The finish you choose for your hardwood flooring has two dynamic implications. The first is aesthetic. What will the finish look like on your flooring? Or more pointedly, what effect will it have on the natural beauty of the wood, its radiance, its grain pattern, its predominant color tones, and its variations in color and brightness? The second is about durability; that is, which finish will best help protect your floor from scratches, gouges, and dents.
Of course, there’s no one simple answer. Life is rarely that easy. Each wood species used for flooring has its own unique characteristics that may compel the choice of one type of finish over another. Additionally, your own unique tastes play into the choice as well. But a little information can go a long way toward helping make this a less complicated decision.
Flooring finishes fall into two camps: surface finishes and penetrating finishes. As their names suggest, surface finishes remain on the surface of the wood to establish a protective shell, whereas penetrating finishes permeate the pores of the wood before hardening and creating a durable, long-lasting integral defense. Surface finishes include polyurethane, acid-cured (Swedish finish), shellacs, and aluminum oxide. Penetrating finishes include natural oils such as linseed, tung, and Danish oils, as well as hard wax oil finishes.
With a surface finish on your floor, you are walking on and making contact with the finish rather than the wood. And as wear occurs on the floor, it is the finish rather than the wood that is being worn away. Surface finishes function by combining a resin and a solvent. The solvents, which allow the resins to be fluid, then evaporate once the finish is applied, leaving the resin to establish a film coating on the wood.
Surface finishes have their pros and cons. On the positive side, once applied, they set up relatively quickly, making the waiting period for moving in and using the flooring relatively short. There are a variety of sheen options, from high gloss to subtler effects closer to a satin. Over time, the once clear resins can begin to yellow, darkening and deepening the wood’s appearance. This might be considered a positive or a negative, depending on the species. The hard surfaces these finishes form are easier to clean than most penetrating finishes but can show scratches, and are harder to repair, most likely prompting a complete refinishing as opposed to a touch up.
The most popular surface finishes are oil-based and water-based polyurethanes. Water-based polyurethane, which can be applied relatively easily, dries quickly (12 hours), has low odor and low volatile organic compound (VOC) emission, and maintains a clear, smooth, shiny finish. Oil-based polyurethanes require fewer coats when applied but take a little longer to dry and cure (48 hours), and emit strong fumes and VOCs, requiring a ventilator. The odors will linger for several days. Oil-based poly has an amber tone that will immediately darken the wood and will deepen over time. Water-based poly is harder than oil-based, which means that it is more susceptible to surface abrasions, whereas oil-based is more prone to denting.
From an aesthetic standpoint, water-based poly will leave your floor’s color unchanged. This is often preferable for woods that are gray or other light tones. Oil-based poly will push woods with a hint of yellow deeper toward gold. Darker wood tones such as red oak or cherry, however, can be enriched by the amber hue and oily sheen.
Shellac is created from a resin secreted by the lac beetle, native to India and Southeast Asia. It has no odor and is quick drying—so quick that application takes practice to avoid lap lines. It has excellent adhesion characteristics that make it a good choice when working with oily woods, such as many exotic tropical species, or pitchy woods, like pine. Shellac does not have the durability of urethane-type finishes, but it is easy to touch up damaged areas.
Acid-cured finish, also known as Swedish finish, is a quick-drying, slow-curing, extremely durable option often applied to exotic wood floors or those with elaborate patterns, such as parquet flooring. In addition to its durability, it is highly transparent, and has excellent elasticity. On the downside, its very high VOC content, which includes formaldehyde, along with its difficult application process, suggests hiring a professional, which adds to its already high cost.
Aluminum oxide is a naturally occurring element, typically found in a crystal form, and is used as an abrasive for sandpaper. When ground into a white powder, it can be used as a fortifier for urethane, providing hardness and abrasion-resistant qualities that give it the highest level of protection from wear and tear. Aluminum oxide finish has a lifespan of up to 25 years, which is especially beneficial for engineered hardwood floors due their thinner wear layer which limits the number of times they can be refinished. Aluminum oxide is only available on new, pre-finished planks due to the specialized application and drying equipment utilized in the process.
Aluminum oxide urethane dries clear, with minimal changes in color, and does not enhance grain patterns as much as polyurethane. It is available in several levels of glossiness. And though scratching is rare, when it does happen, they show up with a whitish powdery look and are harder to repair because of the hardness of the material.
When you touch a floor to which a penetrating finish has been applied, you are in contact with the wood rather than the finish. This, along with most oil’s natural origins (linseed from flax seeds, tung from nuts, etc.), provides purists with a robust rationale for penetrating oil finishes. Additionally, they tend to enhance the natural colors and qualities of the wood, and their low sheen leaves the floor looking less adulterated. They are also generally easier to apply than are surface finishes.
On the downside, after application, these finishes are slow to set up, and don’t provide resistance to solvent damage or staining. However, unlike most surface finishes, scratches can be repaired by recoating the damaged area rather than requiring an all-out refinishing. Penetrating oils are more flexible than most surface finishes, moving with the wood as it expands and contracts. And stains can often be added to penetrating finishes to change the look and character of the wood as desired.
Penetrating Oil Sealer
Oil sealers have long been utilized for flooring. Oil has a more mellow, lower luster sheen than do poly finishes. Because the oil penetrates the wood, it can also deepen the color and highlight the grain of the wood, providing your floor a rich, beautiful finish.
Most penetrating oil sealers/finishers are combinations of highly modified natural oil, most often linseed or tung oil, with additives to improve hardness and drying. Though less durable than polyurethanes, oil sealers are easy to apply and repair. And they will not crack, craze, or peel, though they can water spot.
Hard Wax Oils
Hard wax oil finishes are a non-toxic, no-VOC option that permeates the wood and acts as a barrier against stains and moisture. Hard wax oil finished floors are more water resistant then polyurethane-finished floors because the cells of the wood are not closed off, allowed them to breathe. This porosity simultaneously acts to protect against drying out over time, preventing warping and weakening.
These finishes come in a range of colors, from clear to dark amber, and create a warm, natural matte appearance. The actual finishing process is quick and easy. This means that the repair process is easy as well. Hard wax oil finished floors can be spot repaired with just a light sanding of the affected area followed by a topical coat of oil. Floors finished with hard wax oil do require a periodic coat of maintenance oil, though the process is not difficult and can be accomplished by the homeowner.