By Johannes Boonstra
With the increasing demand and desire for trendy colors in today’s interior décor, wood flooring professionals need to understand how to provide customers with looks that are often different from the natural color of the wood species used for the installation of the wood floor. Most of us have used and are familiar with traditional stains to alter the color of wood, and are reasonably comfortable with those processes, but perhaps are not always familiar with the actual makeup and limitations of a stain.
You may have heard of dyes, reactive stains, and the terminology “shading or glazing.” So, let’s take a closer look what we may use on a site-finished job when adding color to the wood floor is required.
A stain is basically simple in its makeup, the ingredients used for manufacturing a stain are: pigment, binder, solvent (aka carrier) and additives. The pigment used may be organic (earth pigments) or sometimes a synthetic manufactured pigment particle (like iron oxides or TIO2), generally pigments are fairly lightfast (some are less lightfast and may fade a bit). Depending on the pigment grind and color and/or pigment load, a stain color may be light or dark and may be transparent, semi-transparent, or semi-solid (more opaque or “muddy” in appearance). Pigment does not dissolve in the solvent but is suspended in the liquid, so it may settle due to its weight (may require periodic stirring during use).
The binder is a resin, whose sole purpose is to bind the pigments to the wood fibers/cellulose where the pigment particle has penetrated/is laying on/in the woods substrate, at the same time the small amount of binder/resin also seals the stained wood. Without the binder, the pigment would easily rub off or lift off with manual finish applications once dry. A typical wood floor stain is formulated to penetrate and meant to be only applied in one application, as with multiple applications there is simply not enough binder/resin to hold on to the pigment deposited on the substrate. The binder in oil-based stain may be linseed oil, an alkyd/urethane resin, or a combination of both.
Oil-based stains are available in higher VOC versions and low VOC versions. While the environmental benefits of a low VOC stain are obvious, the consequence with low VOC formulated oil-based stain is that typically less solvent/carrier is used in the formulation with a higher binder/resin load. This makes the product by its own nature (higher solid content) a bit more challenging to properly apply; meaning more physical work required to assure not too much product/resin is left on the stained substrate. Also, this results in extended drying time before a finish-coat may safely be applied. Generally, oil-based stains provide longer “open-time” and are the easiest with which to work. Linseed oil type stains generally give more open time and dry a bit slower than the alkyd/urethane type (“quick dry” versions).
Additives in oil-based stains would be, for example, the drying agent; they are often metallic salts and may be referred to sometimes as siccative (driers). This additive in the formulation accelerates the reaction of the binder with oxygen once it has been applied (after the solvents evaporate), so an oil-based stain is therefore called an oxidative drying product. Once applied, and the solvent has evaporated, it is important to provide good airflow/oxygen.
When the binder/resin of a stain is water soluble (latex/acrylic binder) by its own nature, a stain would be categorized as a waterborne stain.
Waterborne stains are much different to work with in comparison to oil-based stains due to the shorter open-time and overlapping effects which may create lap marks. Waterborne stains are also very low VOC and are becoming more prominent as VOC regulations continue to tighten up. Waterborne stains are less harmful to the environment and to the individual applying it. Waterborne stains do require learning new application methods, but offer many color, application, and health benefits otherwise very difficult to achieve.
Dyes are different compared to wood stain and are the oldest known coloring agents. Dyes are mentioned in the Bible, and written history proves that as far back as 2600 B.C., organic dyes were used in China. In the olden days, they were extracted from roots, nuts, fruits, bark, and insects yielding nice colors that were very transparent but exhibited very poor lightfastness. In the mid-1800s, a big breakthrough occurred by accident and a new “dye stuff” was discovered by experimenting with coal tar (with a poisonous coal tar byproduct called aniline), the dye stuff derived from this is also known as aniline dye. This product was more lightfast than organic dyes; this is when the development of new synthetic (non-organic) dyes started. Dyes were primarily used for dyeing fabrics, but later in the 1800s, woodworkers also started using them because of the tremendous transparency and better lightfastness compared to organic dyes.
Dyes are many times finer in particle size (at a molecular level, you may compare it as a needlepoint versus a football) compared to pigments, so that is a huge advantage if one wants to maintain the best possible clarity when coloring wood. Dyes completely dissolve in a solvent where pigments don’t.
In the mid-1900s, metal complex dyes were developed, which resulted in the benefit of a further increase of lightfastness, but, still all dyes fade more than pigments (we will address this later in this article).
Depending on the formulation, dyes may be soluble in oils, alcohol, or water. For dying wood flooring on a job site, we typically don’t use alcohol dye as it dries instantly, which is not very practical. So, we use mostly water-soluble dyes. Dyes are available in powder form or in a solution of alcohol, so both are soluble in water. Due to the strong coloring strength of dye, a small amount of powder/concentrate makes a large batch of dye.
Dye penetrates deep and bonds to the cellulose of wood, even the densest wood species will absorb dye. Its application is challenging if one has never used it before and typically a second application is applied to intensify and even out a color and to blend in lap marks from the first application. But, dye dissolves in the solvent it was mixed in (in our case water), so, therefore, it can also dissolve and migrate out of wood when exposed to water. This means we need to protect it before finishing it. Also, as mentioned before, we know that dyes are not very lightfast either, so we must protect the dye from light somehow. Remember that pigment in stain is more lightfast. This is the reason why a dyed floor needs to be completed with a good quality oil-based floor stain before applying a finishing product; an oil-based stain is selected for this purpose. (Note: the dry dyed wood tone is completely different from the finish coated dyed floor. Make samples to pin down the final color before applying to the job site).
Chemical Reactive Stains
Chemical reactive stains react with tannic acid present in wood species. Therefore they are most effective on wood species that contain a high amount of tannic acid. Examples of such species include: white oak, walnut, Brazilian cherry, black (American) cherry, and mahogany.
The most well-known reactive stain terminology here in the U.S. you may have heard of is “fumed oak.” This was a treatment that was first used during the Arts and Crafts movement and by Gustav Stickley in the early 1900s in the Craftsman period for Mission style furniture by exposing white oak to the vapor of anhydrous ammonia in a sealed chamber (this chemical process is highly poisonous). This process produces a beautiful aged brown color (throughout the entire thickness of a fumed board). Europeans were already using this process in the late 1800s after accidental discovery when it was noticed that installed oak boards and beams in horse stables turned color (from the ammonia present in horse urine). Fumed oak in the EU is referred to as “smoked oak.” This process is still used in controlled environments, but due to the dangers, is not used on site-finished floors.
Other chemicals have also been used in the past to chemically alter the color of wood, but most of those were seriously poisonous and are not used anymore.
Another process that has been used by artistically inclined woodworkers is by using a concoction called iron acetate, which is homemade by putting steel wool and white vinegar in a jar and allowing this to “brew” for a certain amount of time. The resulting iron acetate liquid is then filtered and applied to tannin-rich wood to “ebonize” the wood.
Since wood produced from one species typically has varying levels of tannic acid from one tree to another, one must be aware that the results may vary wildly from one board to another when using chemical reactive stains. This may be desirable and provide an aesthetically pleasing result with varying degrees of color variations within a wood floor. However, if a more uniform color is desirable, then it is obvious that the use on a chemical reactive stain may not be the right choice. In that case, it is better to select a standard stain or a combination of dye and stain.
One important fact about using chemical reactive stains is that the initial derived color will change over time and mellow out, it is normal and to be expected that color fading/change will take place.
When wood has been stained, dyed and stained, or has been treated with a chemical reactive stain it needs to be finished to protect that treatment.
As long as that treatment has been allowed to thoroughly dry, finishing is typically no problem. However, with chemical reactive stains, one must be cautious with using a water-based finish over that treatment as most waterborne finishes have an additive in their formulation that is known as a “PH balancer or adjuster,” which can chemically react and completely change the color of the reactive stain result. It is best to consult with the selected finish manufacturer and inquire which “tannin block sealer” is most effective in combination with the selected finish and next test the effectiveness of the whole finishing system before commencing with completing the floor in question.
Hard Wax Oil and Penetrating Oil Finishes
This group of products includes products that are available as a “stain and finish” all-in-one product. These products provide a color and finish within the same system. Color options may range from one manufacturer to another, and are often just as diverse as many dyes and stains (with more than 60 color options to begin with). In addition, there are optional pre-treatment products available from some of the manufacturers of this product category that raise the decorative color options and effects exponentially.
Understanding how to use a variety of finishes is an excellent way to offer your customers a unique look and feel and can set you apart from your competition. The NWFA Intermediate and Advanced level schools also give students the opportunity to learn about these different processes and play with some products that otherwise you may not have the time or ability to try. Full details on education opportunities are available to NWFA members at NWFA.org.
Johannes Boonstra is MI Territory Manager and Industrial Finishes at Rubio Monocoat. He can be reached at firstname.lastname@example.org.