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Hardwood Floor Finishing

October 21, 2010

The warmth and rich character of hardwood flooring has helped this floor covering alternative earn unprecedented popularity. Not only do consumers embrace wood flooring for their homes, but it has become increasingly popular in commercial applications as well.

What is it exactly about hardwood floors that make them so appealing?

A number of benefits have contributed to the growth of this estimated $20 billion a year market.

SUSTAINABILITY The environmental benefits of hardwood flooring have played a significant role in its rise as a popular floor covering choice. As consumers place increased importance on green alternatives for their homes and workplaces—even their vacation destinations—they are finding that furnishings made of natural, renewable materials, such as hardwood floors, are ideal choices.

Consumers have learned to look for wood flooring from environmentally responsible suppliers. For example, wood floors certified by the Forest Stewardship Council (FSC) means the wood has been sourced according to responsible forest management practices. Additionally, durable finishes that are easier to maintain means that wood floors can last for 100 years or more—a life-cycle that few products can match.

VARIETY AND BEAUTY Hardwood floors have a natural warmth and timeless beauty that no other floor covering can offer. An abundance of wood species, grains, and color means that hardwood flooring has a versatility to match a multitude of décors. Wood also provides high insulation properties. Consumers can choose from prefinished wood flooring or solid unfinished flooring, which is installed, sanded, stained or sealed, and finished on-site.

UNLIMITED OPTIONS Even when a space is remodeled, hardwood flooring can be changed to match. Wood can be sanded and finished to renew its original look, or stained to change color. Borders and medallions can be added to create pattern and intricacy.

EASY TO MAINTAIN For regular maintenance, hardwood floors require simple sweeping, vacuuming and cleaning with a residue-free hardwood floor cleaner. Periodic recoating can renew the floor to its original sheen (provided the floor is coated before being completely worn through).

ECONOMICAL Hardwood flooring not only increases property value, but it also never goes out of style. Additionally, because of its durability, with proper care, hardwood flooring can last for generations—making for an unparalleled return on investment.

HEALTHIER THAN ALTERNATIVES Hardwood flooring offers a multitude of health benefits. It does not trap dust, allergens and other particulates. Dirt and debris commonly found in carpet and padding, as well as mold and mildew, also are not present. Finally, there's less waste associated with renewing hardwood flooring as compared to replacing carpet that is stained or worn out.

Videos for this CEU

Sponsors Bona have provided three videos to watch to assist you in taling this CEU:

SELECTING HARDWOOD FLOORSWhen selecting hardwood floors, a number of decisions must be made regarding type, wood species, style and grade.

TYPEEngineered prefinished hardwood floors are made of several layers or "plies" that are glued together in a cross-grain construction and feature a factory-applied finish. Oftentimes, faster growing wood is used for the inner plies, which earns engineered flooring an environmental thumbs up.

Engineered floors can be installed below grade and direct to concrete, and they have the potential for faster project completion because less time is required on-site. Because of the way engineered flooring is constructed, it can be more stable in environments with varying changes in temperature and humidity. Recoating the finish can renew its luster; however, some engineered floors provide limited or no opportunities for sanding out dings or scratches. Color options may also be limited, providing less versatility to complement a wide range of décors.

A second type of hardwood flooring is site-finished flooring. This refers to the actual installation of unfinished hardwood on the job site, which is subsequently sanded and finished. Engineered floors can also be produced in this manner. (Site-finished flooring is the subject of the remainder of this learning unit.)

Site-finished flooring offers numerous advantages. After installation, the floor is sanded in place to level and smooth it before the application of a protective coating. Installed and sanded correctly, site-finished flooring is smooth and uniform, with no board-to-board bevels.

Site-finished flooring provides greater opportunities for a unique, custom flooring design. A wider variety of sheen, color and stain options can be used, or flooring can be stained to match existing trim and furnishings. In the long term, site-finished flooring lowers the lifetime cost of the floor. However, finishing hardwood flooring on-site extends the duration of the project, and can be extremely dusty and toxic if the wrong system is used.

WOOD SPECIESA variety of woods can be chosen for site-finished flooring:

CORK This is a softer material that originates from the bark of trees and can be harvested without harming them at all. It provides a softer cushion and thus has the potential to be more beneficial for anyone with feet, leg, back or joint issues. Cork is not only beautiful and sustainable, but it can also be finished and maintained like traditional hardwood floors.

BAMBOO Although actually a tree-like grass, bamboo has gained popularity as a wood flooring option because of its environmental attributes. It is a rapidly renewable material that grows faster than any of the hard, woody plants. When treated properly, bamboo forms a very hard surface that is both lightweight and exceptionally durable.

OAK This is the most common choice for hardwood flooring (approximately 70 percent of all hardwood floors are made of either Red or White Oak). Red Oak displays a pale, reddish brown character with darker sapwood and has an open and slightly coarser grain. It is used widely in furniture manufacturing because of its porosity. White Oak has a less pronounced grain and is light brown in color with paler sapwood. It is used extensively in the manufacturing of whiskey and wine barrels because of its closed cellular structure.

MAPLE This species is rated as one of the hardest domestically grown products available, as is evident by its extensive use in bowling alleys and basketball courts. Maple offers a closed grained wood with uniform texture, though individual boards may exhibit a highly decorative grain pattern. It also has very good acoustical properties.

HEART PINE In the pine genus, 100 percent Heart Pine has the highest level of hardness and durability, but it takes at least 200 years to achieve. Today, true "old growth" logs are being recovered and reclaimed from the bottom of river beds, yielding floors that are both timeless and beautiful in appearance. This further illustrates the sustainable nature of a product that is renewable and recyclable.

EXOTIC WOODS These products originate in many countries, and offer a diverse range of grain texture and hardness ratings, yet they have varying levels of extractives associated with them that can pose challenges when coating. Common exotic woods used for flooring include Brazilian Cherry, Tigerwood, Australian Cypress, Tiete Rosewood, Santos Mahogany, Brazilian Chestnut, Hickory, Brazilian Walnut (Ipe), Teak, Brazilian Oak, and Brazilian Maple.

STYLESThree primary style options are offered for site-finished flooring. Strip flooring features thin, long strips of wood, while plank flooring offers the aesthetic of wider widths of wood. Parquet floors have a completely different visual; they are more decorative and often made up of geometrical patterns composed of individual wood slats adhered or splined together.

GRADENational Oak Flooring Manufacturers Association (NOFMA) certification by the National Wood Flooring Association (NWFA) provides the assurance that the wood flooring being purchased meets or exceeds standards for grade, configuration, moisture content, and average board length. Mill inspectors trained by NWFA conduct mandatory quality control inspections twice a year to ensure that manufacturing and grading standards are being met.

NOFMA divides unfinished strip oak flooring into four grades:

  • Clear: minimum character marks and discoloration for a more uniform appearance
  • Select: few knots or streaks, with some color variations inherent in natural wood
  • No. 1 Common: more colorations than with Select, with small knots and varying degrees of mineral streaks
  • No. 2 Common: large knots and mineral streaks as well as vast color variations

THE SANDING AND FINISHING PROCESSSANDINGUnfinished wood floors should always be sanded to a smooth surface, according to accepted NWFA methods, which recommend at least two or three "cuts" or sanding operations. The initial cut should be performed with the least coarse-grade abrasive needed to get the flooring flat. Each subsequent cut should be completed with a finer grit of abrasive to remove the scratch marks left by the previous cut. When selecting grits, never skip more than one grit of abrasive or the cut will not effectively remove the scratches created by previous one, resulting in a rough surface and uneven appearance.

Dust Toxicity Chart for Selected Woods

Wood Type


I = irritant
S = sensitizer
C = cancer causing
P = hyper sensitivity pneumonia
DT = direct toxin

Potency Level

Bald Cypress




S, C









I, S









S, P



S, P



S, C




Very High


I, S





Pau Ferro







S, P, C



I, S

Very High







Walnut, Black







S, P





Sanding creates high levels of airborne wood dust, which is a known toxin and carcinogen (see the Dust Toxicity chart). While the level of toxicity varies according to the wood species, precautionary measures must be taken to prevent infiltration and permeation of dust into vents and air conditioning units. Traditionally, these steps include sealing off the work area, doorways and HVAC vents with plastic, as well as using a fan to exhaust dust from the work area. In addition, standard sanding machines have dust collection bags that collect large dust particles and filter the air that passes through (but they allow smaller particles to escape). These bags, however, must be emptied often to keep the air flowing through the system effectively.

If these precautions are ignored, the potential for poor indoor air quality is high as dust is circulated throughout the space. The result is a dangerous health hazard to the occupants, an occupational threat to those performing the work, and a huge challenge for the contractor charged with cleaning it up. Additionally, fine airborne dust particles will inevitably settle on the floor, causing a less-than-desirable "textured" final finish.Today, "dustless sanding" is becoming increasingly prevalent to help reduce health hazards and provide for a more unpolluted job site that doesn't require extra cleanup. Dust containment systems evacuate the airborne dust generated from the entire sanding process. These systems eliminate the need to hang plastic and cover openings, which results in a more efficient and faster work process and a higher quality of work. It also increases customer satisfaction because occupants are able to enjoy their spaces again that much quicker.

Dust containment systems also aid in meeting standards set by the Occupational Safety & Health Administration (OSHA) regulations for airborne dust particles. OSHA regulations limit dust particles to 1 mg/m3. Traditional sanding methods can generate dust particles exceeding 22.8 mg/m3.

STAININGOnce the sanding is complete, the wood can be stained to lighten or darken the floor; or it can be stenciled to create artistic expressions and faux appearances. Customers can choose from standard or custom stains to enhance the décor. However, while quick-dry stains are available, the staining process will add time to the project.

SEALINGEven if the floor is not being stained, it still needs to be sealed. A top quality seal coat prevents the wood from reacting with wood oils, resins, extractives and minerals. A quality seal also adds durability and creates an optimum foundation for the final finish that, with proper maintenance, will help the wood floor last for decades. An inferior seal, on the other hand, will require more frequent re-sanding and refinishing of the wood floor. A quality seal also minimizes side-bonding.

FINISHINGThe finish coat is the top wear-layer that adds the final level of durability and beauty to the wood floor. It protects the floor from wear, dirt and moisture, and provides chemical and scratch resistance. Two coats of finish are recommended for residential applications, and three coats for high-traffic commercial spaces. A number of choices are available for hardwood floor finishing; some are even formulated to meet the highest ADA standards for slip resistance. Sheen levels can also range from 5 to 90 degrees gloss to accommodate a wide range of design preferences.

Solvent-based (Class 1) finishes contain toxic solvents as the polyurethane carrier. These finishes have high levels of Volatile Organic Compounds (VOCs)—presenting severe problems for people with chemical sensitivities. These toxic fumes require the job site to be vacated during application. Their extremely low flashpoints have the corresponding danger of spontaneous combustion.

Oil is the polyurethane carrier for oil-based (Class 2) finishes. These finishes also typically have high VOCs and nauseas fumes that can be problematic to individuals with chemical sensitivities. These are non-flammable, but are combustible.

Waterborne (Class 3) finishes have water as the polyurethane carrier. The benefits of these finishes are lower VOCs, which means no harmful fumes and no need to vacate the job site. Waterborne finishes are also recommended for people with chemical sensitivities. Top quality high-performance waterborne finishes offer greater durability and beauty than solvent-based finishes because of their technologically advanced manufacturing process and non-yellowing characteristics. Also, the faster drying (two to three hours per coat) and cure times (90 percent in 72 hours) of a quality waterborne system are especially important for commercial and retail environments (see the Oil-Based vs. Waterborne Finishing Products chart).


Oil-Based vs. Waterborne Finishing Products

(based on 800 to 1,000 square feet)



Work Time

More contractor time on job = extra days at job site

Less contractor time on job = fewer days on job site


Amber color that will darken over time

Clear to amber color that will not change color over time

Dry Time

8 to 12 hours per coat

2 to 3 hours per coat

Cure Time

24 hours—40%

72 hours—50%

2 weeks—100%

24 hours—75%

72 hours—90%

1 week—100%

Days on the Job

Minimum 3 days

2 days

Proper care of hardwood floors is the most neglected specification aspect of hardwood flooring. Yet correct maintenance is critical to extend the floor's life and protect the customer's investment, thus avoiding costly and time-consuming refinishing.

Improper care of wood flooring includes the use of too much water, all-purpose cleaners or harsh chemicals, which can damage the wood and dull the finish. Also, dust mop treatments, oil soaps, silicone and acrylics can leave a residue and adversely affect the adhesion of a finish coat in the future.

For regular maintenance, vacuum or sweep regularly. Protective felt pads should be used on furniture legs and feet. Spills, sand and grit should be removed promptly. In addition, walk-off mats and area rugs are a good idea at exterior doors, stair landings and high-traffic areas (such as the cash register in a retail store). It's also wise to maintain a consistent humidity level in the space to keep the wood from swelling (which produces cupping, or shrinking, resulting in unsightly gaps between the boards). Humidity should be kept within a five- to 10-point range.

Choose a non-toxic, low VOC waterborne hardwood floor cleaner formula for indoor air quality, health and environmental benefits. For small areas, use a microfiber or terry cloth mop. For larger areas (such as commercial applications and sports floors), a commercial mop, buffer or autoscrubber can be used with a hardwood floor cleaner to remove dirt, stains and dried spills.

Recoating adds to the life of a wood floor; the frequency needed depends on the amount of monthly/annual pedestrian traffic and the level of daily and periodic maintenance. Recoat before the floor's finish is completely worn down. Recoating involves deep cleaning and abrading (also called screening) the old finish, removing dirt and surface scratches, and applying one or two coats of waterborne polyurethane finish. If the correct cleaner—one that does not leave any residue—has been used, then the new finish coat should adhere properly, saving the time and cost of having to completely sand off the existing finish. Recoat adhesion solutions can be used for conditioning the existing finish to optimize adhesion of the new coat of finish.

If the damage to the floor is severe and has penetrated the wood, sanding and refinishing will be required.


Case Study: Flatiron Crossing

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FlatIron Crossing, a retail mall in Broomfield, CO, attracts nearly 15 million visitors each year. For maintenance of its hardwood floors, the janitorial staff applied an acrylic-based maintenance coating intended for vinyl composition tile flooring.

Not only did this coating not wear well (low durability and scratch resistance), it actually acted as a contaminant for the hardwood floors by holding in the dirt. The result was a floor that had to be chemically stripped to clean it, which in turn added too much moisture to the wood and damaged floor boards.

FlatIron Crossing replaced the wood in two pedestrian bridges, while the remaining hardwood floors suffered severe cupping. This required a complete re-sand and refinish of 15,000 square feet, at a cost of $34,000 (after which, a waterborne polyurethane finish was used).

Today, the janitorial staff maintains the floor with daily dry dust mopping and cleaning with an autoscrubber twice weekly using a waterborne hardwood floor cleaner designed specifically for polyurethane finished hardwood floors. The mall also follows an established 12- to 18-month recoating schedule with a recoat adhesion system and waterborne polyurethane finish.

"Hardwood floors used to be our most expensive floor covering to maintain, now it is our least expensive," notes Randy Berman, assistant property manager for FlatIron. "With the right hardwood floor care system, we've cut our labor costs for maintaining our hardwood floors by 75 percent—a $60,000-a-year savings. And the floors look great!"

When choosing a sanding and finishing process, it is important to consider a number of variables. At the top of the list is the impact of the process on indoor air quality (IAQ).

The U.S. Environmental Protection Agency (EPA), the American Lung Association, the World Health Organization, and other public health and environmental organizations view indoor air pollution as one of the greatest risks to human health, in large part because people spend 90 percent of their time indoors.

Immediate effects of poor IAQ include irritation of the eyes, nose and throat, headaches, dizziness, allergies, and fatigue. Indoor air pollutants may also trigger symptoms of some diseases, including asthma, reproductive and developmental problems, and cancer. Additionally, interior product emissions can also result in sick building syndrome. The traditional sanding and finish process, which uses solvent-based finishing products and lacks dust containment, creates an environment of hazardous airborne wood dust and harmful fumes in a home or business. In fact, the wood dust particle count with traditional sanding equipment is more than 20 times the OSHA limit, resulting in an unnecessary threat to workers' health and an inconvenient mess for their customers.

To help evaluate IAQ effects of various products, the GREENGUARD Environmental Institute (GEI), an independent, nonprofit organization, establishes standards and testing for indoor products, including hardwood floor finishes and cleaning agents. For the healthiest alternatives, look for products that are certified low-emitting by GEI. It is also important to note that the LEED® Green Building Rating System recognizes GREENGUARD certification for IAQ standards.

Another critical consideration is the new regulation by the EPA regarding lead certification. The rule sets guidelines requiring contractors who perform renovation and repair work in facilities built before 1978 to comply with several mandates, including certification and following specific work practices to prevent lead contamination. Flooring contractors could be affected if more than 6 square feet of lead-painted areas are disturbed. In most situations, this would include baseboards, in which case, 32 linear feet of 2¼-inch baseboard would make the law enforceable. Lead in dust is the most common way people are exposed to lead. Projects (such as sanding) that disturb lead-based paint can create dust and endanger workers and occupants. Part of lead safety when renovating hardwood floors requires power tools that have high efficiency particulate air (HEPA) filter attachments to contain the dust.

New air quality regulations for VOC levels went into effect around the United States beginning in January 2005. National VOC regulations restrict VOC limits to 450 g/L. In many states, however, the VOC limit for finishes has dropped to 350 g/L. Some agencies have even proposed and enacted a 275 VOC g/L limit for finishes. In states where new laws have been adopted, contractors can be fined up to $500 per gallon for use of noncompliant products such as oil-modified and moisture-cure polyurethanes with VOC levels above 350 g/L. Distributors can be fined up to $4,000 per offense and manufacturers can be fined up to $10,000 per offense for administrative requirements.


Dave Darche is director of continuing education at Bona US. He is an NWFA-certified inspector and a 30-year hardwood flooring industry veteran. He can be reached at