What is causing these black lines in my countertop? A bug?

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Forum topic by MitRellim posted 09-12-2019 01:17 PM 350 views 0 times favorited 4 replies Add to Favorites Watch
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2 posts in 8 days

09-12-2019 01:17 PM

Topic tags/keywords: question bugs

I finished these countertops around a month or so ago. A week afterward, I began seeing these black lines. They are producing a bubble on the surface. These countertops were made from century-old wood (I was told Maple). They were finished with five coats of water-based poly. This particular spot is right next to the faucet. The rest of the countertop is fine. Thanks for any ideas and especially solutions!

4 replies so far

View WhyMe's profile


1175 posts in 2041 days

#1 posted 09-12-2019 01:36 PM

Did you seal the end grain of the hole that the faucet fits through and also the underside of the top? I suspect moisture has gotten in the wood and mold is growing in the wood.

View SandyK's profile


51 posts in 3933 days

#2 posted 09-12-2019 01:42 PM

My guess would be that some water got under the poly, and some mold is growing in there.
I have had water get under poly on an outdoor project which caused the poly to bubble up and turn into a milky white color.
I think I would have used mineral oil for a maple countertop. I’ve heard that you have to put many coats on when new, but less and less over time, similar to a cutting board/butcher block.

-- Sandy, Minnesota,

View MitRellim's profile


2 posts in 8 days

#3 posted 09-12-2019 01:49 PM

That makes sense. I didn’t think about sealing the hole, but I imagine that is the case. I will plan to remove the faucet, sand the wood down and hope that I can fix the problem that way.

View controlfreak's profile


144 posts in 82 days

#4 posted 09-12-2019 01:54 PM

Once I saw the proximity to the sink and faucet I had my answer. Sealing the endgrain of the holes would help but in the end water is an insatiable beast and will find a way in. Just think about how often your hands are wet or water splatters onto that area of the counter. I think in the end you will need to have a solid surface around the sink water zone and Maple if you like in the dryer areas. I did do well with mineral oil on an island butcher block surface but had no sink in it. I think slathering oil around the faucet would be a pain in the neck too.

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