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Bleaching mold on sheathing?

edkrause | Posted in General Questions on

I’m building our house in Wisconsin, where we had a very wet June with 10 inches of rain while framing. The interior side of our 1/2″ plywood sheathing has dried but has developed spots of mold. I’m considering misting it with a bleach mixture and letting dry well before insulating, rocking etc. The finished wall system will dry to the exterior, with 3″ of Roxul Comfortboard IS on the exterior and Roxul comfort batts in stud cavities.

Any opinions on whether this is necessary? If yes, how strong should my bleach solution be?

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  1. user-2575529 | | #1

    Not sure about using bleach but there is a product called Concrobium that works well for getting rid of mold around your house. Home Depot sells it by the gallon and you do not need to dilute it. Just spray it on.

  2. Expert Member

    I've had very good results with Concrobium too.

  3. user-1137156 | | #3

    Much better than bleach ! 1 cup 20 mule team borax/ quart of water. Removes and kills the mold and leaves borax residue when it dries reducing the chance of future mold growth.

  4. jinmtvt | | #4

    i second concobrium ...
    used it in HVAC systems and works flawlessly

    mostly neutral an natural ingredients

    not dangerous to humans and coats the surface with a salt polymer in which the anti mold agent is preserved

  5. edkrause | | #5

    Thanks much, everyone, for your suggestions.

  6. user_953789 | | #6

    Our firm designed a house in Houston that is under construction right now, and I found this thread because have also had a wet summer that has resulted in mold and mildew on the home's framing. The contractor recently sprayed Concobrium on the problem areas and wants to start installing rigid insulation right away. We are concerned that he should wait until the product has dried before he begins the installation, but he is eager to keep the construction schedule going. What is best practice for addressing the mold issue before/during rigid insulation installation?

  7. charlie_sullivan | | #7

    Certainly waiting for drying is better, assuming the conditions are such that it will dry. What's your overall wall construction? 2x4 or 2x6 stud wall with fiberglass in the stud cavities and sheathing and then XPS (blue board) on the outside? Is the sheathing up already?

  8. Expert Member
    Dana Dorsett | | #8

    If the stud bays are open to the interior, with no insulation or wallboard it may be just fine to put insulation on the exterior now, and run dehumidifiers on the closed-in shell for a week prior to insulating the wall cavities. But it's better to measure rather than guess.

    Run down to the box store and buy a $30-$50 two pronged wood moisture meter. If the sheathing measures over 30% anywhere on the exterior (test in at least 3-4 places on each side of the house) , wait until it's in the mid-20s before putting up the exterior foam. Then when it comes time to insulate the wall cavities, make sure the sheathings & studs are 20% or less inside the cavity before going forward on that.

  9. user-347767 | | #9

    Thanks for asking this. I'm in the exact same situation in west central Wisconsin. It feel like a rain forest this year. Our excavation partially caved in over the footing due to rain.

    I've been hugely disappointed with the quality of CDX plywood. I need to replace at least 10 of the roof sheets due to delamination and bubbling. It's frustrating to pay extra for the plywood and get bad quality.

  10. dburgoyne | | #10

    In addition to spraying the solution mentioned above on the molded spots, I used a scouring sponge and scrubbed off any mold residue.

  11. edkrause | | #11

    Rather than buying Concrobuim after reading suggestions, I mixed my own using Arm & Hammer Washing Soda which costs less than $5 a box. Washing soda is powdered sodium carbonate, the active ingredient in Concrobrium.

    I spayed it on on with a sprayer and quickly scrubbed it a bit with a broom to help the sheathing absorb it evenly. Then I let it dry uninsulated as I worked on the exterior of the building. Being an owner/builder with part-time help, this was easy for me to do; the contractor who wants his crew to cruise along may find it more difficult.

    It is my understanding that the sodium carbonate residue will inhibit mold growth if the sheathing isn't as dry as it could be or if the sheathing gets wet in the future.

  12. BobHr | | #12

    I dont know if I would worry about a little bit of surface mold. You will have way more exposure to air borne mold on a daily basis. If that existing mold grows and causes problems you have much bigger water/vapor management issues. Concentrate on air, water and vapor barriers.

    The 3 things to remember about mold are mold spores are everywhere. That food sources for mold are everywhere (wood, drywall paper, dust, etc). So you are going to have 2 of the 3 things for mold to grow. The last thing is water/moisture is needed for the mold to grow. Water/moisture is the one thing you have some control over. Mold will not grow if you keep it dry.

    On the other hand you can clean the mold that is there but by the time you close the wall there will be more mold spores in there plus any air leak will introduce even more mold spores. If you dont control the water/moisture level you are going to have growing mold. Control the water/moisture and you will not have a mold problem.

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