History

The Character of Wood

Wood grain and texture

Types of Saw Cut

Mechanical Properties

Choices in Wood Flooring

Finishes

HISTORY

In the Middle Ages wood flooring was introduced. Throughout the world, many examples exist, of floors that have been in daily use for the last 800 years. With the early machine years, came finer milling and the ornate parquets - many patterns still in use today.

The physical properties of wood that attract us are:

1. Natural warmth - to the touch; wood insulates
2. Workability, easily shaped with simple tools
3. Infinite variety; no two trees, or even pieces from the same tree, are alike
4. Strength-to-weight ratio for bridges, boats, homes, furniture
5. Flexibility; watch even huge trees bend before the wind
6. Fire protection; wood chars and therefore burns slowly, doesn't melt or crumble
7. Natural Colour, through wood's ability to receive many types of stains and finishes.
   

In the late 1800's the development of steam and electric power produced the industrial age and coincidentally growth in the nation's need for better housing. The wood floor industry in our country was born to meet this need. Early manufacturers utilized oak because of availability and related low cost, strength and beauty. It machines well on high- speed equipment. Its flexibility provides comfort under foot. Oak floors became the standard floor for American housing. Today, more people are looking into exotic solid hardwood from Asia. Exotic wood gives an elegant tropical forest touch. Exotic wood flooring adds extraordinary glow, warmth richness and beauty to the working or home living environment.

Most manufacturers are located in our southern states to be near a plentiful raw-material source and to gain the climatic advantage to air day the raw lumber. Generally, the flooring mill was dependent on nearby timber stands where trees were felled, cut to lengths, sawed by portable mills into rough boards and stacked in fields to dry for four to six months. The rough boards were then hauled by horse-drawn wagon to the flooring mill for kiln drying and finish manufacture. As trucks and roads were developed, the radius around the mill for trees or raw boards expanded to about 75 miles.

A giant step was taken with the development of elastomeric adhesives. Wood floors could now be glued down to concrete, plywood, and old floors, really almost anywhere in a home, office, apartment or commercial building. Coincidentally, slab housing had grown to more than 40% of the market.

Wood was back! But, in a different form. Years before, when wood had been used throughout all project housing, carpet was a special floor only for the wealthy in the big house on the hill. In the 70's carpet was everywhere and in the least expensive homes while hardwood floors found their way into the fine higher priced custom market.

A 180-degree turnaround. Carpet became a commodity; hardwood floors became the special surface for the special rooms. Area rugs flourished, naturally over a wood floor. A myriad of new patterns, textured surfaces and new finishes continued the surge in wood. The textures and impregnated wood resulted in more wood being specified in commercial high-traffic public areas. Imported flooring began to find a place in the market. Both carpet and resilient industry manufacturers copied the "wood-look" in their products, the highest form of flattery.

Wood floors were in use everywhere. Not as a low-priced commodity covering in every room, but as a high-priced, high style, special area surface.

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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, is critical to proper installation. For consumers, it's important to have realistic expectations about how wood will perform. Most wood used for flooring is essentially a by-product of more expensive wood-consuming industries (furniture manufacture, for example), so it is usually not the highest grade of lumber. However, it is quite economical in comparison.

As 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 don't retain mildew or absorb dust, simplifying cleaning.

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 colour as well as mechanical properties like dimensional stability, durability, machinabilty, and ease in finishing; and finally, availability and cost.

Properties affecting appearance: 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

A. Heartwood

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

B. 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 colour than the heartwood.

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, quarter-sawn and rift-sawn flooring which contain less sapwood than plain-sawn flooring (Refer to Fig. 2 and Fig. 3), and will tend to have a straighter grain and more uniform appearance. 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.

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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.

Some Wood Grain Terminology

Fig. 1

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

2. 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 quarter-sawn lumber in certain species.

3. 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.

4. 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.

(Note: In hardwoods, plain-sawn lumber generally contains mostly flat-grained wood, while quarter-sawn lumber is nearly all vertical-grained. In softwood lumber the terms "flat-grained" and "vertical-grained" are used instead of the terms "plain-sawn" and "quarter-sawn", respectively. See "Fig. 2 and Fig. 3" below)

5. 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.

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TYPES OF SAW CUT

Lumber is plain-sawn, quarter-sawn or rift-sawn.

Fig. 2

Fig. 3

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

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

For reasons other than cost, most people prefer quarter-sawn wood, although some people favour the variety in figuring produced in plain sawing.

Other physical factors to keep in mind when choosing quarter-sawn lumber over plain-sawn:

• 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.
  

3. Rift sawing is similar to quarter sawing, with many of the same advantages and limitations. It accentuates the vertical grain and minimizes the flake effect common in quarter-sawn 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. Rift sawing creates more waste than quarter-sawing, making it generally more expensive.

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MECHANICAL PROPERTIES

A. 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.)

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 plain-sawn flooring will tend to shrink and swell more in width than quarter-sawn 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.

B. Hardness and Durability

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. The load required to embed a 0.444 - inch steel ball to one-half its diameter in the wood, measures it. Janka hardness ratings are generally based on an average of tests on both tangential and radial (plain-sawn and quarter-sawn) samples.

Hardness by Species

C. 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 forest species and causes problems in planning quarter-sawn or rift-sawn 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.

D. Nailing

When nailing some of the denser woods with hand or 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 nail’s point of entry. On certain exceptionally dense species, pilot holes may have to be drilled to ease nailing. Blunting the ends of 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.

E. 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 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.

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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.

A. Unfinished Wood Flooring

Unfinished flooring is a product that must be job-site sanded and finished after installation.

B. Pre-finished Wood Flooring

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

C. Solid Wood Flooring

Solid wood flooring is completely lumber. It is available in unfinished and pre-finished. Solid wood flooring is produced in:

• Strip - in thickness of ½” or ¾” in widths of 1-1/2”, 2”, 2-1/4” , 3-1/4” and etc.
• Plank - in thickness of ½” or ¾” and widths of 2-1/4” to 5-1/4”
• Parquet - geometrical patterns composed of individual wood slats held in place by mechanical fastening or an adhesive
  

D. Engineered Wood Flooring

Bonding layers of veneer and lumber with an adhesive produces engineered wood flooring. It is available in pre-finished and unfinished. These products are more dimensionally stable and are ideal for glue-down installation or floating installation above grade, on grade, or below grade, including basements and humid climates. Engineered wood flooring is produced in:

• Strip - thickness of ¼”, 5/16”, 3/8”, ½”, or 5/8” and in widths of 2” and 2-1/4”
• Plank - thickness of ¼”, 5/16”, 3/8”, ½”. or 5/8” and in widths of 3” to 8”
• Parquet - one-piece wood tile available in several sizes and patterns.
  

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FINISHES

Oil-modified urethane is generally the most common surface finish and is easy to apply. It is solvent-base polyurethane that dries in about eight hours. This type of finishes ambers with age.

Moisture-cure urethane is 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 odour 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 odour than oil-modified finishes have and they dry in about two to three hours. Water-based urethanes are generally more expensive.

Aluminium oxide finishes - The newest in wood floor finishes offers a long lasting more durable coating than past wood floor finishes. This finishes carry long wear warranties, and is the latest trend by major pre-finished wood floor manufacturers.

Pre-finished Wood (Standard Abrasion Resistance Hardness Test)

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