We just removed some molding from our floor only to reveal some kind of black substance that looks like dirt. We are not sure what it is. See the following photograph.

Black substance underneath molding.

  • Some more information would be helpful. Is this near a sink or some other source of water? If the area damp now or occasionally? What part of the world are you in? Is it usually humid? Do you use a dehumidifier or AC when it is humid? How old is the house? Etc.
    – Yehuda_NYC
    Jan 30, 2018 at 15:07

1 Answer 1


That appears to be black mold affiliated with a water leak or a flood. If a flood you need to have mold mitigation done by a qualified mold company. Drywall removal will be required as the mold you see is coming from the mold on the back of the drywall. Mold loves cellulose as a food so the paper backing on the back of the drywall will be completely covered in mold. If a flood situation it is recommended to cut a minimum of 1 foot of drywall above the noticed mold. However the paint can hide the evidence of mold and can be 4 foot or higher that needs to be removed. After removal in a flood situation it is recommended to use a disinfectant grease removal soap and scrub all areas affected to include the entire home. I clean a minimum of 1 foot higher than flood level. . I use Pinal lavendar sold at home depot as it has a nice smell. Then dry the home or area to a maximum of 50% of wood moisture measured with a moisture meter. You can buy this at home depot for about $30.00 After reaching 50% moisture then spray all wood down with anti microbial mold killer. Soak it down completely 3 times over 3 days no fans, no dehumidifiers. After 3 days then turn on fans to create a circle of wind in each room leading to a dehumidifier in each room. For entire home floods, you will need more than 1 dehumidifier. Recommended is 1 per room. So in many cases a mold control company is cheaper as we own equipment. It is also recommended to have a Hepa Air scrubber to remove airborne mold spores. After the wood reaches a level of 10% or less, you can install new drywall and insulation. However I require that my customers continue to dry under normal AC or heat for 1 week after certification. In cases of clean water damage like fire or water leak you can paint the studs with antimicrobial paint. In cases of flood damages, I do not recommend the paint unless you allow the home to dry out 6 months or more prior to painting and closing the walls. Flood bacteria takes more time to allow the antimicrobials to penetrate to core . And if you paint to soon...you will have structural failure from dry-rot bacteria (Fusarium sambucinum) prematurely.

  • 2
    Welcome to the site. You have a lot of good stuff here, but it's not inviting to read as a wall of text. Consider breaking it into paragraphs.
    – fixer1234
    Nov 26, 2017 at 3:07
  • Limitations are in the spaces when adding a paragraph. And then you get to read multiple posts. The words are readable and the information is accurate. So your English and grammar lesson is really pointless to a question of mold... Nov 28, 2017 at 0:20
  • Include this at the end “or it could be nothing more than harmless discoloration from a puddle of dog pee that served under the base board years ago”. Your answer is so far down the worst case scenario rabbit hole that I think I will save it’s a hilarious example of how the internet cannot be relied on for important diagnosis of anything.
    – Kris
    Dec 30, 2017 at 12:22

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