Mold Testing by Inspector

I started my business in 1994, before mold became known as a public health issue, so I had about 7 years experience before the mold industry started to get organized.

To be credentialed, I took the mold inspector training in the early 2000s. At the class I attended, the students were essentially taught to be lab technicians. We were taught to do a visual inspection, and if we saw anything that looked like it might be mold, to take a swab or tape sample and forward it to the lab. We were also to take a spore trap test on each floor of the house, probably with the exception of the attic, plus the outside. That’s it – 4 or 5 samples from the average house (whereas I’m taking 40-60 on my inspections, usually without any lab fees but including photo-documentation of mold growth).

During one lecture, the student next to me leaned over and whispered, “Forget this mold inspecting. I’d rather own the lab.” He got that right.

Labs are fine as a tool when you need them. The problem with using labs during mold inspections is, however, that when all samples are sent to a lab, it’s prohibitive in cost to take as many samples as might be needed.

Another problem is that there can be high levels of mold that are not visible to the naked eye, so someone who goes just by what is visible may miss a lot of mold.

Therefore, if you plan to have mold testing by an inspector, be prepared that mold likely may be missed. You may want to pick up the slack with your own do-it-yourself testing before the inspector arrives. You may need to guide the inspector to where to sample (if you should need lab confirmation for legal purposes or if you want to be sure that remediation doesn’t miss some area of mold growth).

It makes sense to me that homeowners want the sources of mold growth gone from their homes, not to have inadequate satisfactory lab results that they can use to paper their walls.

While high school students can easily learn to use a microscope, professional mold inspectors apparently cannot. This is a serious shortcoming in the mold industry, in my opinion. You are paying good money to find out if mold is growing in your home, and the least that should be done is for the inspector to bring the tool that would reveal invisible mold.

Types of air testing

Although I find tape-sampling with a microscope invaluable for finding invisible mold, I almost always take air samples, too. When having mold testing by an inspector, the usual type of air sampling done is called “spore trap testing.” Spores are trapped on a sticky surface and the test kit is forwarded to a lab for counting. Some inspectors, myself included, prefer culture plate sampling, because it is better for diagnostic purposes. With culture plate, you can see the type of mold that grows out from trapped spores.

For an example, with spore trap testing, you might be told that there are 49 Aspergillus/Penicillium-like spores in the basement sample and 27 Aspergillus/Penicillium-like spores in the first floor sample. With culture plate testing, you learn more details. There are 49 Penicillium spores in the basement and 27 Aspergillus spores upstairs, pointing to two sources of mold, whereas the spore trap results suggested one source that spread upwards.

Spore trap testing and culture plate testing compared:

  • With spore trap testing, results are available faster, because nothing has to grow.
  • Counts are usually higher with spore trap than with culture samples, because with spore trap testing, both live and dead spores are counted, while with culture plate sampling, only live, culturable spores get counted. “Culturable” means the spores that will grow on the common culture medium. Spores may be present that don’t like the common culture medium, and they wouldn’t be counted.
  • Culture plate sampling is better for diagnostic purposes, because you can track the kinds of mold, especially those with spherical spores, such as Aspergillus, Penicillium. and Trichoderma. Spore trap lumps all the spherical spores together.
  • I study culture plate samples in-house, so I am not limited in the number of samples taken. Usually, every room is sampled, including the attic and basement, plus a few air ducts, and exterior. It is not unusual to sample 15 or more locations. With all this data, finding sources of mold and gauging the degree of cross-contamination are facilitated. At times taking so many samples may be overkill, but I’d rather have overkill than take too few samples. My clients agree with this position.
  • Lab fees are usually pretty close for each type of testing.

Question: I’ve heard that air sampling is a waste of money. Is this true?

Response: Sometimes air sampling doesn’t pick up on the mold, but usually it does and provides useful information. To me, air sampling is an important tool. I like to do at least one spore trap test in the basement of a house on a pre-purchase inspection.

(Industry guidelines call for one sample in the basement, one on each level of the house, and an outside sample. Sometimes we do that. Sometimes the prospective purchaser says that they won’t be negotiating but just want a basement sample done for their own information. One sample costs a lot less than four samples. But if legal use could be made of a basement sample, then have all four samples done, or you will have no reference point for understanding the basement sample. Your inspector could be challenged as not knowing what he is doing, for that matter.)

The microscope remains my favorite tool, but air sampling can pick up on issues that the microscope misses, and vice versa. Read the story below for an example where air testing failed to detect significant mold growth, but the microscope revealed multiple areas with growth.

Story: A two-year-old large house was inspected at great cost by an inspection firm with a top reputation, and nothing was found.

My client had moved into a brand-new house, but was unable to live in the house. In fact, he had to dress up in full hazard-protection suiting to even enter his home. He had hired what he thought was the best testing company in the state and had paid them a lot of money to do extensive testing all over the house. No mold was found.

A friend told him about my service with an on-site microscope. He had already hired the best, and they had failed to find mold, so why would he want to hire me? We talked back and forth occasionally over the span of a few months before he finally bit the bullet and scheduled an appointment. He had to do something, since he couldn’t live in his house.

I set my microscope outside on a picnic table, since he couldn’t enter the house. By the time the day was over, I had tape-sampled 110 surfaces and found mold growth on six of them. Here’s where I found the growth:

  • The basement ceiling joists and subflooring were covered with Aspergillus, even though they look perfectly clean to the naked eye.
  • Pressed wood shelving in the garage was covered with Aspergillus.
  • Aspergillus and Stachybotrys were found in flooring under potted plants that had been over-watered.

At the end of the day, he gave me a check and shook my hand with these words, “I felt I got my money’s worth today.”

  • Lesson #1: When inspectors don’t work with microscopes, they don’t learn all the common places to look for invisible mold growth. Inspectors are trained to send tape or swab samples to a lab for suspect areas, i.e., areas of discoloration that might be mold. It gets too expensive to test all the suspect areas that have no discoloration. I can test wherever I want, even 110 places at a home, since I bring along a microscope.
  • Lesson #2: There are different variables as to why and when mold releases spores. Air samples don’t always pick up on significant growth. The air sample taken by the previous inspector in the basement showed no mold, but I found the whole basement ceiling covered in Aspergillus.

Question:  If mold isn’t giving off spores, if the air sample results are good, should I be concerned about mold growth?

Response:  Most assuredly you should. Growing mold gives off gases, and these gases are biologically active and can spread through your home. Your goal should be to have no mold growth in your home. Look at the man in the 2-year-old house described above. His initial extensive lab test results were all satisfactory, but he couldn’t enter his home without being fully suited up in protective gear. He wasn’t reacting to particulates apparently, but to gases given off from areas of mold growth.

I find air sampling useful. It even sometimes points to an issue that tape sampling misses. But overall, the microscope is my most useful tool at a house.

Story: “Call May”

I had done this inspection described above before I took a mold inspection course. My business was started in 1994, seven or eight years before courses were even available, so I had a jump on the industry. From my science background, I knew how to use a microscope, and it seemed a no-brainer to use it to look for mold of my clients’ homes.

As I sat in the mold inspection course, I think my blood pressure must have been going up. I wouldn’t know how to interpret the degree of contamination at a house based on the minimal testing that this instructor was recommending. I wouldn’t have felt that I was adequately serving my client if this testing protocol was all that I was doing. (Bear in mind that this is the way mold inspectors are being taught still today – no microscope!!)

So, I raised my hand and shared the story that I just told you about the two-year-old house above. What does the instructor say to the class? “You are only doing a screening inspection, so if you find something that looks like it needs a more in-depth approach, call May or someone similar to her.”

“A screening inspection? A screening inspection?!” Those were my thoughts. I wonder how many homeowners and tenants who put out good money for a mold inspection think that they are just getting a screening inspection? I’ve already demonstrated the inadequacy of a visual inspection and sometimes of air samples, too. Given the choice between a screening inspection and my on-site use with a microscope, which would you choose?

I did an inspection for an apartment dweller who had had leakage from above in one room. With the microscope, I was able to report to her that tape samples from under base molding on all the walls were positive for mold, and that the room required some degree of demolition of walls and probably the ceiling, too. As often happens, the landlord sent in his mold inspector. The client later told me that when the client saw what landlord’s mold inspector was doing, she said to him, “Pardon me, but I don’t think you’re doing your job.” Unfortunately, he probably was doing his job, for a “screening” inspection. His (wrong) conclusion was that the window air-conditioning unit was responsible for the mold.

Another limitation of room air testing: hidden mold in wall and ceiling cavities

If mold is growing in wall or ceiling cavities due to past water leakage, that mold is not going to show up in room air testing. Mold spores can’t pass through solid drywall. In such a case, the inspector should know to drill a hole and take an air sample in the wall or ceiling cavity.

I typically don’t use the words “a lot or a little mold” when talking about levels in cavities. A little mold can give off a lot of spores, so we don’t know whether there is a lot of mold present or only a little. I use the words “footprint of mold growth” when air samples are positive from a cavity sample. The cavity may be opened up by a remediator and not much mold found at all, or there could be a lot of mold. You won’t know for sure until the area is under containment and negative pressure and opened up.

Bear in mind that there is almost always going to be a little mold in lower wall cavities. These are unconditioned spaces, with bare wood and wood product surfaces … dampness and food for mold. Insulation typically would stop significant migration of mold, unless there is a leak, and the water cannot dry out quickly.

Tip:  What if there is a leak? The best plan is to remove wet building materials before mold can grow, before a repair job turns into a mold remediation job. Check with your homeowners insurance about this right away.

Warning: If the inspector cuts out a hole, and there is significant mold on the back of the drywall and in the cavity, there is risk for mold particulates to be spread into the room air. Cutting out such a hole in a high risk area should be done under containment.

Tip: If you have an old house, and the walls are plaster, smile, because mold doesn’t like to grow on plaster. If there is old insulation behind the plaster, water intrusion may cause mold growth there, or mold might grow on the paint on the plaster. Too bad all our houses don’t have plaster walls. Mold likes wet drywall. Yum.

Tips for working with a local mold inspector:

  • Get your proper mindset. You are the employer and know more about your house than the inspector. You are hiring the inspector to do a job for you, to confirm or rule out the presence of mold in suspect areas. Decide ahead of time how you would handle the inspection if you were the inspector. Only then are you ready to hire someone. You need to be able to speak with the inspector as an equal.
  • Try to interview the inspector on the phone before hiring him/her. I’ve had much feedback about untrained and unprofessional inspectors. You may get one that you cannot work with. Ask them how they would handle this or that area in your home.
  • Ask what lab the inspector uses, and check the lab out on-line. View a sample report. Make sure you can understand the report and that raw counts are provided (to make your life easier when trying to interpret the results). Is the lab certified? Is the lab independent of the inspector?
  • Decide what you want the inspector to inspect and how you want it inspected…just one area or your whole home? If the latter, how will the inspector find invisible mold? You may do well to step in and send me tape samples before the inspector arrives.
  • Before the inspector arrives, think through the leak history of the house. Make a list and think about what testing might be done at each area. Follow the path of the water. Where the water went, you could find mold.
  • If folk in your home are mold-sensitive, think about where they report the most symptoms. Would any leaks be associated with those areas? How should those areas be tested?
  • If this is an insurance claim and the insurance company sends its inspector, you might need to get a second opinion from a mold inspector that you hire. First, however, think through what testing should look like for the area of concern and decide if you are comfortable with the tests that the insurance company’s inspector did.
  • I could say to ask if the inspector will bring along a microscope…but those inspectors are few and far between. You could try. To me and my clients, it’s commonsense for a mold inspector to arrive with a microscope. I don’t know how an individual would do an in-depth investigation without one…and why would you want to pay for anything less than an in-depth investigation?
  • Beware of inspectors and remediators who talk about “comparing inside counts with outside counts.” That comparison is irrelevant unless you know the species of the molds found inside and outside, and spore trap air sampling doesn’t give you the species. You might wonder if such an inspector knows what he’s talking about.
    If an inspector or company rep tries to pressure you with talk of inside vs outside counts, say, “Those numbers are irrelevant unless you know the species. Do you know the species from this spore trap report?”
    The answer is no, of course. Spore trap reports are incapable of identifying species. Aspergillus alone has 200 or so species. If one species is found outdoors and another indoors, there is no relationship between them. The inside Aspergillus spores did not blow in from outdoors.
  • Ask for aggressive sampling, not passive sampling, to be done. With aggressive sampling, dust is stirred up. The collection plate might be on the floor. With passive sampling, air is not disturbed, and the collection plate is typically on a tripod. You get more accurate results with aggressive sampling. Passive sampling can miss mold.
  • A company that has both mold inspectors and mold remediators is a company with a conflict of interest. Avoid such companies.
  • Learn how to interpret a lab report so that you are not at the mercy of someone else interpreting it for you.

How to interpret spore trap lab reports

  • Here’s an easy way to interpret most reports: Look for the raw count number for Aspergillus/Penicillium. You want a very low number, low single digits, for inside levels. If that number is elevated, then you should start looking for sources of mold.
    Also look for the presence of mold associated with leakage, especially if drywall remained wet for a prolonged time. The main mold here would be Stachybotrys. If the levels of Asp/Pen are low, and there is no Stachybotrys, you are probably ok.

Question: In my lab report, there are no raw counts, only the total number of spores per cubic meter. How can I understand those numbers?

Response:  Some labs report like that, unfortunately. However, you can still figure the raw counts. Look for the lowest number in the spores per cubic meter. (You might see the label as CFUs per cubic meter. “CFU” stands for “colony-forming unit,” which is a fancy way of saying “spores.”) The lowest number will probably be around 10. That would tell me that the lab found only 1 spore, but they estimate that if 1 spore were found in, say, 1/10th of the volume of a meter, then if you had a whole cubic meter, you’d have 10 spores, so they report “10 CFU/M3” even though only 1 spore was found. To find the raw counts for the rest of the molds, you would divide the total counts for each by 10. I prefer to work with the raw counts, because working with smaller numbers is easier…and less intimidating, too.

Tip: One trick some remediators use to intimidate prospective customers is to stress the counts per cubic meter, the larger number. Don’t be intimidated. Translate that number to raw counts. You may find that only one or two spores were found, and that’s typically of no significance. The exception to this is that if a spore of Stachybotrys were found, I’d want to know where it came from. I’d suspect that there was a source of growth in the vicinity.

When remediators act as mold inspectors:

Some mold remediators get in on the inspection end of things, projecting where mold is without any testing and providing an estimate of thousands of dollars to clean it up. I’ll talk more about this in the remediation section. This is unprofessional and unethical.