How Wood Floors Are Made: Timber and Lumber

Kim Wahlgren Headshot
Hf 0199 22 Im1

Hf 0199 22 Im1

When you are out on the job, do you ever stop during installation to think about all the steps the wood flooring has gone through to make it to your job site. Although it's not a relatively complicated product, the process of creating wood flooring begins many months or even years before the wood is milled into a flooring profile and installed in someone's home. Years of forestry management and the work of loggers and sawmills bring the lumber to a point where it can become wood flooring.

Into the Woods

These days, most lumber comes from carefully managed forests. Opinions vary greatly on how hardwood lumber should be harvested. The methods fall roughly into four categories: selection, shelter-wood, group selection or clear-cut. What method is used depends mainly on the opinion of the forest manager.

A trained tree marker designates this tree for removalA trained tree marker designates this tree for removal

Proponents of single-tree selection choose their method based on the species that they are trying to establish and the amount of light these species need in order to grow well. Species such as sugar maple and beech are "tolerant" hardwoods, meaning that they will grow in the shade of other trees. Such trees can be managed by selective harvesting, in which enough trees are harvested so that the forest canopy is opened up to allow about 30 percent of the light to reach the ground. For "mid-tolerant" species such as oak, yellow birch, black cherry and ash, shelter-wood harvesting proponents open up the canopy more, to about 40 percent. People using these methods also use clear-cutting for species such as white birch, aspen or poplar, all of which do not grow well in the shade of other trees.

Logs are dragged out of the forest using a skidderLogs are dragged out of the forest using a skidder

Selective and shelter-wood harvesting involve single-tree selection; that is, before the trees are cut, an inventory is made of the forest tallying species, size and quality. Their information is then compiled, and a prescription for cutting that forest is formulated. Trained tree markers then paint individual trees for removal according to the forest prescription.

Until about 25 years ago, "logger's choice" was sometimes used as a sort of single-tree selection, meaning that the loggers would simply go in and cut the best trees. Although that still occurs today, some managed forests use reverse-high-grade operations, taking out only the poor-quality stock. The best quality trees remain as the future growing stock, just as a garden of vegetables is thinned to produce the best results, and the cut trees allow light to reach the young seedlings and saplings. Proponents of this method say that it results both in better-quality and faster growing forests for the future.

The selectively harvested area on the left shows the difference in light levels as contrasted with the unharvested area on the right.The selectively harvested area on the left shows the difference in light levels as contrasted with the unharvested area on the right.

With this process, the treetops are cut off onto the forest floor, making the log easier to pull out of the forest with smaller equipment. It also helps avoid the damage branches would do to the future growing stock as they were dragged out of the forest. Additionally, the treetops and debris that are left behind benefit the smaller animals of the forest while returning nutrients to the forest floor.

Other forest managers take a drastically different view. They prefer the cutting method of group selection, which is essentially patches of clear cutting that can range in size from 1 to 10 acres. It gives managers the advantages of clear cutting without the unsightly result of a large clear cut. With this method, managers cut down areas of timber that are undesirable or understocked, as well as some areas of mature timber. If they want to cultivate a certain specie, they may replant it in the cut area. More likely, they leave the area to do what they say hardwood does readily — regenerate itself. The natural regeneration can occur from root sprouts, stump sprouts or seedlings.

Seen from a distance, the completed selection harvest across the lake is difficult to detect.Seen from a distance, the completed selection harvest across the lake is difficult to detect.

Group selection proponents say that selective cutting does not work in a hardwood forest, because the remaining trees develop epicormic branches — areas where new branches sprout out from the trunk. These new branches create a knot within the timber and degrade the lumber from that point on. Advocates of group selection also point out that hardwoods tend to have large crowns, which cause excessive damage to surrounding trees as the single tree is felled.

Whichever method is used, the loggers go into the woods with a careful plan of exactly what they are cutting. Large machines generically referred to as feller bunchers do most of the cutting, with chain saws also used for the larger trees. Although some horse logging is still done, most of the logs are pulled out of the forest with a skidder, which pulls out the logs using steel cables and a winch.

In the United States, the U.S. Forest Service has grades for logs: Veneer, One, Two and Three, while in Canada the log grades are Grade 1 and Grade 2. Graders look for visible defects on the tree, such as areas where branches had been cut or where there is rot, and grade accordingly. The Veneer grade is the highest quality. One-grade logs will become the highest grades of lumber, Two-grade become a medium grade of lumber, and Three-grade logs eventually will go to uses such as wood for pallets. All grades of lumber come out of each of the log grades, although the percentage of each grade of lumber changes as the log grade goes down.

Logs head into the mill on the infeed deck.Logs head into the mill on the infeed deck.

Into Production

At the sawmill, the first step for the logs is the debarker. Essentially like a giant pencil sharpener, the debarker takes the bark off all sides of the log in a single process. The shaved logs are then rolled on the carriage, where a log turner turns the log so that the best face can be selected to produce the best yield. Many mills have a computer with laser optics to select the first cut of the log, and a slab is cut off there, resulting in the log's first flat side. The cut slab may go into a chipper, or in high-production mills this slab may go to another saw, a horizontal resaw.

With one flat side, the log is then cut into long slices. As the cutting approaches the heart of the log, the log is turned (typically 180 degrees) and cut from a new direction. This process is either accomplished by a band mill, which is essentially like a large band saw, or by a circle mill, which has a large blade and is similar in function to a circle saw.

After the debarker, a slab is cut off one side of the log.After the debarker, a slab is cut off one side of the log.

These long boards of the log still have rough edges and some bark left on them, so they are taken off the carriage and head to the edger, which trims most of the wane (where lumber doesn't reach the full width of a board) and bark off. Next a double-end trim saw takes off defects from the ends of the board such as bark ends and splits, and may cut board to a desired length.

This clean lumber is of varying dimensions. It may be anywhere from 1 to 4 inches thick, 4 to 16 feet long, and a minimum of 3 inches wide, going up to as wide as the saw is capable of cutting.

Making the Grade

Now the lumber is ready for grading. Lumber grades in the United States and Canada are determined by the National Hardwood Lumber Association, based in Memphis, Tenn. (The Canadian Lumbermen's Association adopts the NHLA grades verbatim and distributes the rules in Canada on behalf of NHLA.) Although NHLA's grades may vary slightly for different species, the standard grades range from highest to lowest quality: FAS, FAS One Face (F1F), Select, No. 1 Common, No. 2A Common, No. 3A Common, No. 2B Common,No. 3B Common, and Wormy. Although lumber and flooring grade names are similar or identical, the grade of lumber does not dictate the grade of flooring. Thus, No. 1 Common lumber will not necessarily produce No. 1 Common flooring.

A band mill cuts the log into long boards.A band mill cuts the log into long boards.

FAS and F1F are used for high-end work, such as specialty millwork. No. 1 Common is the standard used for the furniture and cabinet industries. By far, the most often used lumber grades for hardwood floors are No. 2A Common and No. 3A Common. However, some flooring manufacturers, especially plank producers (who need to maintain quality across a larger area of flooring), may use No. 1 Common. Additionally, market demand for No. 2A Common and No. 3A Common has continued to increase in recent years, as cabinet and furniture makers move into a lower grade of lumber. This has caused some flooring manufacturers to buy No. 1 Common in order to maintain a lumber supply.

Bound for Flooring

Now separated by grade and species, the lumber heads to the flooring mill, ideally within days of being sawn. There it is stacked with sticks — wooden strips placed between layers of lumber to permit air circulation — and either air dried or predried. If it is air dried, it can take a matter of months, depending on the wood's moisture content and the weather. Predrying the lumber, in which it is stacked in large, atmospherically controlled buildings, can result in fewer moisture defects such as checking and can take a shorter period of time. In areas of the South, however, air drying is often faster than predrying.

An optimizing edger determines what the width of the board will be.An optimizing edger determines what the width of the board will be.

After the initial drying, the moisture content of the wood is usually in the low 20 percent range before it heads into the kilns, essentially large ovens that remove most of the moisture from the wood and sterilize it from insects and other contaminants. The kiln temperature ranges anywhere from 100 to 108 degrees Fahrenheit, with dry kiln schedules typically ending between 160 and 180 degrees Fahrenheit. Kiln types vary, with dehumidification kilns, steam kilns and dry heat kilns all used. The most technologically advanced kilns are carefully controlled by computers that continually measure temperature, humidity, air flow, vent capacity and moisture content at points throughout the kiln. At the end of its time in the kiln, the lumber has a specific moisture content of, for example, 7 percent.

To cool out, the stacked lumber is placed in cooling sheds for the necessary period of time; then it is ready to head into the flooring mill.

 

Stacked lumber is air dried before heading to the kiln.Stacked lumber is air dried before heading to the kiln.

 

Kilns dry and sterilize the lumber.Kilns dry and sterilize the lumber.

 

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