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The previous owner told me that during the last winter when snow melted, water got in the basement through the drywall and he had to wipe dry the floor. Last year we had one of the worst winters on record (New York City).

I have a closet where a piece of the drywall (2x3 ft) has some black spots on it and water marks, but the rest of the drywall seems fine. The basement has regular drywall (not the blue one).

The basement doesn't smell musty or bad at all and I have not seen water coming in since then. I am planning on pouring concrete on the outside to take care of water that might be seeping through to the foundation.

If I just remove that small piece of drywall that has some black spots (mold?) on it, should I continue ripping off the rest of the drywall to look underneath? It would mean I would have to destroy the walls etc. what is the best route especially since the basement doesn't smell and I haven't had any issues since and the rest of the walls seem fine.

When I replace the drywall should I spray some stuff inside to kill the mold?

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  • I would remove several inches beyond the mold. also any insulation that is wet will hold the mold that needs to go also. You may want to leave it open to identify where the leak is and dry out.
    – Ed Beal
    Dec 23, 2015 at 20:06
  • I doubt there is any insulation, this is a 1920 building, it is all crumbled mortar inside. I will take a look though. Should i spray some mold killer in there?
    – tencijup
    Dec 23, 2015 at 21:56
  • I have used bleach and water mix with good results for the mold. The smell lasts a long time 1 cup bleach 3 cups water works well but wear old clothes and gloves. There are some commercial mold killers that don’t smell bad but are quite expensive compared to bleach.
    – Ed Beal
    Dec 23, 2015 at 22:26

3 Answers 3

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The industry standards, the ANSI/IICRC S520 Standard of Care for professional mold remediation, generally stipulates removal of 24" around the visibly moldy area. We would also generally remove any other wet drywall. If you see visible mold on the room facing side of the drywall, the likelihood of the problem being worse inside the walls is high.

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Fix the leak first before fixing any water damage. You should hold off on any interior repairs until you are sure the leak is fixed.

It is important to know where the water is coming from. A concrete apron around the outside may not be sufficient. You may need to move water further away and use a french drain.

Hydrostatic pressure will force water through concrete. If this occurred during a snow melt or heavy rain it is possible the water table was raised. In this case, you would need a french drain or sump pump in the concrete slab. Read for more information on hydrostatic pressure http://www.wagnermeters.com/flooring/rapid-rh-concrete-moisture/hydrostatic-pressure-isnt

  1. Remove the drywall several inches above the mold to expose the wall.
  2. Remove and discard any insulation.
  3. Clean the wood and/or concrete with a detergent or biocide. Let it dry completely. Follow EPA guidelines. http://www.epa.gov/sites/production/files/2014-08/documents/moldguide.pdf

Fix the leak and wait to ensure water does not return. Otherwise, you'll be ripping up your repair job.

  1. After the leak is fixed replace insulation, drywall, patch and paint.
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  • Link to the EPA guidelines doesn't work
    – drewish
    Jul 1, 2017 at 22:28
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This was a long time ago and well it is just a spot. You are actually probably rounding up more mold by removal than leaving it there - without water the mold is harmless - it lies dry and dead.

A remediation company would discard 12" around it and any insulation in that realm - maybe going more than 12" if seemed to be previously wet on inspection.

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