Failed Mold Remediation – What’s Next

Aug 23, 2020

What happens after you have a failed mold remediation? In addition to having the hassle of performing mold remediation in your property (not to mention the expense), some clients wisely decide to spend the extra time and expense to have a mold inspector verify if the remediation was successful.  This is to ensure that the property is back to pre-mold conditions.  

But then, there is a problem.  The mold inspector reports that the remediation clearance was considered a “fail”.  How can this happen?  What steps need to be taken to make the proper corrections?

It has been my experience that projects fail for one of four reasons.


If you find moisture of any sort in the area being remediated, that is a definite fail.  Puddles or evidence of damp surfaces mean that even if the physical mold had been removed, it will grow back soon.  Usually before any other part of the remediation is done, the moisture issue needs to be addressed first.  At this point the walls are usually opened up so it is critical that the moisture problem has been solved before the project gets a “pass”.

Failing to remove the mold growth during the remediation

Mold growth needs to be physically removed.  It’s not enough to “kill” it.  Dead mold can have spores that can still be released into the air and trigger allergic reactions.  If visible mold can still be seen on drywall, it needs to be cut out and properly disposed of.  If visible mold is observed on wood surfaces (See Photo #1 below), it can be roughed out with wire brushes or sandpaper (or media blasting on large projects).  

In my view, any visible growth is considered a fail.  If I find it, I instruct the remediation company to remove it.  In the photo below, a company actually thought that they properly cleaned the growth off the window frame.  They did not.

Photo #1 – Mold growth on window

Dirt and Dust equals a failed remediation

Another indication of a failed remediation would be a work area that is dusty or dirty. Mold spores are part of normal dust, so if there is a lot of dust in the area remediated, you can expect to find many spores. Furthermore, certain molds can feed on dust and dirt as a nutrient. We recommend having what we call a “White Glove Test”.  If you can move your finger across a surface in the area of containment and pick up dirt or dust, this would likely be a “fail” in my view.  The plastic sheets that constitute the containment will be taken down soon and the remediation company should not be leaving the client with a dirty (and potentially moldy) space.  Clean the work area of these particles using a HEPA vacuum.

Failed Air Sampling after a mold remediation

Finally, we get to the matter of a failed mold remediation when found in an air test.  Sometimes, our clients will be shocked to see that mold spores are more elevated after the remediation than prior.  How can that happen?  A number of items can come into play.  First, an air scrubber or negative air machine should be used during and after the heavy remediation to remove the excess number of spores that will inevitably be tossed into the air.  This almost always occurs with the cutting and removal of moldy surfaces on drywall or wood. Air cleaning should be a basic practice for all remediation companies.  Sometimes it is not. 

Second, if there is an excess level of spores from the air sample, it may be an indication that the air scrubbers did not run for a long enough period of time.  Oftentimes, having the scrubbers running for a few more days is all that is needed to properly clean the air. It can be helpful to move them around so that airflow patterns can reach “dead zones” such as corners.

Finally, when turning off the air scrubbers, the remediation contractor should cover the inlet to prevent any back pressure “burping” back spores into the area of containment. Since the spores are what we breathe in, they are of paramount importance in being cleaned.  

There are differences of opinion on whether air scrubbers or negative air machines should be run during any air sampling. That is a complex issue that we’ll need to cover in a different blog post. 

Photo #2 – HEPA air scrubber

Additional steps

When faced with a failed post remediation test, I would also follow these recommendations.  

Wipe down all surfaces within the work area with a damp cloth. Replace the cloths frequently for a thorough cleaning of the work area.

HEPA vacuum all the surfaces within the work area.  Again, this helps remove spores from the containment area.  The use a Swiffer cloth might also be helpful in passing clearance.

While HEPA air scrubbers are running, it is generally a good idea for the air inside the work area to be agitated to get any remaining spores airborne.  This can easily be done with a portable fan that is blowing directly into the area of containment.


When I go on post-remediation verification assignments for mold, I am often shocked at how often I see botched jobs.  This is where clients see how important it is to have a professional perform an inspection and test both prior to and after the remediation.   This helps both the clients and the remediation companies.   An independent third party professional can prove to be invaluable in letting you know if remediation was successful.  With all the money that’s spent, why leave anything to chance?