By Olde Wood
Oil-Based Polyurethane, Water-Based Polyurethane, and Natural Oil?! Huh?
Nearly as important to the character of a room as the wood you put into it, choosing the right finish option is the all-important final step in creating your envisioned hardwood flooring experience. Finishes roughly fall into three categories: Oil-Based Polyurethanes, Water-Based Polyurethanes, and Natural Oils. We’re going line them all up and see how they compare in terms of look and feel, application, durability, repairability, cost, and environmental impact.
LOOK and FEEL
Both oil and water-based polyurethane finishes serve as a protective layer that sits on top of the wood. This added top layer gives a noticeable sheen to the hardwood. The most distinguishing difference between the two is the amber tint of oil-based polyurethane compared to the almost perfect clearness of water-based polyurethane.
Oil-based polyurethane accents hardwood with a golden shade, and this warm tone darkens slowly with time. For some hardwoods, such as Oak, this tone is often sought and considered complimentary to the wood.
Those looking to preserve the natural colors of the wood, however, should use water-based polyurethane. Water-based polyurethane goes on clear and stays clear. This maintains the natural look of the hardwood, while still imparting the surface sheen of a polyurethane finish that amplifies its character. (It should be noted, though, that some water-based sealers are available with amber/golden color enhancers.)
Unlike the satin to glossy polyurethane finishes, natural oils do not dry on top of the floor, but rather penetrate into the wood and harden. This creates a low-sheen matte finish that allows the grain and texture of a hardwood floor to remain a part of its appearance. Natural oils have grown in popularity in recent years, as the demand for natural, “old world” flooring has risen. This finish option can be clear or used in combination with a stain in a variety of colors.
Depending on the brand, oil-based polyurethane can require from eight to twenty hours of dry-time per coat. Since two or three coats are required this means that selecting oil-based polyurethane as your finish option will put the project-area out of commission for two to three days. Oil-based polyurethane also emits a prominent chemical odor that dissipates with time, and tools must be cleaned with a solvent—such as mineral spirits or paint thinner.
On the positive side, because oil-based polyurethane dries so slowly it can be worked when wet. This “wet edge” allows for mistakes to be corrected and gives beginners significant wiggle room as they learn.
Water-based polyurethane dries extremely quickly. A coat of water-based will be dry to the touch in one hour and ready for the next coat in two. This fast drying allows very little room for error. Water-based poly loses its wet edge almost immediately, and correcting mistakes during the application is extremely difficult.
The rapid drying of water-based polyurethane does present the advantageous ability to apply all four required coats in a single day. Also, water-based polyurethane emits very little odor, and clean up of tools requires only water.
Comparable to waxing a car, natural oils present the most forgiving finish application process. The oils are absorbed into the wood as they are applied and the excess is then removed. The oil left behind hardens in the wood and the floor is then buffed. Spots may be touched up and mistakes gone over at any point without affecting the uniformity of the finish. This cosmetic forgiveness is difficult at best when using a polyurethane finish, and often impossible. Natural oils have little to no odor, and depending on the brand the application process should take one to two days.
Polyurethane finishes and natural oil finishes have very different strengths and weaknesses in regards to durability.
The durability strength of a polyurethane finish lies in its ability to act as a coat of armor for the hardwood below. Both oil and water-based polyurethanes do an excellent job of protecting the hardwood itself from damage. They do, however, show scratches and wear marks more and more over time as the finish layer becomes etched.
Natural oils are durable in the opposite way. A natural oil finished floor will show almost no scratches or wear marks because there is not a glossy layer on top to be etched. The drawback is that the wood itself is more vulnerable to impact marks without the protective shell of polyurethane.
A good way of thinking of it is that polyurethane finishes are very durable against dents and dings, but will show scratches and wear. Natural oils are just the opposite—very resistant to traffic but more vulnerable to impact.
RENEWING and REPAIRING
There are two primary options for renewing and repairing the finish of a hardwood floor. The first, and usually preferred option is re-coating. When a hardwood floor is re-coated, the floor is buffed and a new layer of finish is simply applied over the existing, worn layer. This approach to renewing a floor can be done with either polyurethane finishes or natural oil, but generally gives better results with natural oil finishes.
The second renewing option is completely refinishing the floor. Floors with oil and water-based polyurethane finishes sometimes require a full sanding and re-application of finish to repair damage and wear. Because this sanding erodes some of the hardwood wear layer, there is a limited number of times this can be done. A complete refinish is usually only done to polyurethane finished floors.
There is another variable that comes into play when determining which method of finish renewal is to be used: the surface texture of the hardwood.
Many Olde Wood reclaimed floors, have original, rustic textures that are not sanded or given a flat finish. Floors such as Hit Skip Oak and Historic Plank cannot be refinished because the required sanding would remove their authentic textures. Unless removing this texture is desired, textured floors must always be re-coated.
In such cases special bonding agents may have to be applied for the new finish coat to properly set on the textured surface.
The primary environmental concern surrounding hardwood finishes is their release of VOCs (Volatile Organic Compounds) into the air. In addition to often being greenhouse gases, VOCs can cause long-term health effects if inhaled in excess or for extended periods of time. Oil and water-based polyurethane finishes both emit VOCs into the air during application and continue to do so for some time afterwards. Oil-based polyurethane releases significantly more VOCs than water-based. It should be noted however, that most of the leading finish manufacturers have reduced the VOC amount in their products to a safe, and nearly negligible level.
While there are now low-VOC polyurethanes available, natural oils run away with the title of Most Environmentally Friendly Finish. All natural oils release little to no VOCs, and many brands, such as Rubio Monocoat, are totally VOC free.
Prices will vary with brand and installer, but Oil-based polyurethane is generally the least expensive finish option. Water-based polyurethane usually costs three times as much and can require up to two more coats. Natural-oils are the most expensive per square foot, costing up to five times as much as oil-based polyurethane, but most brands require only one or two coats.
Choosing the right finish option is a task that requires a little homework, but is always rewarding. Hopefully this post provided some insights that help clarify the right selection for your project.