Wood Floor Mystery #11: What Do You Think Caused These Black Spots? Part 1: The Problem

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Hickor Baltic 4

Well, 2021 was insane, so let’s not go down that road ... Hardwood flooring is still boomin’ here in ’22! After moving a lot of flooring and recording a few podcasts, I am happy to report there are still flooring mysteries everywhere, and I’m back in the blogging saddle to sort ’em out and discuss them with my fellow floor pros around the globe, so let’s get to it!

A very bright and genuinely concerned woman from Canada, whom we shall call “Betsy” (because her name is Betsy) noticed small black spots gathering on her new prefinished hickory floors:

Hickory Baltic 3 Straight

Hickory Baltic 5Hickor Baltic 4

ClosetUpon Googling with very limited success, Becky came across a WFB article I wrote back in 2014, "What Causes Mysterious Black Spots in Wood Floors?" In that case we discussed unidentifiable “black spots” on a hardwood floor—spots I was able to match and compare with an inspection of my own. That issue turned out to be what I termed at the time “MPCC: Metallic Particle Corrosion Contamination.”

Through the WFB website, Becky found my contact information and emailed some photos and a description of her situation. The game was afoot! Ah, It’s great to be back in the game. Bring it on, baby… Here’s what she emailed:


I read your comments online. I am hoping you can help me.

I live in Revelstoke, BC. I recently built a small house with ETM hickory Baltic signature brushed engineered hardwood floor over a concrete slab on grade (no crawl space). Black spots started

appearing July 2020 (I moved into the house December 17, 2019). They are getting worse… I am worried about mold. Any help is appreciated. Thank you! 



Let me point out a few items of concern as readers peruse the photos presented: The black spots appear to be uniform in size. In one photo it looks like a particle or granule has been crushed, leaving the core grayish colored and smearing a black streak across the board’s surface. Also, notice the particles almost exclusively appear in the open grain—the springwood—and not in the summerwood. There are several correct terminologies here; I’m a little rusty, so, fellow floor pros, please don’t bust me on these (but trust me, these are important).

So, I got this! Or so I think … where do we go from here and what are the likely causes and solutions to this paltry flooring dilemma? Look closely at the photos provided. Maybe read my original blog and reader contributions? I think you’ll be surprised what we’re gonna find.

And … catch our All Things Wood Floor podcast, and maybe we can start getting into our flooring mysteries in more depth with pros from around the world. Let’s see what you got floor pros, LET’S GET TO IT! 

(See Part 2: The Answer to this mystery here.)

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All Things Wood Floor, created by Wood Floor Business magazine, talks to interesting wood flooring pros to share knowledge, stories and tips on everything to do with wood flooring, from installation, sanding and finishing to business management.
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