting angles, and sharpness of knives are carefully controlled. Hard deposits in the cells, such as calcium carbonate and silica, may have a pronounced dulling effect on cutting tools. This effect generally increases as wood is dried to normal working requirements.

Nailing

When nailing some of the denser woods with air nailers, installers may encounter splitting tongues, as well as failure to secure the fastener even after repeated attempts. This can sometimes be corrected by changing the angle of the nails point of entry. On certain exceptionally dense species, pilot holes may have to be drilled and the flooring will be hand nail. Blunting the ends of some fasteners may also help prevent splitting. Though dense, heavy woods normally offer higher nail-withdrawal resistance, less dense species allow the use of more and larger diameter fasteners to compensate for their lower holding ability.

IT IS EXTREMELY IMPORTANT TO USE THE PROPER ADAPTERS AS WELL AS STAPLES OR CLEATS. IMPROPER FASTENERS, MACHINES AND AIR PRESSURE CAN CAUSE SEVERE DAMAGE. THE MANUFACTURER OF FLOORING PRODUCT IS NOT RESPONSIBLE FOR DAMAGE CAUSED BY USE OF IMPROPER TOOLS OR MISUSE.    

  PRE-DRILLING AND HAND NAILING MAY BE RECOMMENDED FOR THE HARDER 3/4" EXOTICS LIKE BLOOD WOOD, BRAZILIAN CHERRY, ROSE WOOD, BRAZILIAN WALNUT, BRAZILIAN TEAKS, AND MAHOGANY TO PREVENT TONGUE FRACTURE OR SURFACE DIMPLING COMMON TO NAILING MACHINES. THE 18 GAUGE CLEAT FLOORING NAILERS ARE RECOMMENDED FOR THE DENSER EXOTIC FLOORS.    

THE 3/8" EXOTIC MATERIALS REQUIRE A STRONG THINNER TYPE 18 GAUGE CLEAT NAIL AS WELL.           

If USING A STAPLER FASTENER FOR 3/8" SOLIDS, INSTALLER SHOULD VERIFY STAPLE HOLD AND ENSURE AGAINST TONGUE FRACTURE    STAPLES SHOULD BE 3/16"or 1/4"CROWN 1"TO 1-1/4" IN LENGTH

Typical 5/16" or 3/8" Engineered stapler

Sanding

Some wood species are highly resinous and tend to clog sandpaper. When working with such species, it may be necessary to use a coarser grit of sandpaper than normal, or to change the sandpaper more often than with other species.

Also, the wood dust created by sanding some species tends to cause an allergic reaction in some people. This is more likely to occur with imported species than with domestic. However, even North American oak has been known to cause a skin rash or respiratory difficulties in some people. Where applicable, known tendencies to cause allergic reactions are noted.

As a precaution, flooring mechanics should wear long sleeves, dust masks, and eye protection when sanding.

Choices in Wood Flooring

Wood flooring is available in a number of sizes and make-ups, each offering its own distinct advantages. People are often surprised by the limitless choices that wood flooring affords them. Today's wood flooring is right for virtually every room. Choosing the right kind and style of wood flooring is not hard if you are familiar with several industry terms.

Unfinished wood flooring

Unfinished flooring is a product that must be job-site sanded and finished after installation. If you want a custom stained hardwood floor, or a wood floor to match existing trim, a job-site finish is your answer. Job-site finish means you start with a bare (unfinished) hardwood floor and than the floor is sanded, stained, and finished in the home. The other advantage of a job-site finish is, if you are concerned with uneven heights between planks, the sanding process will smooth out the floor. Be warned though, this can be quite a mess and the process does take several days.

Job-site hardwood floor finishing methods include:

  • Water Based Urethane - Water is used as part of the chemical make up of the polyurethane finish.
  • Solvent Based Urethane - Oil is used as part of the chemical make up of the polyurethane finish.
  • Moisture Cured Urethane - A similar chemical make up as solvent based urethanes, but this finish needs the humidity (moisture) in the air to cure.

Pre-finished wood flooring

Pre-finished flooring is factory-sanded and finished flooring that only needs installation.

 

Finishes for Pre-finished Wood

  • Oil-modified urethane -is generally the most common surface finish and is easy to apply. It is a solvent-base polyurethane that dries in about eight hours. This type of finish ambers with age.
  • Moisture-cure urethane -is a solvent-base polyurethane that is more durable and more moisture resistant than other surface finishes. Moisture-cure urethane comes in non-yellowing and in ambering types and is generally available in satin or gloss. These finishes are extremely difficult to apply, have a strong odor and are best left to the professional.
  • Water-based urethane -is a waterborne urethane that dries by water evaporation. These finishes are clear and non-yellowing. They have a milder odor than oil-modified finishes have and they dry in about two to three hours. Water-based urethanes are generally more expensive.
  • Aluminum Oxide Finishes - The newest in wood floor finishes offers a long lasting more durable coating than past wood floor finishes. These finishes carry long wear warranties, and is the latest trend by major pre-finished wood floor manufacturers.

Solid Tongue & Groove Design

Solid wood flooring is made from complete lumber. It is available in unfinished and pre-finished. Also available as planks

Engineered wood flooring

Engineered wood is produced by bonding layers of veneer and lumber with an adhesive. Available as a square or V edge. These products are designed to be more dimensionally stable and are ideal for Radiant heated installations. Available as a staple-down, nail-down, glue-down or floating applications above grade, on grade, or below grade, including basements and humid climates

Square Edge:

The edges of all boards meet squarely creating a uniform, smooth surface that blends the floor together from board to board. The overall look of this floor gives a contemporary flair and formal feeling to the room.

Eased Edge or Micro Bevel:

Each board is just slightly beveled. Some manufacturers add an eased edge to both the length of the planks as well as the end joints. Eased edges are used to help hide minor irregularities, such as uneven plank heights. Eased edge is also called microbeveled edge.

Beveled or V Edge:

These products have a very distinctive groove in them. Beveled edge planks lend themselves to an informal and country decor. With the urethane finishes applied at the factory today, the beveled edges are sealed completely, making dirt and grit easy to be swept or vacuumed out of the grooves.

Wood selections

To begin with, you need to look at where you plan on installing your new wood floor. There are limitations on where some wood floors can be installed. This is especially true for the 3/4" solid wood floors. Solid hardwood floors are more susceptible to moisture and are generally not recommended for basements, or installing directly onto a concrete slab. To help you determine where these floors can be installed you need to understand the different grade levels, see the diagrams.

  • Above Grade - The portion of a building that is above ground level-i.e. crawlspace under a subfloor. All hardwoods can be installed.
  • On Grade - The portion of a building that is on ground level-i.e. Wood or cement. solid wood and engineered floors work well over on grade wood subfloors. For on grade concrete floors engineered wood floors work best.       
  • Below Grade - The portion of a building that is below ground level -i.e. A basement. Recommended floors are Engineered or Floating, (Use of moisture barriers recommended)


Cleaning suggestions The character and elegance of a hardwood floor makes it a favorite among homeowners. In addition, if you have come here you are probably more than just mildly interested in hardwood.

The point of this section is that, if you're seriously considering hardwood floor covering as a solution for the way you live, the way you treat that floor is important.

Wood is a natural, beautiful and timeless design and decorating element.

So check out the hardwood floor care tips below and be prepared to have your family and friends "check out" your new hardwood floor with praise. For years to come.

Protect your floors

Place walk off mats or area rugs at each entryway to collect dirt and grit that might be tracked in. These tiny particles act like sandpaper and will scratch your floor.

Be sure to avoid using rubber-backed or non-ventilated mats or rugs as they can damage your floor. Instead use mats or rugs made especially for hardwood floors and remember to shake them out regularly.

In addition to entryways, remember to place mats in any areas where water may be splashed, such as near a kitchen sink.

Buy a good quality broom and sweep your new floor regularly to pick up grains of dirt, dust and other particles.

A vacuum cleaner, without a beater bar, can be helpful in between planks and other hard to reach areas. Once dirt and grease are gone, buffing can help restore the luster of your hardwood floor.

Cleaning techniques vary depending on the installation and finish of your hardwood floor.

For "Finish in Place" hardwood floors, we recommend using an 8"x14" terrycloth mop with a rotating head that makes cleaning corners, under cabinets and along base boards an easy task. Manufacturers of "Prefinished" hardwood floors recommend their own specific products designed for their floors routine maintenance. Use products safe for your urethane finishes.

Hardwood dos and dont's.

All floors with a urethane finish should never be waxed and require cleaners that won't leave a film or residue.

A hardwood floor cleaner is useful in removing occasional scuffs or heel marks. Merely spray some cleaner on a cloth and lightly rub the stained area. Sticky spots can be cleaned with a damp towel or sponge.

Do not use ammonia, vinegar, Windex type cleaners or oil soaps on a pre finished wood floor, as they will dull the finish and performance of your floor. These products will also affect the ability to recoat your floor later. Since wood naturally expands when it is wet, never wet mop or use excessive water to clean your floor. Large amounts of water can cause the wood to swell and may cause your floor to crack or splinter. Being a natural product, hardwood will expand and contract due to moisture level changes. Minimize water exposure to hardwood floors and clean up spills as soon as they happen.

Cover furniture and table legs with protectors to guard your floor against damage. Take care when moving heavy objects across your floor to avoid scuffing.

Stiletto heels can cause dents and scratches not covered by your warranty. Love your pet by regularly trimming their nails or claws to avoid scratches on the hardwood floor. The point here is to be cautious of sharp objects that may scratch or damage the floor. The regular cleaning and periodic professional maintenance of your hardwood flooring will insure a home and lifestyle of beauty and comfort for years to come.

Wood Patina

       Wood products can be dramatic in appearance, especially the exotics. Only factory made products such as tile, vinyl, wallpaper can have uniformity of color. Keep in mind that wood is a natural product and that no two floor boards will be identical. Variations in appearance are completely normal. As your floor ages, color change or "patina" can occur. This process can be rapid the first 3 months, less in 6 months, then finishing off in about I year. Moving the furniture around helps to even out this condition. Avoid area rugs the first 3 months. Whether finished or unfinished, all wood changes color over time due to oxidation and when exposed to light. Some species darken in color over time, while others tend to lighten. There is no known set value for "color fastness" of a species, so contractors and or customers should be aware of this normal condition. Certain species, including American cherry, Koa, Brazilian cherry, and many imported species have this tendency to change in color. Some color change is to be expected for all species and a drastic change can be expected for some. All hardwood floors will fade, darken or change shades over time. Exposure to sunlight will greatly increase this process. Window treatments are recommended, as well as rotating area rugs and furniture regularly to allow floors to age evenly from UV exposure.     

When installing, select boards from several boxes. Working from one box at a time can create poor color grouping or placement of any flooring. Any extreme color difference can be culled out and simply replaced with the 5-10% overage you should have on hand.

Our LL Flooring customer Service Department is ready to help you with your selection process. The Technical and Installation Department can also help before, during and after your installation visit your local LL Showroom or chat online for assistance.

Customer Service and Technical & Installation Departments

04.2019