Is this Mold? Please Advise

About six months ago, I built a reclaimed, rustic-ish dining table from reclaimed yellow pine. It is finished in minwax spar urethane (3 coats). The other day, I noticed some black spots along with some grayish "fogging" in one particular spot on the table top. The affected area is underneath the finish - not on top of it. I don't recall these spots being there when building the table. It is a rustic table so it may have gone unnoticed for some time as it was partially under a place mat at a spot that never gets used - and it also blends in with the rustic nature of the table in general.

Here is the spot I'm referring to.

Attachment 378898

At this point, I'm not even sure what it is. Is it mold? Could it be something else? What do I need to do to fix it?

Thinking it was mold, I researched online and found an article suggesting a solution of 20 parts warm water, 10 parts bleach, 1 part dishwashing detergent. I applied that to the area and let it air dry, as suggested, overnight. That did not seem to make a noticeable difference.

Can anyone help identify what I'm looking at and what I should do to fix it?

How did you apply solution on the area? Probably you need to send out finish and treat this area after.
Ed.

Looks like it just in that one board. It does look like some kinda of black mold I wouldn't take a chance haveing that around some molds are very poisenous. Cut that board out and add a new one.

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Originally Posted by Eduard Nemirovsky

How did you apply solution on the area? Probably you need to send out finish and treat this area after.
Ed.

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The article suggested a first attempt of applying the solution to the affected area and allowing it to air dry. The next step in the article... if no improvement seen, sand the affected area and re-treat. Looks like I might be down to that.

Why don't you check with a local college or health dept and have it tested so that you can make an informed decision about what to do. Likely you can send a small sample and see what is really going on.

Ok, if it is mold and you did not sand off the finish you just put the bleach on top of the finish and did not get to it. Sand it down (wear dust mask), treat again, or use TSP, and wait and see if it get's it done.

Refinish after you sure you got it.

Another question could be where did the wood come from. Did it have a chemical on it and you mixing with finish cause it to come out.

Good luck.

Mold needs water to thrive. It will not grow on wood which has been dried down to the moisture level which is achieved indoors. What do you know about the lumber you used to make this table? Was it construction lumber straight from the lumberyard? Or was it lumber that had been reclaimed from years of service indoors?

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Originally Posted by JohnM Martin

About six months ago, I built a reclaimed, rustic-ish dining table from reclaimed yellow pine. It is finished in minwax spar urethane (3 coats). The other day, I noticed some black spots along with some grayish "fogging" in one particular spot on the table top. The affected area is underneath the finish - not on top of it. I don't recall these spots being there when building the table. It is a rustic table so it may have gone unnoticed for some time as it was partially under a place mat at a spot that never gets used - and it also blends in with the rustic nature of the table in general.

Here is the spot I'm referring to.

Attachment 378898

At this point, I'm not even sure what it is. Is it mold? Could it be something else? What do I need to do to fix it?

Thinking it was mold, I researched online and found an article suggesting a solution of 20 parts warm water, 10 parts bleach, 1 part dishwashing detergent. I applied that to the area and let it air dry, as suggested, overnight. That did not seem to make a noticeable difference.

Can anyone help identify what I'm looking at and what I should do to fix it?

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Looks like someone wrote on the table top with a permanent marker and then someone tried to clean it off with alcohol and all they did was cause the marker to stain the wood. I 99% doubt its mold

I've seen the same thing happen to several different reclaimed wood tables. Never sure what it was, but I remember when I was a kid always seeing almost the same exact flaw in my grandparents dining room table for decades and it never grew or changed. I've noticed it in a few other tables since.

Interestingly enough, I was able to dig through some old cell phone pictures of the table while I was working on it. It looks like this was already present on the wood and I just never have noticed it. I think the finish might have brought out the colors.

Attachment 378918

I guess that still does not address the question of what is it and is it dangerous?

To answer some previous questions. The wood came out of an old cotton warehouse built in the early 1900s. It did sit outside in the weather for several months before I purchased it. Moisture readings were ~10% when I started the build and are still at 10% today.

It may be staining from iron which should show up pretty quickly. The best treatment for that is usually oxalic acid although chlorine bleach is also effective. In either case, the finish should be removed prior to treatment.

If the EMC is 10%, it is not mold, or at least the mold is not growing any more. So you don't have to do anything to the table unless you want to remove the color. To do that, you must remove the finish. I'd probably just sand the finish off, and keep sanding into the discolored area. But maybe bleach would help you. If you find the discoloration goes a long way into the wood, you have a decision to make. You could just call it good -- this is a rustic table. Or you could cut off that board, and glue a new one on.

I don't believe that is a mold stain. I would leave it alone and just keep an eye on it for awhile. It's sealed under the varnish so just get a good picture of it to reference in a few months to assure nothing is changing.

What ever it is doesn't change the fact that its unsightly.
The board should be removed if people are using the table to eat delicious barbecue. If it's a table to rebuild diesel motors then it's very appropriate.

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Originally Posted by Andrew Hughes

What ever it is doesn't change the fact that its unsightly.

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That would be my only concern. Fix it if you don't like the way it looks. Mold under 3 coats of finish seems completely safe.