With the increasing trend of natural and white (or lighter stained) floors, we’re also seeing an increase in the instances of “the mysterious black spots” showing up on these floors – especially red oak (though it has been reported on white oak to a lesser degree). Understanding that this possibility lies with every new install or resand, how can you best minimize this phenomenon causing issues for you and your customers?
Deal with Customer Expectations First
“Expectations” are always the #1 commandment at our schools, and this is a perfect example of why it should be yours as well. If you have a customer who wants their floor stained white or natural, let them know that these spots might make an appearance somewhere on their floor and that while you’ll do your best to minimize any reactions, it’s considered a natural part of their wood floor (i.e., character). When things like this are not covered up front, trying to explain them away afterward always comes across as an excuse to your customer and finishes you into a corner, per se. Discuss the possibilities and include descriptive verbiage about just such a scenario in your contract.
How Can You Minimize These Spots?
Water-Pop the Floor During Sanding – Because we know that the life-form deposits that cause these black spots are water-soluble, water-popping a new install or water-popping after the first cut on a resand should bring any potential spots to light. You also might want to spot-pop problem boards/areas between every cut. Because there is only x-amount of the dark spot material within each cell, the more you can bring out and sand off with each cut, the more significantly you will minimize any residual material from being drawn out once the stain, sealer, and finishing process starts. Also, remember that with successive cuts you may open up other cells that contain the blackish material, creating other spotted areas, though usually on the same boards.
Apply “Thin” Coats of Waterborne Sealer – We usually don’t push the “thin to win” theory when applying any sealer, as a proper coat at 500 square feet per gallon is already thin enough (about 1/1000” = one sheet of copy paper), but in this case, thinner coats will give you better results as you battle to minimize the devious spots. Again, due to the greater water solubility of the dark deposits, if you can reduce their exposure to water, you’ll get less pull, and the resulting initial sealer film will help to minimize any additional pull from succeeding coats; though you might have to apply two to three thin coats of sealer to give you the desired build you want prior to your finish application.
Spot touch-up with game line paint – Depending on the final look and color that your customer is expecting, any spots that are too dark (or snuck up in an unexpected area) after the sealer coats have been applied can be touched up with waterborne game line paint. You’ll have to work up the blend that works best for each floor’s final color, with light beige being a great place to start, then adding white or yellow/brown to take the color in the desired direction. As the spots tend to originate and spread from the soft grain vessels, touch them up with your paint blend like you would a stain repair, dabbing on the paint and feathering it out in the same direction as the grain/spot pattern with an artist’s brush. Good feathering is the key to making it look natural (as is a good color match).
Achieve the white color with sealer instead of stain – The application of white stain is not enough to seal the dark deposits into the vessels, and they typically are not visible once the floor has been sanded, so staining a red oak floor white may be a waste as any residual dark spots still will pull up through the stain. A better route would be to apply thin coats of white-pigmented sealer until the desired level of white is attained, which also will minimize the deposits from coming out as described above. Then, touch up any spots, as needed, with your paint blend and apply clear coats of waterborne finish over the top to protect it all.
This is the second part of the article, “Dark Spots Mysteriously Appear in Red Oak (Again),” which ran in the October/November 2024 issue of Hardwood Floors.
Why Not Use Solvent-Based Sealers?
While a solvent-based sealer would be more effective at preventing the black spot material from leaching back up to the surface, they will all turn the wood surface too yellow (even worse over time) to fulfill a white or natural look floor, as seen in photo B1 (natural, opposite page) and photo B2 (white stain, opposite page) that were both sealed with two coats of dewaxed shellac (OMU would be even darker and yellower); thus, our sticking to an all waterborne system when trying to troubleshoot this issue.
Give it time – A friend and great craftsman from the Williamsburg, Virginia, area, who first alerted me to the resurfacing of these mysterious black spots occurring on red oak while he was working on a historic museum job also reported back that after a year, the black spots had faded to an almost indistinguishable level – only noticeable on hands and knees if you knew what you were looking for. He also clued me into the game line paint method. So, this time element also is something to keep in mind while discussing expectations with your customers or trying to figure out the best way forward if they do pop up.
It’s always a heartbreaker to hear someone resanding a floor to try and resolve an issue like this, unnecessarily taking away from the lifespan of the floor when a little bit of time (and paint) might be all that’s needed to fix the problem and get everyone back to loving their hardwood floor.
Todd Schutte is the director of global eLearning for Bona AB in Englewood, Colorado. He may be reached at todd.schutte@bona.com.
