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  NOTE: May Dooley passed away in March 2024. This site will remain available as a tribute to her.

Mold Remediation

There are several objectives in mold remediation:

  1. To know where the mold growth is so remediation can be complete. Often during the course of remediation, more mold is found as areas are opened up.

  2. Since once demolition starts, a gazillion more mold particulates are likely to be released. The rest of the house has to be protected from contamination.

  3. The professional remediator will set up adequate containment, like a temporary room around the work area, with plastic walls.

  4. Inside the containment area, the remediator will set up negative pressure. A negative pressure machine is like a commercial-sized room air purifier, with HEPA quality filtration. (HEPA means that 99.93% of particulates 0.3 microns and larger will be removed from filtered air.) Instead of discharging the filtered air back into the room, typically at duct extends to a window or exterior door so that filtered air is discharged outside, instead of into the room.

    When more air is discharged outside then enters the work area, negative pressure results. This protects the clean areas of your house, because the direction of air flow is from clean to dirty to the filter and then outside. Little mold particulates can’t travel against the airstream.

    If there is no way to set up at duct to the outside, then the filtered air will be discharged into the work area. Instead of being and negative pressure device, the same device is now called an “air scrubber.”

  5. Professional remediators should take steps necessary to prevent the dissemination of mold particulates into clean areas of your home.

    For example: If the work area has a window or exterior door, materials removed through demolition can be wrapped and removed through window or door. However, many times the work area has neither a window nor door, and the contaminated materials must be brought out through another door.

    Here’s what that might look like with a professional company:

    • There is an ante room (like a smaller version of the containment work room) between the area of containment and clean areas. A worker from the work area would bag the material to be disposed of and bring it to the ante room. A second worker from a clean area of the house would enter the ante room, wipe off the plastic bags, and remove them for proper disposal. This approach prevents mold particulates from being released into clean areas during removal of contaminated materials.

    • Another practice for safe removal of contaminated materials might involve the company making a tunnel-like walkway between the work area and the outside. Again, the clean areas of the house are protected from mold particulates as contaminated material is removed. One professional remediator told me that it can take as long to set up containment, etc., as it does to do the actual remediation job.

    • Workers from dirty areas would remove their personal protection equipment in the anteroom before entering clean areas.

  6. You may have noted that these steps take time and meticulous attention to detail. You may get what you pay for. Will the mold remediation job be on the same level as asbestos cleanup, or will perhaps a less-than-professional remediator convince you that fogging or blasting or some other catchy idea will be adequate for remedation, collect your money, and then leave. If you are willing to pay $7000 for a fogging job, call me. I’d be happy to come and fog and collect $7000. I just won’t do any post-remediation testing, ha ha. (This is just a joke; I am not involved in the remediation end of things.)

  7. After containment and negative pressure are in place, demolition (if needed) will start. Contaminated materials are removed and bagged, or double-bagged, for proper disposal. If water staining or mold extends beyond what was originally thought, then the scope of the job may or may not have to be expanded, depending on what is involved.

  8. HEPA vacuum the entire area.

  9. Clean wood surfaces as needed. Many companies use chemical pesticides to do this, my recommendation is to use hydrogen peroxide, Benefect, or a similar least-toxic product. You don’t have to kill the mold if it’s going to be removed. It’s gone. Who cares if it’s gone dead or alive?

  10. Since I started in this business, I have been a strong proponent of using an encapsulant after cleaning. Think of it this way: the cleaning product is temporary. The encapsulant is permanent (unless, of course, there is a future water incident). An encapsulant is like putting a sealant or a paint on the cleaned surfaces. Here are some advantages of encapsulation:

    1. Encapsulation protects your investment against future mold growth.

    2. Encapsulants kill and seal in any residual mold from the cleaning process, as well as buried hyphal fragments.

    3. Many in the mold industry disagree, saying that if the remediation is properly done, mold will be killed and it won’t come back, as long as humidity is controlled. My response is simple: What if humidity is not controlled?

    If the remediator you choose to work with is not a believer in a encapsulation, you or your handy person or a painter can come and afterwards and just apply a sealant. You may even save money that way.

  11. Now that demolition, cleaning, and encapsulation are done, the final steps are cleanup of residual mold particulates in the work area. This is done through HEPA vacuuming and damp wiping, while the negative air pressure machine continues to run.

  12. After the remediator is finished and leaves, the negative air machine likely will be left to run another day or two. Then it should be turned off.

Post-remediation Testing

After the negative air machine is off for a day, post-remediation testing can be done. You should bring in an independent inspector for that testing. It’s a conflict of interest for the mold remediator to test his own work. We’re going to talk a little below about interviewing remediators, but let’s put the cart before the horse here and talk first about post-remediation testing.


As is typical, a visual inspection will first be made for surface cleanliness. Have tops of oil tanks, hot water heaters, etc., been cleaned? Are tops of cross-supports between ceiling joists clean? If debris is present, the remediation team may need to be called back before final testing. In the industry, sometimes this is known as “black glove” standard of cleanliness. If you ran a black glove over the surface, would there be dust on the glove? I don’t approach post-testing this way, because how could ceiling joists and other unfinished wood surfaces in a basement, crawl space, wall cavity, or attic be cleaned to this degree? They couldn’t, but there is a workaround with encapsulation - see below.

Tip: If unfinished wood surfaces are encapsulated, they are clean, even to black glove standards.


Now, to air testing. As noted elsewhere, least one study has shown that aggressive testing is more accurate than passive testing. When I write up a mold inspection report for my clients (for use with remediators), these are the points that are made:

  1. Post-remediation testing is to be done by an independent inspector, not by the remediation company. Not only is it a conflict of interest for a remediator to test his own work, but inadequate testing may result.

    For example:
    Samples may be taken while the negative air machine is still running;
    Samples may be taken next to the negative air machine, on a tripod, when the machine has just been turned off;
    There is almost a written guarantee that passive samples would be taken, rather than aggressive samples. That is, a sampler would be set up on a tripod, without stirring up dust.

    In all three of these examples, the remediator would be testing the effectiveness of the negative air machine more than the diligence of his team. It should be noted that even independent inspectors typically do passive testing, i.e., setting up a tripod without stirring up dust.

  2. Aggressive testing is to be done by an independent inspector. He may use the tripod, but he must stir up the air, starting from the floor, around the tripod. It’s easier just to put the canister on or near the floor and stir up the area by the floor. This type of testing provides a much better sense of the cleanliness of the remediated area and the degree to which mold spores have been removed.

  3. My guidelines suggest that post-remediation test results should show levels of Aspergillus/Penicillium-like spores in the low single digits for the raw counts, which would typically be under 100 spores per cubic meter. These numbers may be a little higher in unfinished areas.

  4. What if your lab reports come back significantly higher than these numbers? Will your remediator return and re-clean? Will there be an additional charge? Did you go over these issues during the initial interviews with remediators? (Do you also suspect that if you did, you might be labeled a potential pill and they would pass on the job, or up the estimate?) You may be navigating some treacherous water here.

  5. There are good and professional remediators out there, there are also many who have never really had their work tested to this degree, so they may be living with a false sense of security as to how effective their remediation process is. One owner of a franchised remediation firm proudly told me that the inspector who did their post-remediation testing never failed a single job. They had an unblemished record. I thought to myself, “That inspector doesn’t know where to look.” Now I would be more aware that probably passive sampling was being done.

Selecting a mold remediation firm

Some suggestions:
  1. Know what you want done, and see who will do it. This eliminates the companies that just want to come in and fog, etc. Look for a good match and someone who speaks your language.

  2. Ask about containment and negative pressure and their experiences with post-remediation testing.

  3. Do they charge an hourly rate, or a flat fee? (With an hourly rate, you know better how your money is being allocated.) I heard this long ago in remediation training, which I took for personal enhancement, but I don’t know what is common in the industry these days.

  4. Come to an agreement on what products will be used. Later, confirm that on-site workers have been informed of what products to use and have them on site. Will they be including encapsulation? If the responses that they spray with a mold-resistant product, a mold-resistant product is not an encapsulant. You want an encapsulant, even if you have to do it yourself after they leave.

  5. Beware of a charming sales representative; workers may not live up to what has been presented.

  6. Ask about the training and experience of the workers. How long have they worked for the company? If there is much turn-over, that may be a sign that they are working hard for minimal wage or higher, but not sufficiently higher.
    (Remediation is a hard, meticulous job, done right. Consider a generous tip for each worker at the end, if you can manage that and are happy with what they did.)

  7. What’s the reaction if you talk about aggressive testing and levels of Aspergillus/Penicillium-like spores under 100 spores per cubic meter? What is their policy if more cleaning is needed?

Part of our dilemma is that most remediators probably have never been queried like this. They may feel threatened and truly might not know how their work would stack up under aggressive post-remediation testing. I don’t have easy answers, but here is one story:

A client in central Pennsylvania had a mold issue from a leak. She hired a local company, and they make things worse. She hired a second local company, and the house became unlivable to her. I suggested a small, professional company from Brooklyn where they were willing to travel. And that’s what she did, she brought them in, they were three weeks at the house, but they delivered a house that she could live in once again.

The project was pricey, because now the whole house had to be remediated from the previous botched jobs, but she also felt that the Brooklyn fees were in line with what local companies had charged her. She had to add this final inspection fee onto her mortgage (or something like that), but she liked the house, want to stay there, and felt it was the better choice compared to moving.


Let’s stop a moment and look at fogging in more detail, because in some medical circles, it’s a big deal to finish off a remediation project.

Description: After a remediation project, many microparticles may be left behind, not removed by the negative air machine. As was mentioned before, many of these microparticles may be inflammagens, so it would be nice if they were removed. Gravity affects everything but here, the microparticles are so tiny that air molecules buffet them around and they remain suspended in the air, the very air you will be breathing.

But how to remove them becomes an area of controversy, if indeed they can be removed at all.

On the one hand, the argument goes that fogging would remove microparticles. Near the end of the remediation project, the negative air machine gets turned off, the remediator fogs with a glycerin-based product, the microparticles adhere to the fog droplets, and the weight of the drops pulls the microparticles down. Once the microparticles have settled in dust, then the whole work area gets wiped down with dilute alcohol to capture and remove the microparticles.

I was told by the developer of this process that medical test results are improved over when remediation was done without the final fogging/cleaning step. Who am I to argue with testing results?

On the other hand, several individuals who know a lot more about physics than I do have remarked that, nice story, but the physics doesn’t support this explanation of what is happening with the fogging.

Microparticles are so very tiny compared to a fogging droplet. Let’s say one fogging droplet was the earth and the next closet droplet the moon. There are a ton of tiny microparticles between them, most of which won’t be close enough to adhere to a droplet. The distances between particles, on these small scales, are vast.

Who am I to argue? I call it a case of “warring science,” and if a client wants this type of fogging done, there are remediators out there who could oblige.

We’ve actually touched on this subject before, on the Testing Options tab, when we spoke about PCR testing (ERMI, HERTSMI-2), and about some of the ethical concerns that can be associated with microparticle testing: It is likely that most houses would have some elevated readings. Does that mean that every house should be fogged and wiped down, all contents wiped down, if not discarded? That doesn’t make sense, yet that is what a purist reading the PCR results might lead to.

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