Over the years, trade- and craftspeople have used many different chemicals to alter the natural color of wood flooring using a single chemical or a mix of chemicals. These chemicals don’t contain pigments but alter the color of wood by reacting with tannins that are naturally present in the wood. Strong corrosive chemicals have also been used to bleach out the natural color of wood. These chemicals can be liquid household bleach, pool bleach, and two-part bleach.
Chemical reactive stains like lye, iron-acetate, anhydrous ammonia, or commercially available fuming/smoking products, can change the color of the wood by reacting with naturally occurring tannins in the wood. Reactive stains create an aged/rustic appearance of the wood in a wide range of intense and unpredictable color variations in the wood that are difficult or impossible to duplicate with traditional stains.
The concern that often comes up is: do these chemical treatments potentially damage/weaken the wood fibers, and what other potential problems may surface? The answer to this depends on what type of chemical is applied.
Most of the time, a single chemical application may not do excessive harm or damage to the wood. However, with bleach (both single-step or two-part bleaching), repeated applications will break down the lignin that holds the cellulose fibers of the wood together. Consequently, this will weaken the wood structure, which can result in a layer of weak/loose fibers on the surface of the wood that may affect the finishing system you plan to apply.
Wood’s natural pH level is slightly acidic/near neutral, and the application of liquid household bleach shifts the wood surface to a basic/alkaline pH level, which can affect the applied wood finish.
Two-part bleach is made of hydrogen peroxide and sodium hydroxide. With this type of wood bleach, the sodium hydroxide effectively degrades and dissolves lignin (up to 90 to 95 percent of its content in the wood surface), and it can also decompose wood carbohydrates, mainly hemicelluloses. When the hydrogen peroxide component is mixed in, or applied over the sodium hydroxide component, it creates sodium hydroperoxide, which is very aggressive and effectively lightens and removes the natural color of the wood on/in the wood’s surface.
As mentioned before, a controlled single bleach application can lightly damage the wood’s lignin and cellulose fibers, but usually, this is not serious enough to cause finishing problems. However, repeated applications of bleach will result in too much weakening of the surface fibers and may leave a weakened base for any finishing system to be applied to.
Let’s look at reactive stains: These products typically do not weaken the wood’s lignin and cellulose enough to cause a problem. Reactive stains provide wonderfully aged/rustic colors to a wood species that contains enough tannins.
However, the colorfastness of reactive stains often is not very good, and many will experience fading colors with exposure to light. Some fade severely, some less severely, and fading may present itself quickly or slower over time. This fading issue means that the reproducibility of the original color is sketchy at best. So, that would be a serious issue when repairs, touchups, and additions need to be done down the road.
What it boils down to with any chemical reactive, is that most wood finish manufacturers will not recommend or endorse the application of reactive treatments before applying their wood finish. This is true for bleaches, and homemade chemical reactive brews. If one plans to apply a different product than what is recommended or manufactured by a finish manufacturer, it is the individual’s responsibility to test for compatibility with the wood finishing product of choice. And know that you likely won’t have support from the finish manufacturer if there were a failure.
To avoid potential problems, it often is a safer (and smarter) choice to follow the recommendations of the manufacturer of the selected wood finish.
Johannes Boonstra is senior technical manager for Rubio Monocoat USA. He can be reached at johannes@rubiomonocoatusa.com.
Excellent Article. It is always the best methodology to follow the manufacturer’s direction. If you follow the manufacturers directions and the project doesn’t work out, you have the manufacturer’s warranty to fall back on. Smart and simple are always the best policy. If you want to experiment with floor finishes you should do it on your own floors or write into your contract with the consumer that the procedure you are going to attempt is not a tried and true method, “but could look really great” ! Good luck getting the customer to sign that contract. We don’t always have to be creative and attempt to reinvent the wheel. Performing quality workmanship in a timely and professional manner will be more beneficial in the long run than creating an unusual finish. Good Luck! Be safe and Happy on the job.