Black mold behind shower wall

  • This topic has 42 replies, 30 voices, and was last updated 6 years ago by ChadM.
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  • #10154

    Hey guys,

    Have you seen this before?

    I gutted a plastic molded shower stall and found the 2×6 plywood sheathing stained with black mold. There was no ventilation fan, a “air” leaky shower light and the area is directly above the soffit baffle vent.

    What do you think caused this?
    What’s your solution for killing mold?

    ~ Rob at http://www.ConcordCarpenter.com

    Gilberts, Illinois

    Moisture trapped in an unventilated area will produce this type of mold. As tile setter, I see this on almost every tear out.
    Regular bleach will kill it. If you paint on a coat of Kilz or similar before you close up the walls again it will help to contain the mold spores and give less chance of return.


    I used Sporicidin┬« for mold and mildew remediation/restoration. It’s rated for use in institutional, commercial and home environments.

    ~ Rob at http://www.ConcordCarpenter.com

    Honesdale, PA

    I do a lot of mold remediation, first off bleach does not kill mold. Once you start scrubbing mold with bleach you are releasing spores into the air, if your work area is not properly sealed and set up with negative pressure, this will move millions of mold spores throughout the house. I have seen more people get into trouble with trying to treat mold themselves. Since there are thousands upon thousands types of molds, first I would always recommend a air quality test, once mold is discovered. This will classify the mold and give you a better idea what you are dealing with. Most molds can be encapsulated and you should not have any other issues. But you need to find and fix the moisture issue first.


    Thanks for sharing I actually thought bleach will kill
    Mold. Learn something new everyday
    That’s why I’m here

    Gilberts, Illinois

    I am NOT here to deny your information. You said you do a lot of
    mold remediation, I don’t. With that said, I took a class given by
    the Illinois EPA on mold. They said that bleach would kill mold spores.Sprayed on, it would not cause them to be airborne.
    You are correct in saying next step is to encapsulate it – that’s why I suggested something like KILZ.You are also correct in saying FIRST the reason should be addressed.

    Gilberts, Illinois

    Found this link about Mold. Might have information or links if
    anyone is interested.

    San Diego, CA

    Too much moisture can create an ideal environment for mold. Mold will grow on wet materials in 24 to 48 hours. Mold can be removed from hard surfaces like hard plastic, glass, metal and counter tops by scrubbing with a soap or detergent.

    Honesdale, PA

    let me clarify, bleach will kill some active mold cultures. However most people that clean with bleach do more damage than good. You have to contain mold spores, and scrubbing with bleach will do more damage than good.


    schluter Kerdi should have been used. Tile,cement board never stop moisture/water.

    Pittsburgh, PA

    Hey at least you dont have mushrooms growing from the grout. Thats what we had in our bathroom due to a leak in the shower that got behind the shower frame (glass).


    …so just to verify – do not use bleach to kill mold in these situations, or…??

    John S

    Dewey, OK

    I am not sure about now but 2 years ago HUD was requiring treatment of mold with a solution of 50/50 bleach/water. No scrubbing just spraying. When the solution dried you were supposed to cover with Kilz. This was for HUD owned homes being accepted and maintained after foreclosure. I saw lots and lots and lots of mold.

    On another note, in the 80’s insulators in OK were covering blown in insulation with plastic. Then the drywall was hung. Everybody thought they were doing something really great. Turns out in the summer the warm moist air from outside infiltrated all the way to the cool plastic. Instant moisture problem. Give it a a and it was instant mold. I have seen that countless times. I dare say there are few if any houses built during that time period that don’t have mold in them.

    San Diego, CA

    To remove and inhibit bathroom mold and mildew, pour a solution of 3 tablespoons white vinegar, 1 teaspoon borax, and 2 cups hot water into a clean, recycled spray bottle and give it a few good shakes. Then spray the mixture on painted surfaces, tiles, windows, or wherever you see mold or mildew spots. Use a soft scrub brush to work the solution into the stains or just let it soak in. More details about this can be found here.

    Birmingham, Alabama

    Wow, what a combination of lists!
    We will throw in our information also….
    We did research with the EPA and they said- Mist the area with a strong bleach, let it dry, that will kill 99% of the mold, then spray the area with germicidal (Lysol) and that will get the rest of it. I agree that spraying with an oil-based primer like ‘Kilz’ after it all dries would also be a great idea.
    Recall what was said above “mold can grow in an area within 24 to 48 hrs” Mold is in the air all around us the solution is preventing water from concentrating on a surface.
    Stop the problem before it starts.


    Mould cause due to excess of humidity hence it is essential to have better and ample of ventilation to reduce the moisture level. Mould stains badly and if mould removal is difficult to clean it yourself then you should hire a professional.

    Fayetteville, NC

    Wow good thread on mold and its clean-up. Good stuff here.

    Automotive Pro
    Fayetteville, NC

    In the Rice Fields, South TX

    Spray on bleach diluted 50:50 water to fully wet it and the adjacent area. A pump-up sprayer works well. While wet, really thick spots can be scraped off with a wide putty knife or plastic ice scraper to help the bleach get down to it. If it makes dust, it’s not wet enough. Let it dry and repeat. Don’t scrub and grind it in. When absolutely dry, cover it and the surrounding area with Kilz to contain anything left. Respirator and good ventilation suggested.

    Owatonna, MN - Minnesota

    When we had some floods around here, FEMA was suggesting 50 / 50 bleach and water to take care of and to prevent Mold. not sure if it is correct, but one would think they should be in the know. after all, “they are from the Government and here to help” the 9 scariest words in the english language


    Bleach WILL kill the mold but only on the surface. It will not penetrate porous surfaces like drywall. White vinegar and baking soda or Borax and white vinegar will penetrate and leave a protective coating so mold does not reappear. If you use bleach exclusively the chances of the mold reappearing are pretty good.

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