I was called by a flooring contractor to look at something strange that happened after he had refinished a white oak strip floor. After sanding one small room, the contractor was waiting for the water-popping to dry before staining the floor. As he loaded his equipment for the trip home, he looked over his work to see how the floor was drying. It wasn’t long before he noticed the joints were beginning to look charred, or burnt. A dark, black discoloration that had not been there moments earlier began to appear right before his eyes. He and his customer looked over the floor in astonished concern. The other flooring in the same downstairs level of the home looked fantastic. The homeowner questioned what her floor pro had done wrong. He questioned whether he would get paid. It’s how these things go.

They sent me pics from the job. With my own hypotheses rattling around in my woody head, it didn’t seem like this would be too difficult to sort out, but it also looked like a mess for the puzzled contractor. Following are my preliminary questions and the answers I received:

How much of the floor has it?

Just this one small room in the back of the home, 10 x 12 square feet.

What were your steps?

The customer wanted a medium stain, so we water-popped the floor to allow the color to penetrate more evenly and put down a fast-dry Cherry and Puritan Pine stain, and then three coats of single-component water-based finish.

And when did the black discoloration become a concern?

Just as we water-popped.

Why did you keep going?

We ran out of time. Out of the whole job it's like 120 feet.

The color you are seeing, was that the color of the floor before you sanded it?

No, but the existing floor was stained—a Provincial-like tone. It sanded fine everywhere, and the floor where it happened looked good just like the other rooms, but then only this room turned black.

Were there any pet stains? Any distinctly foul odors while sanding?

No. We’ve gotten that before, but not here.

With what we know at this point, and using the photos … what do you suspect may have happened? Post questions. I’ll answer them. Ask away. Bring it, floor pros!

See Part 2 of this post here.

See more wood floor mysteries from Stephen Diggins:

Wood Floor Mystery #1: The Spreading Black Spots

Wood Floor Mystery #2: The Poly That Wouldn't Stick

Wood Floor Mystery #3: The Tale of the Half-Cupped Floors, Part 1

Wood Floor Mystery #4: How Did This Floor Get Like This?

Wood Floor Mystery #5: The Uniform Gaps

Wood Floor Mystery #6: The Case of the Crawling Finish, Part 1


Stephen Diggins works for Wood Pro Inc. in their Salem, N.H., branch as manager and training director. He has many years of installation, sanding, finishing, gymnasium design and technical consulting experience, which he uses to assist his flooring customers on a regular basis. With almost 30 years in the flooring industry, he has been a freelance columnist for magazine, newsprint and online medias and has conducted product seminars ranging from wood flooring to luxury vinyl tile.