Understanding Black Mold

Mold can be a real problem and understanding black mold, the most common of molds, is the first step to managing a problem.  But first, you should understand that mold remediation is an unregulated industry.  Self proclaimed mold experts are often generous to themselves in their claims.

Most often the most common mistake is to treat mold with bleach.  While bleach will knock down, or reduce problems associated with mold, it will not kill it.  The other mistake in treating mold is to close up a cavity before it is dry.

Black mold needs 3 things.  Encapsulated air, moisture and dark.  It becomes dangerous when it’s in a high concentration that can reach toxic levels, but there is mold, even black mold, in the air we breathe.  This is much like lead in our water — there is lead most water pipes in urban areas but the goal is to have low enough levels so it doesn’t affect you.

How to treat it

  1. Treat it.
  2. Sometimes treat it again.
  3. Aerate the area.

Safety: Importance of a safe air source during application

You can’t rely on a respirator, even one for fine particulate.  You must have an outside air source.  You can use a SCBA (Self contained breathing apparatus) which is what firemen wear, a scuba tank and mask, or apparatus that will pump air into a mask from an outside source, creating constant air pressure with breathable air for the person doing the treatment.

If you don’t do one of these things, you will burn your lungs and any of your mucous membranes like in your nose, your eyes, your throat and lungs.  You can kill yourself.  Effectively if you use the process described below, you are creating chlorine gas.

Important Historical Background

Mustard gas was used in World War 1 and was commonly used as a weapon and even after the visible gas had blown away across a field, the gas was heavier than air and troops in trenches would often take off their masks when they could no longer see it.  Then our soldiers would take off their masks and shortly thereafter feel burning.  If it didn’t kill them, the problems associated with the gas attack would continue through their entire lives.

Effectively, you are creating a gas that has the same effect as mustard gas.  It is my hope that this short historical explanation will instill in you the importance of not taking shortcuts.  If you are uncertain of how to do this, hire a person who has worked with mold in the past.

Treatment: Chemical Mix and Application

Moisture of chlorine bleach, water and vinegar which is applied with a sprayer (usually a 3 gallon sprayer) and that releases the chlorine from the bleach which is the most effective.  The mixture will release the chlorine which is dangerous to mold but it’s also dangerous to people.  Water in this case is just a medium to carry the bleach and vinegar.  Use as little as you can to still cover the area.  The hotter the water, the quicker it will evaporate.  That’s a good thing because you want to leave the area open enough to dry so you don’t get another mold bloom.

Scrubbing may be needed if you have a porous surface like wood framing or concrete block.  You can’t leave a substantial amount. At that point you can dry it.  Once you see a white film on basement walls for instance, you know it is mostly taken care of.  There will likely be


There is no certification program or certificate that is available by the government.  You can get one privately through an educational agency but the only certification you can get is through them.  Yes, this seems ludicrous, especially with all of the attention black mold has received over the past few decades, but for some reason, the government has decided to be hands off on mold certifications.

This mix will result in burning, possibly permanently, your mucous membranes.


All the windows are closed during application so the solution and gas can have its maximum effect.  This should be kept closed for 30-60 minutes after the application.  Afterwards, the house must be well ventilated with fans blowing in.  Optimally for a few days, but in about 4 hours there will still be a scent of the bleach in the air but at very low levels in a well ventilated area.

Any pets inside will likely die along with the mold.  On the plus side, most mice and insects will die as well.  Remember, you are effectively waging chemical warfare against mold and anything living in the home.

In about 4 hours there will still be a scent of the bleach in the air but at very low levels in a well ventilated area.


There has been much talk about black mold but sometimes it’s just mildew or just a common mold.  Mold testing kits can be used but it must be an active bloom (versus dormant).

Adding moisture to something that loves moisture seems counter intuitive.  This is why it is important to run fans against the treatment process and not to enclose a wall until the area is dry.

Commercially Available Products

You can buy commercially available mold killers but they’re not as concentrated.  They require more treatments and they are more expensive.

Prevention and Mitigation

If you’ve had problems in your attic space, switching from passive ventilation in your roof to active ventilation will move air to dry things out — effectively starving mold of one of the things it needs to reproduce, encapsulated air.

The Danger of Over reacting

If you suspect there is mold, it’s important to not over react.  Ask yourself a few key questions.  Is there a moldy or musty smell?  If so, have you investigated the problem?  Have you taken a small sample and sent it into a lab?  Does your house have the 3 factors that help mold to bloom and propagate?  Before you start ripping out drywall and decimating your home, consider calling in a professional or two to get their opinions.  Don’t be afraid to pay for an inspection service, but be cautious about restoration services that have a financial interest in mitigating a problem that may or may not exist.

Black mold doesn’t like moving air and it does not like dry.  It cannot live in extended areas of sunlight or UV rays.  Take away the moisture source, kill as many spores as you can, and then air and sunlight (or a UV lamp) and you’ll be on your road to a healthier house.

Think about your house as a body.  If you’re concerned about being a little overweight, you don’t want to march into the doctors office and demand he do a quadruple bypass.  Not to mention the scars, the pain of healing can be a process you never recover from.


Jim McGuigan is a licensed general contractor in the State of Wisconsin.  He does not claim to be a mold expert but like all good building scientists, he surrounds himself with the best in the industry.  He cautions homeowners interested in addressing their mold issues to read the entire article and educate themselves on mold before hiring a contractor.

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