All You Need to Know About Wood Flooring Finishes

There have never been more finish options in the wood flooring market than there is today, and never more confusion—for both consumers and wood flooring contractors—about which one to choose. Old-school finishes, like wax, are experiencing a renaissance of sorts, old standbys like oil-modified polyurethane are evolving due to environmental regulations, and new varieties of finishes are moving into the market, often from our European counterparts. How to make sense of this changing landscape? Here is a summary of the basic finish types found in the modern wood flooring world. Keep in mind that the following summaries are generalizations for each type; always get the specifications and follow the directions for your specific product.

Wax

Wood floor wax is made from carnauba wax, which comes from the leaves of the Copernicia prunifera palm tree, native to northeastern Brazil. The leaves are collected, dried and beaten to loosen the wax, and then the wax is refined. For application as floor finish, mineral spirits are added to the wax.

Wax has been used as a wood floor finish for hundreds of years, and it was the predominant finish for wood floors until the prevalence of polyurethane-type finishes in the 1950s. With the trend of low sheen finishes in recent years, wax has experienced a resurgence of popularity in some areas, particularly with specialty wood flooring contractors working with reclaimed/distressed flooring and historic renovations.

Paste wax is buffed into wood flooring with a rag or burlap sack, while liquid wax is spread with a lambswool applicator. With either method, the wax hardens and is then buffed with, typically, steel wool or a white pad.

Advantages:

• Does not give the appearance of having a coating on top of the floor.

• Wax floors can be walked on only a few hours after application.

• Sheen can be determined by the material chosen to polish the wax coats.

• If desired, consumers can maintain the floor themselves. Problem areas and traffic patterns can be repaired easily by adding more wax and buffing; the entire floor does not have to be recoated.

Disadvantages:

• Too much wax on the floor attracts dirt and scuffs easily.

• Durability does not compare with urethane-type finishes.

• Wax is slippery and therefore not recommended in a commercial setting or on stairs.

• Because water turns the wax white, it is not typically used in kitchens or bathrooms.

• Its tendency to age with a yellowish patina can make it a poor choice for light-colored floors, such as a floor with a gray color or a natural maple floor.

• Requires regular maintenance/re-waxing.

• Recoating with other coatings may require completely sanding the floor.

FACT: A wax floor that is extremely slippery is an indication that there is too much wax on the floor. Excess wax is usually removed with a buffer, steel wool and mineral spirits (note that mineral spirits is no longer legal to use in all areas). Shellac

Shellac has bragging rights as the wood floor finish with the most unusual origin: It is created from a resin secreted by the lac beetle, native to India and Southeast Asia. The resin is scraped off tree branches, heated and filtered, then dried into flat sheets that are broken into flakes. Shellac is dissolved into ethyl alcohol for application. The liquid form is described by the “pound cut,” which is how many pounds are dissolved into one gallon of alcohol. Shellac naturally contains a small percentage of wax, but liquid dewaxed shellac—often referred to as “universal sealer”—is typically used on wood floors.

Shellac has been used as a coating for thousands of years. In the wood flooring industry, it was, and remains, most often used as a sealer coat.

Shellac by itself is so safe that it is still used as a coating for candy, pills, and many other items. When mixed as a wood floor finish with its alcohol solvent, however, increases the VOC levels, which is not recommended for consumption. It has its own VOC category, so it has higher VOC limits than most wood floor finishes.

For flooring, a 3-pound cut of liquid dewaxed shellac is typically used. The manufacturer’s directions should be followed for application; typically, contractors use a lambswool applicator or a brush. Application takes practice due to its quick dry time (some contractors find that thinning the shellac down to a 2-pound cut can help avoid lap marks but thinning the shellac may cause it to exceed its VOC limit). A steel wool pad or maroon pad is used to abrade between coats. Typically, shellac needs at least a two-hour dry time.

Advantages:

• Natural sustainable supply.

• No odor.

• Relatively quick drying (usually two hours or less).

• Has great adhesion characteristics, so some contractors use dewaxed shellac as their go-to sealer when they are concerned about potential adhesion problems (often during recoats) or when working with oily woods, such as many exotics, or pitchy woods, like pine.

• Because it is available in an amber color, some contractors use it to get color on the floor underneath a waterborne coating. Note, however, that this is not endorsed by most waterborne finish manufacturers.

• Easy to touch up (buffing with steel wool or a maroon pad and applying more shellac is a simple repair).

Disadvantages:

• Being alcohol-based, shellac is extremely flammable. All pilot lights and other ignition sources must be turned off, any equipment with motors that are not explosion-proof should be kept off, and light switches should not be turned on and off, or the vapors can easily ignite.

• Although it does not smell, some contractors say it creates a burning sensation in their eyes.

• Requires practice to apply without lap lines, especially when using amber shellac.

• Durability does not compare with urethane-type finishes.

• Most finish manufacturers will not endorse its use with their finish systems.

• Due to its VOC levels, it may not be available in areas with the strictest VOC limits or may be available only in quarts.

FACT: Liquid shellac has a limited shelf life—about six months. If you use a batch that is too old, it will not harden.

OMU

Although we refer to it in our industry as “oil-modified polyurethane,” (or OMU, or poly, or many other names), technically it is polyurethane-modified oil (usually linseed oil). It is polyurethane with an oil base in a solvent as the carrier. The solvent is typically mineral spirits, although some new poly products have water instead. OMU was developed in the 1940s and came into use for wood floors during the ’50s and ’60s. While it is still the most common wood floor finish, although more restrictive VOC levels have diminished its popularity in certain markets.

OMU products have been among those most affected by the patchwork of VOC laws in effect in the United States, leading to a variety of products on the market at different VOC levels depending on what is required by law, with quarts still available in some markets at higher VOCs (Volatile Organic Compounds).

A lambswool applicator or a brush were traditionally used for OMU, but some contractors find rollers or T-bars work better, particularly for VOC-compliant products.

Advantages:

• An extremely forgiving finish that is slow-drying and easy to apply without applicator marks.

• Low-cost.

• Many people find the amber color desirable, particularly on species such as walnut and many exotics.

• Provides a substantial build on the floor that gives a rich depth to the wood.

• High build per coat compared with waterborne products.

Disadvantages:

• Generally aimed at the residential market.

• Some people find the odor unpleasant, although some newer VOC-compliant products have less odor than earlier generations.

• Newer VOC-compliant formulations have more solids; they can be slower to dry than original formulations, and they can be difficult to apply at the (thin) mil thickness required to get the correct spread rate.

FACT: Lead was used as a drying agent in oil-modified poly and stain until its use was banned in coatings due to health concerns in 1978. Because lead helped a coating dry from the bottom up, before its ban, common problems in today’s market like finish poly beads and stain bleed back were unheard of. Today, contractors disturbing more than 6 square feet (about half the area of a bathtub) of a coated surface in any pre-1978 home or child-occupied facility must be certified under the EPA’s accredited training. Lacquer

Lacquer is a nitrocellulose dissolved in lacquer thinner with a plasticizer or similar material. Some types of lacquer have been used for thousands of years, and the material nitrocellulose was first created in the 1800s. The lacquer we think of as a wood floor sealer has been used since the first half of the 1900s; back then it was usually a sealer under wax.

Lacquer was still relatively common in the wood flooring industry as recently as a decade ago but fell out of favor due to its inherent dangers and resulting deaths. Today it is more commonly used in the furniture finishing industry. There are small pockets of contractors in areas such as Toronto, Chicago, Detroit, and some parts of the East Coast, however, who use still use lacquer as a sealer coat. Like some previously mention finishes, it is often applied with a metal trowel.

Advantages:

• Extremely fast-drying—you can usually coat over it in 15 minutes.

• Because its re-dissolves itself, a problem in one coat can be eliminated with the next coat.

Disadvantages:

• Lacquer has an extremely low flash point (the temperature at which it will ignite when exposed to a source of ignition, like a pilot light), and is even more flammable than shellac, so it must be used with great caution (all the same precautions about pilot lights, etc., apply to lacquer). When you hear a news story about a wood flooring job site blowing up while the workers were on the job, most often they were using lacquer finish. A brittle finish with poor durability.

• Not compatible with some finishes and not endorsed by wood floor finish manufacturers for use with their systems.

• Most insurance companies will not ensure companies that use lacquer finish.

Waterborne

There are many varieties of waterborne coatings in the wood flooring market; depending on the product they may contain acrylic, polyurethane, or a combination of both. One- and two-component versions are available. Among the most recent waterborne coatings are those that cure with UV light.

The first waterborne finishes hit the wood flooring market in Europe in 1979 and reached the United States in the early ’80s. Waterborne is a close second to oil-modified polyurethane in popularity and still increasing in popularity. Particularly popular in areas with stricter VOC regulations. By their nature, waterborne coatings have lower VOC levels than most other wood floor finishes. Some manufacturers have developed even-lower-VOC products to appeal to consumers with environmental or health concerns.

T-bars are the longtime applicator of choice for waterborne finishes and are still the most popular, but today many waterborne finishes can also be rolled.

Advantages:

• Some people prefer the clear color that many waterborne finishes offer, particularly for species such as maple and hickory, as well as other light-colored floors such as those with light gray or white stains.

• Do not discolor or yellow over time.

• Some manufacturers offer them in both clear and amber appearances.

• Relatively fast dry times, allowing more than a single coat in one day.

• Ability to “hot-coat”—apply another coat of finish without abrading the previous coat (within a specific period after the previous coat).

• Less odor than many traditional finishes.

• Low VOCs.

• Non-flammable.

• Good chemical/stain resistance.

• Products available for residential, commercial and sports applications.

Disadvantages:

• Some people do not like the clear color, particularly for some species. Some manufacturers have developed products for those cases with an amber appearance.

• Takes practice to apply without applicator marks, particularly in areas with extremely low relative humidity.

• Higher cost than solvent-borne coatings.

• The aziridine and isocyanate ingredients in some waterborne finishes should be handled with care—gloves should always be used when handling them. With repeated exposure, some contractors become sensitized to the products, leading to reactions even without direct contact.

• Traditionally has less odor than oil-modified poly, although some people find its odor to also be objectionable. As VOC levels decrease, so does the odor.

TIP: Never watch a waterborne finish while it is drying. If you notice a blemish in the waterborne finish you are applying, do not try to fix it while the finish is wet. During the drying process, the finish may appear to have many imperfections. As the finish pulls down, the imperfections disappear. If repairs are necessary, do them after the coating has dried.

Moisture-Cure Urethane

This is a true urethane finish with strong solvents. It draws water vapor from the air to cure. Moisture-cure came to the wood flooring market from the bowling lane market in the early ’70s. Due to environmental and health concerns, it is not commonly used in today’s wood flooring market and is more prevalent for industrial applications. For this finish, the market is concentrated in New England, the Carolinas and Canada. There is a choice of applicators for this product, such as lambswool applicator, roller, or brush.

Advantages:

• Extremely good characteristics for wear- and chemical-resistance, meaning it was often chosen for high-wear situations such as restaurants, dance floors and roller rinks.

Disadvantages:

• The strong solvents in moisture-cure urethane are known to have neurological effects with repeated exposure, so contractors must use a full-face respirator or a fresh-air-supply mask.

• Full-body suits are recommended. Any pets in the house, including fish in aquariums, must be removed during coating.

• Because it draws moisture from the air to cure, it is difficult to get it to dry and cure in dry climates. In some very humid climates, it may skin over too fast and trap solvents below, causing foam and curing problems, so it is not recommended when the relative humidity is over 70 percent.

• Because flattening agents used in finish contain moisture, in our industry moisture-cure finish is generally available only in a high-gloss sheen.

• Due to its highly active solvents, it can only be used over raw wood or itself. Screening between coats is necessary.

• Among the most challenging finishes to apply, and even more so with newer VOC-compliant formulations.

FACT: In very high-humidity situations, moisture-cure finish can begin to dry as the brush is being pulled out of the finish can. Conversion Varnish Also known as Swedish finish or acid-cure, conversion varnish is available as a one- or two-component finish. It typically has alcohol as a solvent and cures because of acid catalyzation. The finish was developed in Sweden in the early 1950s and introduced to the U.S. market later that decade. Conversion varnishes have strong pockets of contractors in the Pacific Northwest, Mountain, Midwest, Northeast regions, and Western Canada. Depending on the product and the user, a roller, T-bar, or lambswool applicator can be used.

Advantages:

• Extremely durable and chemical-resistant.

• Quick drying, allowing multiple coats to be applied in one day.

• Depth of color comparable to an oil-modified poly.

• Smaller molecules dive into the wood, protecting wood cells.

• Excellent grain clarity, depth, and color.

• Easy repairs due to the coating’s ability to wet back into itself.

Disadvantages:

• Extremely flammable, so all pilot lights and other ignition sources must be turned off during use.

• Strong odor—after application, the job site must be ventilated with as many air exchanges as appropriate. Closing the home can delay the curing process and prolong the smell in the home. All pets, including fish, must be removed from the home.

• Full-face respirators should be used during application. Because the finish releases a small amount of formaldehyde during curing, respirators should have organic vapor cartridges suitable for formaldehyde release. Many contractors choose to use full-face body suits to protect their skin.

• Any direct drafts over the floor during application must be avoided. Indirect ventilation is necessary.

FACT: Whether a finish is considered flammable, or combustible depends on its flash point, the lowest temperature at which its vapors ignite in air when exposed to an ignition source. If a liquid has a flash point below 100 degrees Fahrenheit (37 degrees Celsius), it is considered “flammable.” If it is between 100–140 degrees, it is combustible. (Products above 140 degrees require no designation.) Natural Oil Finish

A wide spectrum of finishes are lumped into this catch-all category because all use a type of natural oil as the base. These finishes can be broken down into further categories, including penetrating oils, which absorb into the wood and leave no surface films; hard wax oils, which contain wax to create some build on the floor; and hybrid oils, which are oils (such as tung oil) combined with urethanes that form a film.

The time spent on the market varies widely depending on the product. Tung oils have been on the market for more than 100 years; while hard wax oils were in use in Europe before being introduced to the U.S. market in the last 10 years.

The VOC levels of natural oil finishes vary widely, from no VOCs or very low levels for products such as hard wax oils with a vegetable base, to a higher VOC level for hybrid oils such as tung oil with a high percentage of mineral spirits as their solvent.

The directions for these finishes are specific to each product. Some are spread with a steel trowel, while others are buffed in. Some require only one coat, while others need multiple coats.

Advantages:

• Easy to apply.

• Provide a natural, organic-looking floor without film build.

• Some products in this category offer a wide range of color options, including some that offer the ability to create multi-layered colors.

• Typically easy to do spot repairs (multi-layered colors are more difficult); high-traffic areas can usually be refreshed by adding more oil.

• Without a film build, the wood can adjust more readily to changes in relative humidity, helping reduce cupping and crowning.

• Due to low VOCs, some products appeal to customers with environmental and health concerns.

Disadvantages:

• Among the most expensive finishes.

• Require an excellent sanding job, as there is no finish build to help hide imperfections.

• Some products have a short pot life once mixed with the hardener, so must be mixed in batches at the job site and applied in small sections.

• Most require maintenance comparable to that of a wax floor, with periodic re-oiling.

• Poor chemical resistance.

TIP: Typical wood floor cleaners can damage natural oil finishes. A wood floor with one of these finishes should be maintained only with the specific product recommended by the manufacturer. Job-Site UV Cured

This is a specific waterborne finish that cures with a photo initiator instead of a catalyst. Waterborne finish is applied with the usual methods, but once the finish is dry enough to walk on, the machine is run over the floor, bringing the finish to its final cure instantly. Furniture, rugs, and traffic can be on the floor immediately afterwards. This method was introduced to the wood flooring market in about the last five years. It applies the same as other waterborne finishes, with the addition of the UV curing process.

Advantages:

• All the advantages of typical waterborne finish, plus:

• Customers can get back onto their floors immediately once the job is done.

• Most offer wear typical of a two-component waterborne finish, but manufacturers of some newer versions say their products have wear comparable to a moisture-cure finish.

Disadvantages:

• The finishes require purchase of a job-site UV light machine, which starts at $5,000 (and is often much more).

• The machine and finish must be paired precisely: Too little light will not cure the finish enough, making it soft; too much light will overcure the finish, making it blister.

• The contractor must take care with the machine to not burn the wood floor by leaving the machine running in one place too long.

• The contractor must remain on the job site to go over the floor with the UV machine once it is dry enough to walk on.

• The intensity of the UV light exposure is equivalent to 25 tanning beds, so contractors should wear eye protection, long sleeves, long pants, and high-SPF sunscreen when using the UV machine.