Mold Testing – Air Quality Lab Interpretation

by / Thursday, 14 February 2013 / Published in Environmental Testing, Healthy Building Inspections & Testing
Mold Testing Petri Dish Impactor

Mold Testing Air Quality Lab Interpretation

People with asthma and mold allergies are the first to ask about mold testing. Since their symptoms are primarily respiratory, it is only logical they ask for “air quality testing.” Other individuals looking for peace of mind or suffering much more severe symptoms sometimes also ask for mold testing air quality services. This blog is about air quality testing and some of the variables and limitations that should be considered in every mold testing job.

Part of our job is to help develop a mold testing air quality sampling plan specific to your project, and to help interpret the lab results in light of discoveries made during the visual inspection. I’ve heard mold testing described as “an art and a science,” and I agree with that sentiment. Since it’s not a federally regulated contaminant it has been a little bit of the wild west in terms of who tests, what they test for, and how the results are interpreted. For a customer – that should scare you! – because it has meant that anyone could call themselves mold inspectors without having adequate training or professional credentials to demonstrate their competence.

Mold Testing – When to Test Air Quality?

Most experts, including the EPA and California Department of Public Health, suggest only testing under very specific conditions. In general, a moisture and mold inspection by a qualified professional is far more useful in determining if a mold problem exists. However, there are some circumstances that warrant additional air quality testing. The most commonly referred to guidance for how to perform mold inspections and when/how to test for mold is the AIHA “Green Book,” Recognition, Evaluation and Control of Indoor Mold.

Mold Testing Air Quality

Mold Testing AIHA Green Book

Here are three general reasons that justify mold testing:

1) Determining scope of contamination.

2) Determine type of contamination.

3) Clearance testing.

Mold Testing – What Type of Air Quality Testing Method?

If mold testing is pursued, these are the three most common types of samples collected:

  • Air sampling: the most common form of sampling to assess the level of mold. Sampling of the inside and outdoor air is conducted and the results to the level of mold spores inside the premises and outside are compared. Often, air sampling will provide positive identification of the existence of non-visible mold.
  • Surface samples: sampling the amount of mold spores deposited on indoor surfaces (tape, and dust samples). Dr. Ritchie Shoemaker, MD is a strong believer in dust sampling using the Environmental Relative Moldiness Index (ERMI).
  • Bulk samples: the removal of materials from the contaminated area to identify and determine the concentration of mold in the sample.

In this blog we focus on air quality testing. There are four ways of air quality testing for mold:

  1. Sporetrap non-viable (non-culturable) sampling. While controversial, this is the most common type of “mold testing” we see performed in the industry. A calibrated pump draws a known volume of air over a greased slide. This is an “impaction” method of collecting spores. Based on a direct microscopic examination of a portion of the slide, the lab extrapolates how many spores are present per cubic meter, and can identify many common genera of mold. One weakness of direct visual examination is that some common genera, such as Penicillium and Aspergillus, cannot be differentiated and reported cumulatively. Another obvious weakness is that heavier spores, such as Stachybotrys, may be present but not aerosolized and therefore underreported if only air sampling is performed.
    Mold Testing Air Quality

    Mold Testing Handheld Sporetrap    Mold Testing Air Quality Testing – Alex Stadtner using pump and Sporetrap

  2. Pitri Dish-style, viable (culturable) sampling. The second most common type of air sampling for mold is also an impaction-style collector. A petri dish with a growing media is placed beneath a pin-holed cap and air is drawn over the petri-dish. The petri-dish is then incubated and visually inspected so the number of colony forming units (CFUs) of different types of molds are identified and counted. Common types of mold growth media are Malt Extract Agar (MEA), Potato Dextrose Agar (PDA), and Hay Infusion Agar. A strength of this method is that molds can be especiated. So in addition to differentiating between genera like Penicillium and Aspergillus, using viable (culturable) analysis you can identify if the mold is Aspergillus niger, or Penicillium marneffei. This can be valuable information since there are hundreds of species within each genera, and some are more toxigenic than others. Some weakness of this sampling method include the fact that different molds prefer different growth media, temperatures and moisture levels, but the lab will just use a “standard setting” unless instructed otherwise. So to get a more complete picture of the viable airborne spores in one space you may need to collect numerous petri-dish samples using different agars and to be incubated under different growing conditions. Some molds grow well under lab conditions, and others don’t. Some molds produce powerful chemical weapons used against neighboring colonies, which can influence the number of CFUs counted for both species.
    Mold Testing Air Quality

    Mold Testing Petri Dish Impactor

  3. Microbial Volatile Organic Compound (MVOC) sampling. When molds are wet and have food they grow. When mold is “eating” it produces metabolic byproduct gases known as MVOCs. Air samples can either be collected in a summa canister or sorbent tube, and the lab analyzes the air sample for a limited set of microbial VOCs. MVOC indicator gases include but are not limited to the following: Furan, 1- and 2-Pentanol, 2-Hexanone, 2-Heptanone, 1- and 3-Octanol, and Geosmin. Most MVOC scans are limited in that they do not analyze for every possible MVOC, and most MVOCs have not been directly tied to a single species of mold so extrapolating from just MVOC data is rather limiting. If you smell “musty” odors you are probably inhaling MVOCs. It’s a sign of active microbial growth and can be tested via air sampling. 
    Mold Testing Air Quality

    MVOC Testing for Mold

    Mold Testing Air Quality

    MVOC Mold Testing with Sorbent Tube or Summa Canister

  4. Mycotoxin Testing. Mycotoxins are secondary metabolites produced by fungi. These are basically self-produced chemical weapons wich can harm other fungus, and can also cause disease and death in humans. Although the primary concern for humans is for ingestion, inhalation is also of concern. Few indoor environmental consultants are currently testing for mycotoxins. The three most commonly analyzed mycotoxins include aflatoxin, trichothecenes, and ochratoxin. The lab utilizes polymerase chain reaction (PRC) analysis to identify and quantify mycotoxins in air samples. Samples are collected in 37mm cassettes, preloaded with 0.45 um pore-sized filters, and sampling times are  longer than typical sporetrap grab samples. Whereas the above referenced types of lab analysis rely on a lab technician’s ability to visually identify and count… PCR has over a 95% confidence rate and is more automated.

Mold Testing – How to Interpret Lab Results and Air Quality Data?

So you’ve had an inspection and received the lab results… what does it all mean? Companies that just send convoluted lab reports without further explanation should be put out of business. It is the role of the Certified Indoor Environmental Professional to help interpret the lab results in combination with what was gleaned from the visual inspection.

Sporetrap lab results should include, at the VERY minimum, one outdoor sample and a handful of indoor samples. The outdoor sample is used as a control to compare to the indoor samples. Because there can be such variation in sporetrap samples the statistical significance from collecting so few samples is very limited. Most labs simply share a chart showing how many of which type of genera were present.

Mold Testing Air Quality

Sporetrap Chart – Mold Testing Non-Viable, Non-Culturable

Some labs offer their own “limited interpretation,” such as the MoldScore from EMLab P&K. “MoldSCORE™ is a specialized method for examining air sampling data. It is a score between 100 and 300, with 100 indicating a greater likelihood that the airborne indoor spores originated from the outside, and 300 indicating a greater likelihood that they originated from an inside source…” Below you can see some obvious “spikes” that EMLab identified as statistically significant higher counts of Cladosporium and Pen/Asp indoors compared to outdoors.

Mold Testing Air Quality

Mold Testing Lab Interpretation

Some Building Biologists refer back to the Healthy Home Standard for guidance on interpreting sporetrap results:

Mold Testing Air Quality

Building Biology Sporetrap Interpretation Method

Viable (Culturable) results are usually presented in CFU’s, and different labs use different set points to determine low, medium or high probability of significant mold growth. Building Biologists often refer to the Healthy Home Standard suggested interpretation guidelines:

Mold Testing Air Quality

Building Biology Viable Culturable Lab Interpretation

There is much less standardization for interpreting these last two sample types. MVOC results may come with lab interpretation such as this: “Levels below 8 ng/L are typical for most homes and should not cause great concern for healthy individuals. Levels between 8 and 30 ng/L indicate a low level of mold which, generally, affects people who are sensitive to molds. Levels above 150 ng/L indicate that a high level of active mold growth is present and it is likely that nearly all occupants of the home will be affected.”

Mold Testing Air Quality

Microbial VOC (MVOC) Lab Analysis

Mycotoxin results may be paired with an individual’s blood test results, if they are working with an environmental doctor. We are often called in as a result of an environmental medicine practitioner finding that an individual’s body is reacting to mycotoxins… and then we have to find where that exposure is occurring – usually at home or work.

1) Decide if environmental sampling would add value to the case, 2) define a sampling plan that would answer a question or prove/disprove a hypothesis, 3) perform testing in accordance with industry guidelines, 4) only use qualified laboratories with good track records and the appropriate certifications, 5) interpret data in combination with information collected during the inspection, 6) provide the interpretation in a user-friendly manner written to the “right audience.”

Until mold testing becomes more regulated it will remain “an art and a science.”

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101 Responses to “Mold Testing – Air Quality Lab Interpretation”

  1. Alex Stadtner says :

    It’s impossible to know without seeing the building and gathering more data. The decision to open the wall and search for mold is ultimately up to professional discretion… so mold investigations are a bit of science AND art. It sounds like you made the best decision at the time with the information you had. Now if symptoms and evidence of exposure persist… you might want to circle back. We would not have recommended “mold inhibiting paint,” but that, too, is a professional judgement call. In general physical removal of mold growth, mold spores and mycotoxins is preferred over using biocides which may come with their own set of unintended consequences.

  2. M Lark says :

    I had a mold inspection done recently and the Spore Trap Analysis shows extremely high scores of Penicillium/Aspergillus behind the wall of one bedroom, much higher than the count outside. The air inside that bedroom was also higher than in other rooms, but not as high as outside. There had been a leak in that room, but the moisture level was fine when tested by multiple people and there was no visible mold. The company advised not opening the wall, though they said if we did and found mold we should call them back. Instead, we repainted with mold inhibitor paint. Now I am wondering if that was the right thing to do. The occupant of the room has been very ill and tested positive for Ochratoxin A from penicillium and aspergillus. Should we have removed the section of drywall where the leak was or would that have made things worse by releasing mold spores into the room?

  3. Alex Stadtner says :

    We’d have to see the report in order to comment. If a mold inspection or mold testing only covers a kitchen and bathroom, than generally the report would only address the areas tested. In other words, how would the industrial hygienist (mold inspector) know about the rest of the building if they only assessed a smaller subset? Let us know if we can be of service.
    Healthy Building Science

  4. Felicia Demont says :

    Hello, We recently found visible black mold under a bathroom vanity. That area has been cleaned free of mold. We last summer went 4 weeks without a/c working – more possibilities of mold growing.The inspectors report came back with specifically tested Kitchen and Bathroom for the test results. I’ve been told that meant the entire building is safe. Wouldn’t the report specifically indicate entire building? We have 11 offices, 3 bathrooms, 2 conference rooms and a reception area.


  5. Alex Stadtner says :

    Given moisture and food and proper temperatures – all found in a wet residential wall cavity – microbial growth may begin forming within 24-48 hours. The only way to know for sure would be destructive testing of the wall or somehow peaking and mold testing within the wall cavity. 10 days of wet drywall is a recipe for microbial growth.

  6. Mary says :

    On March 2, 2018 the roof of my coop apartment broke up because we had high winds of 50-60mph. Water was rushing down the perimeter of my bathroom walls onto my bathroom floor. You can hear the water (like Niagara Falls) running down my bathroom and bedroom walls, my bathroom and closet walls, and my bathroom and kitchen walls. The water came through my wall shelf in the bathroom. This water came down from 6:30pm – at least 9:00 pm and still sporadically the next day. The next day and the day after roofers came and redid the roof. 10 days later a company came to dry out the walls in my bathroom, bedroom, and closet., They punctures holes in my bedroom walls and closet, took off the ceiling in my bathroom and used machines with tubes to dry the walls. The fact that this happened 10 days later can mold and mildew be behind the walls? Will Air Quality Test pick mold and mildew between the walls? I want to know if anything could affect my health. Please would like a response as soon as possible. Thank you.

  7. Alex says :

    Hi Erica Adams. Based on what you wrote, it sounds like your house has a mold problem. I have experience with mold. Eventually mold spores wears down the immune system to the point that it can no longer defend itself and body reacts i.e. throat, stomach, walking, burning sensation on skin, weakness, acid reflux, burping, breathing etc. Multiple systems become involved with mold illness. Do not look for the mold or disturb it, if you find it. I disturbed it and within 15 minutes I could not breath for 6 months. Have a qualified mold company search for the mold and remediate it as soon as you can. You will save yourself and family from an illness that is difficult to treat and thousands of dollars in the long run. Please listen to this advice.

  8. David Sasse says :

    Respectfully, as a policy we do not comment on sampling and lab results that we did not collect ourselves. There is no way I can tell if the samples were collected properly and without the context of visual observations, I cannot interpret lab results and provide any accurate analysis.

  9. Philip harway says :

    I’m having a hard time finding any analysis of Scopulariopsis mold. My test came back as
    Raw Count 4, 27 spores/m3 and 8% of total. We are told that this requires action because they are a concern to occupants.
    What I have found seemed to indicate that this is not that much out of range, although outside air and other areas tested found nothing. HELP!

  10. Erica Adams says :

    We purchased a house 6 months ago and a couple months after moving in a started experiencing pins & needles in my feet and hands. I headed to the doctor for blood work and nothing. I had a company come in an preform air quality testing. It came back with high levels of smutts on all 3 levels. The control take outside was much lower ( normal) than inside the home. The company did say that this was rare to see. We went ahead and had them put those air cleaner machines in our home for 48 hrs. They performed another air test a week later and said the levels were normal. What can cause high levels of smutts inside a home? I felt better for a bit and now that it’s winter time and we are in the house more symptoms seems to be returning. I also have two young children. Any advice ?

  11. […] Most experts, including the EPA and California Department of Public Health, suggest only testing under very specific conditions. In general, a moisture and mold inspection by a qualified professional is far more useful in determining if a mold problem exists. However, there are some circumstances that warrant additional air quality testing.” Read more here… […]

  12. Alex Stadtner says :

    Assuming these were air samples, it is entirely possible that spore counts are significantly lower when the home is unoccupied. Human actions such as walking, breathing, opening doors and windows, sitting down, making the bed, etc. – all aerosolize fine particulates indoors – including mold spores. Spores themselves are microscopic and will eventually settle out of the air and rest on horizontal surfaces such as rugs, beds, floors, door trim, counters, etc. If nobody is indoors moving around the airborne spore counts may appear much lower than when the home was occupied – even if no remediation has occurred. Mold testing, in the absence of a thorough mold inspection, is relatively meaningless.

  13. Lauren says :


    We have had mould testing performed in the house that came back at a range of 12000 for aspergillosis and have been told that there have been microtoxins picked up in the samples also. There were also high levels of other moulds found. After the family all becoming ill with headaches, blood noses, chest infections, kidney infections, coughs and conjunctivitis we have moved out. These tests were performed 8 weeks ago. I requested that the samples be taken again and the same company are now saying the levels have dropped to 800. Is this possible without any remediation or ventilation to the property?

  14. Alex Stadtner says :

    Not clear how the samples were collected. Air or bulk dust? Not sure of conditions or other clues within the structure, or how the building is designed with regard to air breaks and ventilation, etc. Too many unknowns to give meaningful suggestions. I would suggest, however, that you have a good, independent 3rd party mold inspection company perform an inspection and make professional recommendations.

    IF these were air samples – and IF they were done correctly and not in an agitated room – then these results are higher than average and may be an indication of a hidden reserve of mold spores indoors. But there are too many unknown variables to tell you anything more.

    Mold remediation companies are regional so without knowing where you are we also cannot suggest any remediators.

    Good luck

  15. Angie says :

    Mold testing came back with:
    aspergillus over counts of 600,000 spores per m in bathroom
    aspergillus over counts of 450,000 spores per m in a closet

    Thoughts on whether it has spread to the AC ducts? the rest of the house? Thoughts on what a remediation company would want to demo to get rid of the mold?

    These counts seem unreasonably high… any insight would be appreciated as we are looking to purchase the home…

  16. Alex Stadtner says :

    Your concern sounds completely reasonable. I’d suggest you get a local industrial hygienist or Building Biologist(R) to assess the building. You need an independent, third party to come and assess the situation and document whatever they find. You may need a good paper trail down the road. Keep good notes and hire a local pro to explore the home and perform their own mold testing. Best of luck. Hopefully your symptoms subside and you don’t find anything too alarming in discovery.

  17. Michael Philips says :

    I need some advice on how/what to test. We had a mold removal company come based on some findings from a plumber of a water leak in the bathroom. The tech (who was new) didn’t see the mold and tried to dry out the wall using an air mover that was blowing air into the area. After a day, the supervisor came and saw there was mold. They went in and did a full mold abatement and after the job was completed they ran an air quality test that came back clear of mold. My family has had respiratory problems a couple days after the blower was removed. We are raising a complaint to the mold company, and don’t want to rely solely on their tests. What kinds of tests should we run independently to see if there is mold in our home? My concern is that they blew mold spores all over our house when they tried to dry out the area. Thanks for any advice you can give! Thanks.

  18. David Sasse says :

    It is really impossible to interpret lab results without an accompanying visual inspection.
    Merely the presence of mold spores without context does not tell your their source, severity or health implications.
    See this statement from the California Department of Health Services:

    As a policy, HBS cannot interpret lab results we did not ourselves collect.
    We recommend not only testing but a full Mold and Moisture inspection or even better a full healthy home pre-purchase inspection prior to purchasing any property.

    David Sasse
    Director of Environmental Services
    Healthy Building Science

  19. Brian Simpson says :

    I recently had a mold air quality test on a house we were looking to purchase and the test results came back as having ascospores, aspergills/penicillium, basidiospores, cerebella/monodictys, cladosporium, smuts/myxomycetes, and stachybotrys. The total raw count 53, count/m3 707 in the basement and raw count 40 count m3 was 533. Are these numbers dangerous?

    I have a 2 year old and we are thinking about having more children and the fact that the house has mold is a little unnerving especially stachybotrys (raw count 2, count/m3 27 and %4).

  20. Anna Levis says :

    Mold is never a good thing. Spores reproducing on counters, walls, and wood trim can take flight and aggravate allergies and respiratory ailments, as well as ruin drywall, carpet, and woodwork. But in every life a little mold will form, and not every patch is a reason to panic.

  21. Sheryl says :

    I strongly suspect a serious black mold problem in my apartment (a rental). I bought a reusable pump for testing the air from My Mold Detective because I think that, in addition to the mold I can see in the old bathroom and skylight vents, there may be significant mold in the walls and ceiling due to plumbing and roof leaks. I’m on the top floor of an old brownstone built in 1852. Cleaning the mold out of the vents may not be enough to solve my problem. It may be necessary to use anti-mold paint to encapsulate what’s in the walls and ceiling.

    I live in a rent-stabilized apartment in NYC, and I pay so little in rent that the building manager generally ignores me and I generally don’t bother him, but I’m getting sick from something in this apartment – very likely black mold – and he can’t ignore this. I’m gathering information about the scope of the problem before contacting the building manager.

    I have two questions about taking the air samples:

    1) OUTDOOR SAMPLE – The instructions for taking an outside sample (3-4 feet off the ground, 10 feet from buildings) does not make sense for someone living on an upper floor in an urban setting. “Outside air” for me is not 3-4 feet off the ground. Since I’m on the top floor, a sample taken outside the window or on the roof would seem more relevant. Also, I’d have to go blocks away to a park to be where there wasn’t a building within 10’. And if I did that, I couldn’t take an indoor sample within 15 minutes of the outdoor sample (not to mention, there are no outlets in public parks). And how relevant is an outdoor sample taken blocks away, anyway? See my problem with the instructions? The outside air relevant to my apartment is what comes in through my window. I’d like to take the sample outside my window, on the fire escape (which is the only outside surface to set the pump on). It will be within 10’ of my building, but everywhere is within 10’ of a building around here. Does this make sense to you? Or should I buy a super-long extension cord and take a sample on the roof? If that would be better, why would it be better?

    2) INDOOR SAMPLE – I keep my window open almost all the time to mitigate the symptoms I am experiencing which I believe are from black mold (migraines, coughing, difficulty breathing, constant runny nose). I feel a lot better when the window is open – or when I’m not home at all. For how long do the windows in my apartment need to be closed before I do the indoor air test?

    Thank you for any guidance you can give me.

  22. David Sasse says :

    It is really impossible to draw any conclusions on sampling data without the context of a visual inspection. It is our policy at HBS not to comment on lab results collected by other parties, as we cannot guarantee that the samples were collected in a consistent way that meets our high standards. I am not sure how, where or under what conditions your sampling was performed. You also do not seem to have any outdoor samples to be used as a control comparison. I can speak generally that sampling results alone are insufficient to determine the status of a building. I would refer you this document by the California Department of Public Health,
    I would also recommend a full mold and moisture inspection with more comprehensive sampling.

  23. Bill Brown says :

    I recently had an air quality test done fore mold spores that came back as highly elevated with 301 CFUs for Penicillium and 18 for Curvularia. I have friends who stay with me on a semi-regular basis who have asthma and one who is immune compromised. Should I be concerned about these levels? And, if so, can anything be done to minimize the issue?

  24. Alex Stadtner says :

    Based on a) no obvious evidence of water damage or visible mold growth, and b) no reported history of water damage or mold, and c) a couple spore traps with low levels of anything… You probably don’t have anything to worry about. That is contingent on there have been a very thorough mold and moisture inspection that didn’t reveal visible signs or odors of microbial growth. In general, a few spore trap results could find low levels of many different types of mold spores. These could have come in through a window or on the clothes of you or the inspector. So a few spores in the absence of any visible signs or other clues of water damage or mold growth is not that concerning at face value.

  25. Anthony says :

    Hi, in the process of purchasing a home. We had a mold inspection done for peace of mind.
    Outside sample was taken as well as under the sink. Inspector said under the sink did not look
    bad, but saw some water stains. Results came back with low levels of chaetomium. Sellers don’t want
    to touch and refuse to “fix” anything, say remodel was done less than 1 year ago. Really like the home,
    should I be concerned with results? Your recommendation?

  26. Jim says :

    Hi, I just recently had my air tested today and realized after the fact that I had a HEPA filter running continuously before it was tested. The filter was only shut off for an hour before testing. Do you think I should retest if the test results come back negative? The filter is a Honeywell 50250 AHAM certified for use in rooms up to 390 square feet. It was in a 400 sf living room that I had tested and is connected to by open doorways to three other rooms I tested.
    If I retest how long should the filter be off to get a good result. Also should the windows be open or closed during the day of testing?

  27. Sophia says :

    Sorry to hear about your water damage and mold losses. Moving is a bear anyway, and to worry about all your contents containing residual mold is not fun.
    You’re incorrect that Stachy won’t show up in air samples, but that’s another story.
    ERMI would tell you if any of the 36 species of spores evaluated are present on the couch. It won’t tell you how they got there or if they are present in more abundance than all your other contents or the new place.
    There are a number of ways to test the exterior of the couch using bulk sampling techniques such as tape-lifts, swabs, bulk sample of fabric, etc.
    If you’re hoping insurance or anyone else will pay for the cleaning you’ll have to have an independent, 3rd party mold inspector collect the mold samples and analyze the results.
    Contents are very expensive to “clean,” so unless the couch is worth a lot of money you may opt to just let it go.
    Best of luck,

  28. Jess G says :

    Cross-contamination question:

    We moved out of a moldy place but have our stuff. What test, if any, will help us see if our possessions have mold spores on them? We had our insurance send someone out for an air test. However, since Stachy won’t show up in the air…what is my best test choice? I know ERMI takes dust samples but I want to test things like my bed (can’t “dust” that) or my couch.

    Thank you so much!

  29. Deborah says :

    We bought our home in Dec of 2015. The home inspection stated the home had no signs of mold in the crawl space or attic. We gutted the house and completely remodeled it between March 2015 and October 2015, moving into the home at the end of October. In November of 2015 we had the crawl space encapsulated. Since the encapsulation mold has been found growing throughout the crawl space which was discovered when we installed a crawl space dehumidifier in July 2016. We had a free crawl space evaluation from a CleanSpace company and they said the encapsulation wasn’t done properly – three large holes were found open leading to the outside of the house and several holes around plumbing, septic, etc were left open to the living space above. Since moving in we both have developed signs of mold exposure. I was tested and found to be positive for both mold exposure and mold sensitivity. We did an ERMI dust test for mold in the master bedroom which was positive (6) and we had MoldTestUSA inspect and again the results were positive. MoldTestUSA found the same molds to be present in the crawl space that the ERMI test found present in the master bedroom. The master bedroom has a readily detectable musty odor. MoldTestUSA found Aspergillus|Penicillium, Cladosporium, Myxomycetes|Smuts and Torula in high concentration (1001+) in the crawl space. The highest on the ERMI test were Aspergillus niger (47), Aspergillus penicillioides (520), Aspergillus restrictus (71), Aspergillus sydowii (13), Aspergillus versicolor (160), Aureobasidium pullulans (83), Cladosporium sphaerospermum (20), Eurotium (Asp.) amstelodami (83), Penicillium corylophilum (25), Penicillium variabil (58) and Wallemia sebi (73). We contacted a mold remediation company who required us to go through their recommended hygienist for an evaluation prior to remediation. The hygienist found elevated particle levels at the 1.0, 2.5, 5.0 and 10.0 micron range in the master bedroom at the air return and the TV room. It was discovered during the evaluation that the air return in the master bedroom was actually open to the crawl space below due to a hole cut into the space of the panned air joist left behind from the old HVAC system. The remediation recommended by the hygienist only addressed the crawl space. Nothing was recommended for the living space other than replacing the hardwood floors that are badly cupped and cleaning the HVAC ducts and changing the air filters to HEPA ones. The master bedroom and den have carpeting. Shouldn’t the carpet and padding be replaced in those rooms too as part of the remediation? Obviously are primary concerns are health related and it seems like the mold exposure in the living space is being largely ignored. We know the master bedroom in particular definitely has mold. What would you recommend we do as a next step to make sure the living space is restored to a healthy environment and the remediation is both comprehensive and successful? Thanks!

  30. Sophia says :


    Yes. This is very common. One must rely first and foremost on a good inspection. If an inspector smells a musty smell it should be a surefire clue that there’s a problem. Don’t let the absence of testing data deter you from finding the moisture problem. Generally a musty smell only exists where there is active microbial growth around a current moisture problem. So don’t give up until you find and fix it. There is probably active microbial growth as a result of an active leak somewhere in the building.

    Why mold testing might not detect a real source of indoor mold?

    It sounds like your inspector used spore trap testing to look for airborne mold spores, and it sounds like they may have only used a couple sample locations and times.

    1) The outdoor conditions may have had unusually high counts. Perhaps a neighbor was leaf blowing, or the sample was collected near a leaf or compost pile, or the wind was blowing more than usual.

    2) The indoor conditions may not have resulted in the aerosolization of mold spores. Spore trap testing requires spores to be airborne. Some spores are heavy and sticky, and unless there is active contact and/or air flows, it’s quite possible that an obvious source of mold indoors won’t show up on a spore trap. Some technicians will collect a sample before and after “agitating” the room. Sometimes they shake curtains, fluff pillows, etc. I’ve even known one consultant to use a leaf blower indoors! I don’t suggest the latter. But the point is that there could be settled mold spores or active cultures that simply didn’t have airborne spores during the testing.

    3) Testing locations may not have found where the source of mold exists. What you smell is microbial volatile organic compounds (MVOCs). What you smell are gasses released from active microbial growth. A metabolic byproduct of eating that stinks. (Sound familiar?) Gases can travel through air/vapor permeable materials much more easily than particulates. The type of testing your mold inspector used only looks at particulates. You’re smelling gasses. There are tests to evaluate MVOCs. And somewhere – testing location matters – in your building you probably would find elevated mold spore (particulate) counts. It may be in a well, floor, attic or crawlspace. But based on your description I’d be surprised if a thorough and well-trained mold inspector can’t find a current leak.

    So there are many reasons you may have a problem that isn’t detected by just a few spore trap samples.

    Bottom line – trust your nose and eyes and don’t put all your eggs in the “air testing basket.”


  31. David Sasse says :

    We as a policy do not comment on sampling results that we did not perform ourselves. The reason is that we cannot know the conditions for the sampling and if the samples were actually collected and handled according to our high standards. It is next to impossible for us to interpret or comment on results without the content of the accompanying visual inspection. I would recommend contacting whomever performed this sampling to answer your questions.
    Generically, these air sampling results look like spore trap results where a sample volume of air is run through a spore trap and the particulates are captured onto a microscope slide. The lab looks at the slide visually and identifies the species listed. The raw count is the actual number of spores observed on the slide and the spores per cubic meter are an extrapolation based on the raw count and the volume of air that passed through the spore trap. – David
    P.S. Stachybotrys is colloquially known as “Toxic Black Mold” and any staychybotrys observed is generally considered a concern.

  32. michelle says :

    I’m hoping someone can tell me what these numbers mean ? Samples were done by a air quality test…….Cladosprorium spores per m3 – 4,500 raw count112
    Other Basidiousspores-spores per m3 80, raw count -2
    Pen\asper -spores per m3 -1,600. raw count 40
    Stachybotrys-spores per m3 -34,000 raw count 840
    Total spores per m3,- 40,180.. raw count 994

    Also what exactly is a “raw count “

  33. Kate Pendergrast says :

    What might explain a definite mold smell throughout a house where a mold test came back “negative” (lower than outdoors and 0 count for marker molds)? There is no question in my mind the odor in the house (and subsequently on my clothes) was mold. What gives?

  34. Alex Stadtner says :

    Sorry to hear your kids are suffering from exposure to mold.
    600 to 16,000 sounds like a significant spike in indoor mold spores. It may be an indicator of a source of mold spores indoors.
    There can be a lot of fluctuation in mold spore traps. It is common for there to be big swings, which is why a good company will suggest performing as many spore traps as the budget will endure.
    Doing just one outside sample is common practice in residential mold inspections, but doing only one sample outside doesn’t allow the inspector any leeway for the variation that is so common. It’s good to collect outdoor control samples before and after testing indoors (sometimes wind conditions change), as well as on different sides of the building (watering, compost bins, trees, etc.). 16K indoors is unusually high. It could be the result of user error, or it could have been accurate at that given moment. Same with the outside sample. 600 spores per meter outside is rather low. It could be user error (ran sample too quickly, didn’t connect trap to pipe well), analyst error (wrong count at lab), or it could have been reality at that place at that time. Testing cannot substitute for a thorough visual inspection – sometimes requiring destructive investigative techniques. But if you’re trying to use testing as a way to determine which course of action to take… we’d suggest either a) lots more testing, or 2) a more close visual assessment to determine the necessary scope of work.
    Good luck,

  35. Lauren says :

    Hello- We recently found out that our daughters are very allergic to mold and they have had declining health this year. We had air quality testing completed in our home and found high levels of Pen/Asp. The highest concentration was 16,000sp/m3 and the outdoor control was 600. The inspector figured out water was coming from a leak in the chimney-we didn’t have an visual signs. We also figured out the the person who did our insulation covered our soffets. We had the chimney removed, the roof patched and a vent put in the roof. The mold removal company suggested a costly and extensive removal process. We decided to have air quality testing done again since the source of the water stopped and the pen/asp levels were zero outdoors and under 200 in each level of our home. Now we are really confused as to what to do. The second inspector was very new to air quality testing (I believe we were his first) so I wonder if it was user error. Is it normal for levels to fluctuate like this? Should we get a third air test? Should we proceed with the work as planned since the mold was high at one time and our girls are getting sick?

  36. Alex Stadtner says :

    In general experts recommend removing any porous (easily damaged and difficult to clean) materials, such as drywall and carpet, 2 feet from any visible signs of water damage or mold growth. So if their are water damaged or mold affected materials behind the cabinets it would be best practice (“industry standard”) to remove them before considering the mitigation complete. We would need more information to make an informed mold remediation protocol for your home, but it is very common for inspectors/mediators to recommend too much work. If the home is vacant and the damage was limited to a kitchen, than I would assume a good, thorough cleaning from a regular cleaning company would suffice – assuming the kitchen mold remediation occurs under containment and is fully mitigated according to industry standards. The ducts could also be cleaned prior to occupancy. It depends on many variables, but it is rare that the entire home needs to be scrubbed by the mold remediation crew wearing white suits, etc. You are wise to try and strike a balance between precaution and practicality. Finding that balance isn’t always easy!

  37. Robert says :

    Alex, I am purchasing a home and found Stachybotrys under a kitchen sink. I understand the cabinetry needs to come out to see how wide spread this mold is. The owner of the house is refusing to do anything beyond repairing a leak under the sink and cleaning the visible area. I know more needs to be done under the sink.

    My question is regarding the Penicillium / Aspergillus levels found in the air samples we had taken. On one side of the house, there are levels of 124 raw/ 1653 spore/m3 (vs. exterior 12/160) and on the other side of the house the levels are 12/133. My inspector is calling for a full house remediation to wipe down the walls, scrub the air and clean the air ducts on both sides of the house and 2 A/C systems.

    I want my family to be safe, but I don’t want to hold firm on a full house remediation if its overkill. I would appreciate any thoughts or advise you could provide.

  38. Alex Stadtner says :

    Without seeing the situation it’s hard to give a solid opinion.
    However, in general, if particle board or plywood is severely water damaged it must be removed as part of the restoration.
    If you can afford expert mold remediation I’d also suggest you hire the best remediator you can find.
    Good luck,
    Healthy Building Science

  39. Lori says :

    We had an air quality test done on

    In our kitchen after finding a built In enclosed 9 ft shelving that had severe moisture damaged, beyond wood rot the scores were indoor sample cladosporium raw count 1 spores/m3 53
    penicillin/ aspergillus types raw count 3 spores/m3 160
    Ascospores raw count 2 spores/m3 110
    Basidiospores raw count 19 spores/m3 1,000
    With us contacting him back with o my receiving this paper, he said just shop vac out, could where a little mask if wanted from hardware store, fill in with some 2 by 4’s or 4by 4’s and just seal back up. This seems very odd to me? Please note we have someone In house with compromised immune system, would appreciate your advice as soon as you can. Thanks

    types raw count 3 spore

  40. […] present but not aerosolized and therefore,underreported if only air sampling is performed..” ( This is exactly why our air sample test showed what it […]

  41. Sonia says :


    We had a mold inspector come out and he said there might be a potential of mold growth hidden in our inside affected walls. The weep screed was covered and the sprinklers were spraying onto the outside walls. The air samples results in my daughter’s room:

    All results came back lower than the outdoor sample except these 2:

    raw count = 1 (outdoor sample 0)
    Spores/m3 = 40 (outdoor sample 0)

    Raw count = 1 (outdoor sample 0)
    spores/m3 = 40 (outdoor sample 0)

    The inspector recommended removing walls and a full remediation which is going to be expensive out of pocket. I had a second mold inspector come out last week and he didn’t notice anymore moisture on the affected walls and said that these air sample results are very low. What are your thoughts??

  42. Alex Stadtner says :

    Hello Homeowner,
    Congrats on the new place. Bummer about the water damage and potential mold growth.
    Without seeing more of the results and knowing the conditions under which the samples were collected, and without a visual assessment, we cannot say anything with any authority on this particular water damage case. And we’re not doctors or toxicologists – so we cannot really say if the space is “safe for your child.”
    But with those caveats I would tell you that it is unusual to find Stachybotrys in air samples, and the spore counts that you reference do appear significantly higher than what is generally seen when there isn’t interior (long-term) water damage. Stachy does like to grow in very wet conditions over long-periods of time. So the conditions you’ve explained – with a leak for over a year – are conducive for supporting some of the more problematic indoor molds such as Stachybotrys.
    In any mold remediation job the contractors should follow best practices for water damage restoration (IICRC S500) and mold remediation (IICRCS520).
    If you have any doubts about how their handling the remediation you should hire a third-party industrial hygienists – like us!
    Good luck,

  43. Whitney says :

    We moved into a brand new home in January of 2015. A week ago, we noticed some water damage – it turns out there was an issue with our master bathroom shower liner installation and we have had an undetected water issue for 14+ months. We had air samples and swab samples taken. The air samples came back this morning with the following results:

    Aspergillis 2500 count/m3
    Stachybotrys 272000 count/m3

    I have a 9 month old infant in the house and the stachybotrys count seems extremely high to me. Is it safe for her to be in the house? The builder will be coordinating the demolition and remediation.

  44. Alex Stadtner says :

    Sorry to hear you’re suffering symptoms in your building at work. There is a very high cost for businesses that operate in sick buildings, because folks like yourself might not be as productive (“presenteeism” or miss more work (absenteeism). I’m not saying that your symptoms are definitely caused by the building, but it is a common story.

    Elevated mold spores indoors, or an internal source of mold spores and mycotoxins, may contribute toward your symptoms. But that is a medical question, not a question for Industrial Hygienists.

    In general a raw count of 1 spore is very, very low and not very statistically significant. More important is that an inspector saw visible clues of microbial growth (mold growth) in the ducts. If true, that could be a serious problem and should be addressed ASAP. It would need to be professionally remediated and your IH would probably suggest the duct cleaning by NADCA standards after the mold remediation.

    In closing, I trust the visible inspection and confirmation of mold growing in ducts as the single most significant indicator there’s a problem. If you can see it already – the only reason to collect mold samples would be to determine what type of mold is growing. If you can see the mold – air sampling would only be recommended in very few cases. If you can see mold growing indoors there is a problem that needs to be addressed. (period)

    Best of luck.

  45. ali says :

    i have been suffering from sinusitis and allergic rhinitis for 2years now and never had issues before. recently my job heat broke and duct guy came in and said we have bad moisture problem and mold in duct work. they did air quality test at work and alternaria came back slightyly elevated raw cfount 1, count/m3 7 and total was 50% and said could cause allergy in individuals is this something i should be concerned about and ? this is what could be causing my problems. Could an elevated amount of mold spores cause sinus issues. Thanks

  46. Rachel B says :

    We just had our house tested for mold due to major health concerns of our 1 year old son. This is what it came back as and we are still currently in our home. Should we move immediately due to the levels of toxic mold?
    Client Project Identification
    outdoors Livingroom Bedroom
    raw ct. Cts/m3 % Area raw ct. Cts/m3 % Area raw ct. Cts/m3 % Area raw ct. Cts/m3 % Area


    Arthrinium 1670 22261 74% 60 800 17%

    Ascospores 468 6238 86% 201 2679 9% 210 2799 58%


    Basidiospores 30 400 6% 9 120 0.4% 18 240 5%


    Chaetomium 12 160 1% 9 120 2%

    Cladosporium 18 240 3% 24 320 1% 24 320 7%




    Fragments 2 27 0% 6 80 0.3% 6 80 2%


    Penicillium/Aspergillus* 6 80 1% 252 3359 11% 21 280 6%

    Pollen 20 267 4%


    Scopulariopsis 6 80 0.3%


    Stachybotrys 72 960 3% 15 200 4%





    Total Spores (Cts/m3): 544 7,252 2,252 30,019 363 4,839

    Sample Volume (Liters) 75 75 75

    Sample Time Minutes: 5 5 5

    Background Debris** Moderate Abundant Many

    *The spores of Penicillium/Aspergillus cannot be differentiated by non-viable sampling methods.

    **Fibers, skin fragments and dust are indicated by few, moderate, many, and abundant.


    410901 Outdoor Air 410902 Living Room Air 410903 Rear Bedroom Air

  47. Chintan Sanghani says :

    Thanks for your feedback. There will be no occupants during the testing. Also, our plan is to close the windows and seal off the HVAC vents. We also plan to inoculate the complaint rooms using harvested spores (different species) from the lab and keep them suspended in air using fans. We intend to introduce these spores 24 hours prior to starting the mold machine. I would like to understand the typical life cycle of mold spores. How will these inoculated spores reproduce? I think this will play a factor in determining the start time of the machine and collecting subsequent samples. What are your thoughts?

  48. Alex Stadtner says :

    This sounds like a suitable testing protocol for an air purification device.
    The largest uncontrolled variable will be occupants, and doors and windows being opened.
    But with that many samples you should be able to demonstrate if your mold removal device works or not.
    Sounds interesting. We’d be happy to collect the mold samples if you need a 3rd party mold inspector for the experiment.
    Best of luck,

  49. Alex Stadtner says :

    Sounds like a tough predicament. The results you sent didn’t come through very well, and we wouldn’t be able to give you a solid answer regardless of these results.
    Firstly we don’t know how these results were collected, under what conditions, etc. We don’t know what the building was like prior to the sewage leak, nor do we know what the microbial environment was outside. There is no “baseline” from which to compare results. But perhaps most importantly we would have to see the site, walk around with meters and gadgets, and really get a feel for the extent of the damage – if any. Without a professional mold inspection we really cannot comment on these results or tell you the scope of necessary remediation. I strongly suggest you hire an industrial hygienist you can trust.
    Best of luck,

  50. Chintan Sanghani says :

    Hi Alex,

    This webpage and your comments to the questions posted above appear to be very informative. I am currently working on a mold sentry machine prototype testing. The machine design claims to reduce indoor mold spore levels within a house / office set-up. In order to verify this claim, we have developed a customized test protocol and I would like to obtain your feedback on the same. Provided below is our project scope:
    Conduct independent lab testing to evaulate the efficacy of Mold Sentry Unit. Air Samples (both cultural and non-cultural) will be collected and analyzed as per the test protocol listed below:
    Test Protocol Include the following: (Test protocol is a custom testing developed by us.)
    1) Air Sampling Types: Cultural and Non-Cultural
    2) Test Site Location: Office Building with 5 Rooms
    3) Sampling Locations: Complaint Room 1, Complaint Room 2, Control sample – Non Complaint Room, and Outdoors (both the complaint rooms will be inoculated with different types of mold spores; non-complaint room – no inoculation) – All rooms will be treated with the machine.
    4) Number of Samples: Two each of each sampling type from each location.
    5) Sampling Period (7): Pre-Release, Pre-Start, 24 Hrs After Machine Start, 48 Hrs After Machine Start, 72 Hrs After Machine Start,  96 Hrs After Machine Start, 120 Hrs After Machine Start
    6) Total Number of Samples: 112 (56 – Cultural and 56 – Non-Cultural)
    7) Test Duration – 7 days
    The scope of the project also extends to pre-test test site preparation and survey.

    Looking forward to your reply.

  51. Lauren says :

    Hello, desperately need your help. There was a 5 hour toilet overflow on top floor of house. Afterwards we let the entire residential building dry out. However, after a few days the tenant was concerned about mold. So I had a mold test done. I just bought the house 2 years ago, and had a full mold inspection, and passed with flying colors. So how am I to read this test I had last week. The Mold Company that did the test wants to do the remediation by tearing up the entire ceiling and walls on the second floor of my tenants apartment, to the tune of $5,000 dollars. please help! I desperately need a second opinion on the results on the mold test. Any help would be greatly appreciated. I don’t know what to make of the test, or what to done next. See mold test results below.

    Lab Sample Number:
    Client Sample ID:
    Volume (L):
    Sample Location
    Upstairs Unit Kitchen
    Spore Types Raw Count Count/m³ % of Total Raw Count Count/m³ % of Total – – –
    Alternaria – – – – – – – – –
    Ascospores 1 40 2.4 11 460 32.2 – – –
    Aspergillus/Penicillium 31 1300 79.3 5 200 14 – – –
    Basidiospores 3 100 6.1 15 630 44.1 – – –
    Bipolaris++ – – – – – – – – –
    Chaetomium – – – – – – – – –
    Cladosporium 4 200 12.2 1 40 2.8 – – –
    Curvularia – – – – – – – – –
    Epicoccum – – – – – – – – –
    Fusarium – – – – – – – – –
    Ganoderma – – – – – – – – –
    Myxomycetes++ – – – 3 100 7 – – –
    Pithomyces – – – – – – – – –
    Rust – – – – – – – – –
    Scopulariopsis – – – – – – – – –
    Stachybotrys – – – – – – – – –
    Torula – – – – – – – – –
    Ulocladium – – – – – – – – –
    Unidentifiable Spores – – – – – – – – –
    Zygomycetes – – – – – – – – –
    Total Fungi 39 1640 100 35 1430 100

    Analyt. Sensitivity 600x – 42 – – 42 – – – –
    Analyt. Sensitivity 300x – 13* – – 13* – – – –
    Skin Fragments (1-4) – 1 – – 1 – – – –
    Fibrous Particulate (1-4) – 1 – – 1 – – – –
    Background (1-5) – 1 – – 1 –

  52. Alex Stadtner says :

    Hi Maryam,
    Without having taken the samples and seen the mold remediation area, it’s impossible for us to give this clearance testing a pass or fail.
    If the Master Bedroom was fully remediated and that sample was taken inside containment – any Stachy would be a fail in my book. But we didn’t write your Mold Remediation Protocol so I don’t know what your Industrial Hygienist will say. Our clearance testing protocol would also fail a contained area if mold spore counts were higher inside containment than outside. Using our precautionary guidelines that would be an instant fail, unless there were other extenuating circumstances. HEPA vacuuming and running scrubbers is a good start. Wet-wiping is another approach, and many mold remediation companies will alternate between wet-wiping and HEPA vacuuming.
    But having said all that – the naked eye is a pretty good too for indicating if an area is “clean” or not. Inside containment you should be able to run your gloved finger across every horizontal surface (including the remediation equipment) and not see any dust on your finger. If you can do that in your Master Bedroom – it’s probably pretty darn good – but I cannot pass or fail a mold clearance we haven’t seen.
    Good luck,

  53. Maryam Jamshidi says :

    Hi Alex
    Mold report from EMLab P & K in my master bedroom is as follow:
    Spore trap analysis shows Stachybotrys 2 raw count 27 per m3.
    Also Indicator mold score assessment shows 159 where 300 is the highest.
    Indicator exposure level is 40 spores/m3 while outside sample is <13.
    The company who did the test mentions thatThe results show that Chaetomium and Stachybotrys marker spore types, as well as Hyphal fragments, were found to be present in the sample collected from the Master Bedroom while the same spore types and hyphal fragments were not found in the outdoor sample. This indicates that the master bedroom requires further cleaning in the form of HEPA Vacuuming to remove all settled dust/spores from all surface (walls, exposed wall framing, ceilings, and floors) prior to rebuild.
    I would like to know if the score mentioned above is high enough to take further actions to remove mold before rebuilding the wall? If yes, would HEPA vacuuming take care of the problem so that the retest after vacuuming give me the confidence to rebuild the wall.
    Thanks in advance

  54. Alex Stadtner says :

    Hello Angie,

    Ask the company who did the testing for more information. Hopefully they did a thorough mold and moisture inspection so the results can be interpreted in context. Simply giving the results of a couple sporetraps is insufficient information for an expert to draw any conclusion.

    I can say that we usually do not find airborne Stachybotrys indoors. It’s a relatively heavy and sticky spore, and usually only grows where there has been long-term (>2 weeks) moisture exposure. Stachy is the most infamous of molds, but one spore certainly isn’t enough to raise an alarm if there were no other clues of water damage or mold growth. Under the right conditions some species of Stachybotrys does create a mycotoxin (trichothecene) that is particularly virulent. It may warrant additional investigation, but by itself I wouldn’t panic about your results.

    Best of luck,

  55. AB Hoffman says :

    Looking for help interpreting our indoor air quality test results. There were 1- Raw Count, 20 Count/m3 and 1.4% of total of Stachybotrys found in one of our bedrooms. Should this be a concern? There are other leves like Aspergillus/Peniccillium – 46- Raw Count, 970 Count/m3 and 67.5% of total. Finally 1-Raw Count, 40 Count/m3, and 2.8% of total for Chaetomium. Should any of these counts be a concern? There are more on the test, including Rust of 1 raw/20 count/m3 and 1.4% of total.

    Thanks so much,

  56. Alex Stadtner says :

    It would require a more thorough assessment to provide any real conclusion. There were not enough data points to make the “air quality tests” very meaningful. It also appears that they only looked at airborne mold spores, which is a very small sliver of all the IAQ parameters that could be tested. Carpet in a basement is always a bad idea, but it could be easy as removing the carpet. They may be some hidden, larger problems relating to water, but a good inspection should reveal clues about water damage and mold growth. Your experience of being given a lab report without any further explanation is all too common in North America. It’s why some companies can offer a mold inspection for so cheap – their inspectors need minimal training and their reporting is non-existent. You get what you pay for. Find a local Building Biologist up there and see if you don’t get more bang for your buck.
    Best of luck,

  57. Terence says :

    My wife and I have put an offer in for a house in the Montreal area. I requested two pre-purchase inspections (building inspection and air quality test). We had no suspicion as a reason to order the air quality test, but we just wanted to make sure. Since it is a pre-purchase inspection, the test had to be non-invasive.

    We received the air quality tests back Friday evening (and I had to let the agent know by Friday if we were taking the house). The test has numbers on it, and three line items are highlighted in red, however no further explanation is given. Therefore I have no context in which to take the results. I don’t know if the results are a bit high, moderately high, very high, or extreme.

    The building inspection did not reveal any particular problems with the house that would alert us. The house was built in 1973, and the previous occupants were very dirty people. There is carpet everywhere, including an area rug directly on the floor in the basement. The house has three bathrooms, one of which was recently redone. The other two bathrooms, the kitchen, and the flooring are all going to be completely redone. The HVAC system and chimney will also be professionally cleaned.

    Are you able to take a look at the results and give me some understanding of what they mean ? I can certainly pay you for your time.

    Penicillium / Aspergillis – Basement 1771 spores/m3 – Outdoor 27 spores/m3
    Markers (Stachbotrys, Chaetomium, Globossum) – Basement 914 spores/m3 – Outdoor 0 spores/m3
    Other Spores – (Ascospore, Fragments, Arthrinium, Other Dark Brown) – 1600 spores/m3 – Outdoor 0 spores/m3

    Cladosporium / Basidiospores / Alternaria – these were all measured at 0 spores/m3 indoor

    I got an extension from the real estate agent until Monday. We are due to meet her Monday morning at 10:30. The period given when you pre-purchase inspections is simply not enough to investigate air quality issues.

  58. Alex Stadtner says :

    Thanks for writing in. Please review the comments below this blog. Your inquiry about whether or not to remediate based on 2 spore trap samples is very similar to previous comments, and my answer would also be very similar.
    We don’t have enough data to make a professional recommendation on your mold situation.
    -Alex & Healthy Building Science

  59. PS says :

    Hi Alex,

    I just received my mold report back with the following results for Aspergillus/Penicillium:

    Living Room:
    125 Raw/1667 Count/90%

    42 Raw/560 Count/20%

    Should I be concerned/remediate at these levels?


  60. Alex Stadtner says :

    The extent of contamination can only be determined through an investigation. The investigation will be visible in nature, but may also include additional sampling to determine what areas are Condition 1, Condition 2, or Condition 3. This blog about the 3 C’s explains what these classifications are for mold investigations.

    Regarding what to do about mold contaminated “contents,” I suggest checking out this blog about how to clean up mold. It’s not complete, but it will give you an idea about what materials can be salvaged. In general hard-surface items can rather easily be cleaned and remediated, but soft or “porous” surfaces often have to be tossed. There are some companies that will clean contents, but it’s often cost prohibitive for items like books, furniture, clothing, bedding. I suggest you talk this over with the Healthy Building Inspector while they’re on site.

    It’s good you’re getting some medical support, too. They often will also weigh in on whether or not to keep some items.

    I’m sorry you’re going through this. It aint easy. But with good help you will pull through and eventually this will be just a memory in your rearview mirror.

    Until then, hang in there.


  61. Karen says :

    Hi Alex – I took your advice and scheduled an appointment with your firm to do an in-depth evaluation. In the meantime, I got results back yesterday from Pro-Lab for a swab/petri dish sample of extensive dust I got off a recently installed bedroom fan. It came back showing Chaetomium, Cladosporium, and Rhizopus/mucor. The Heater has been going pretty consistently over the last month, and I am really concerned that we have been breathing these airborne spores. I’ve been the most sensitive with respiratory symptoms, and have a medical appointment scheduled regarding a probable sinus infection. We are looking at completely moving out of the house until we can have this remediated, but I wanted your advice on whether everything is contaminated and needs to be left. Can washing clothes/sundries and packing them out in sealed bags be an option?

  62. Alex Stadtner says :


    Thanks for writing in. In general I like what the mold inspector had to say. It’s actually surprisingly close to what anyone from Healthy Building Science would have said with regard to your lab results. Granted the number of samples collected is very small, but in-and-of-themselves the results you reported are not alarming.

    Relative humidity (RH) levels between 50-60% are actually ideal, so I would be happy with those levels. If, however, you find significantly elevated RH in the crawlspace, attic, or wall cavities, that could be an indication of a hidden moisture intrusion problem. I’d be curious what RH you read in the crawlspace.

    Do pay attention your symptoms. You’re wise to notice any ill effects and pay attention to the building and weather. Seek professional medical advice if you experience symptoms and have medical questions. An environmental doctor may be able to isolate what you’re responding to, which makes the job of the environmental inspector that much easier.

    Would love to give the place a better look-over and see if there was any residual mold left over from previously reported water events. You could do more invasive (destructive) exploration and/or testing around the areas with a known history of water damage. Removing the floor trim or opening a hole in the drywall around the reported sewer overflow could be illuminating.

    Lastly, don’t hedge all your bets on mold. There may be other airborne allergens, toxics, and irritants within the home. A good environmental doctor might help you understand the cause… if inspectors cannot find the source.

    Best of luck. Our more senior inspector has an airplane and is always looking for an excuse to fly. And another of our inspectors is always driving north to visit family in OR. We’d be happy to perform a more comprehensive inspection and testing program if given the opportunity.


  63. Karen says :

    Alex – We recently moved into a 1958 house in a rural NorCal area. The building inspection noted a prior roof leak in the garage around the chimney, with white mildew on several of the planks (new roof in 2009, but don’t know if leak occurred then). There was a disclosure of a septic backup in the ground level family room that resides on a concrete slab (no vapor barrier) adjacent to garage. There is also a significant open crack in the garage floor (no vapor barrier, rebar), that was not considered, by the building inspector, as a structural issue to the living space. There are areas where paint on some of the original redwood siding was peeling/blistering, but that was chalked up to poor paint prep and landscape watering hitting the siding.

    After moving in during the summer, I felt that the house was slightly humid (no A/C). Once the weather changed, I noticed that some of the windows would condense if the blinds were completely closed. A hygrometer has shown that the house never gets below 50% even when I get rooms to 70*, and outside temp is below 40*. North facing master bedroom/bathroom stays quite cool even though there is new Hardy plank siding. The meter has gotten as high as 60% in this location.

    I just had a moisture/mold inspector evaluate with moisture meter, non-viable air fungal analysis, visual inspection of indoor area and crawl space (which showed prior evidence of standing water). He neither saw nor smelled anything of mold concern, and the area around the chimney currently showed dry.

    Report from analysis is (raw,S/m3):

    Alternaria – 2, 27
    Ascospores – 7, 220
    Basidiospores – 527, 17,000
    Cladosporium – 63, 2000
    Epicoccum – 1, 13
    Hyphal Fragments – 5, 160
    Penicillium/Aspergillus – 4, 130
    Rusts/smuts/myxomycetes – 9, 120
    Ulocladium – 4, 53
    Particulate density – minor

    Family room:
    Alternaria – 5, 67
    Ascospores – 2, 64
    Basidiospores – 19, 610
    Cladosporium – 40, 1300
    Epicoccum – 2, 27
    Hyphal Fragments – 20, 640
    Penicillium/Aspergillus – 6, 190
    Rusts/smuts/myxomycetes – 8, 110
    Ulocladium – 1, 13
    Particulate density – major

    Master bedroom:
    Alternaria – ND
    Ascospores – 2, 64
    Basidiospores – 13, 420
    Cladosporium – 29, 930
    Epicoccum – ND
    Hyphal Fragments – 14, 450
    Penicillium/Aspergillus – 4, 130
    Rusts/smuts/myxomycetes – 2, 27
    Ulocladium – 3, 40
    Particulate density – major

    I asked about the significant indoor increase in Hyphal Fragments, and the response was: “Hyphal fragments are noted when the analyst observes fragment of mold parts in the sample. It is perfectly normal to have some hyphal fragments in a sample both indoors and outdoors. The difference in the counts for the indoor and outdoor hyphae count is not statistically significant. In the absence of other factors, such as, visible growth or evidence of active water intrusion, the difference becomes even more insignificant. Conversely, if we observed active water intrusion, high levels of spores, a moldy odor, the fragment count would add to the pile of data suggesting an indoor source for spore development. In this case, none of those are true and the counts are considered normal background levels.”

    I have been having shortness of breath and coughing, which prompted me to do more research about complications related to previous water intrusion into homes. It is possible that the rural air is causing the respiratory issues, but considering the house history, a lot of red flags are going off. Especially since we have not gotten significant rain yet.

  64. Alex Stadtner says :

    Hello J Watts,

    If it were only that easy. You need to start with a professional mold inspection where a trained inspector can offer his professional opinion. Your results appear to be from one sporetrap test, which is extremely limited and almost meaningless without at least one outdoor sample with which to compare.

    You do have some genera of mold that could potentially be toxigenic, but the quantities are somewhat irrelevant without outdoor comparisons.

    If you’re nervous and want answers, you’ll need to get a pro involved. And with pros, you get what you pay for. Not sure who would have just taken one sample and not helped explain to you next steps.

    Good luck,

  65. Jeffrey Watts says :

    It is difficult to know what test results pose a serious threat to the health of my family – as in “do we just have this cleaned” or “do we need to move out NOW!”

    Today I received Test results with the following elevated:
    Chaetomium Raw Count 1240 Spores per m3 17000
    Cladosporium Spores 14500
    Penicillium/Aspergillus Raw Count 8920 Spores 120000

    Can you please enlighten me on what health risks may be?

    Thank You
    J. Watts

  66. David Eckstein says :

    Thanks for the quick response
    They did take an outside air sample and samples in the homes living spaces .The results were
    Outside Control
    Raw Count/Spores per m3
    Other Aescropores 16/110
    Other Basidospores 8/53
    Peniscilliujm/Aspergillus 8/53

    Total 32/216

    Then the bathroom area, which sits under the attic area where the leak occurred
    Raw Count/Spores per m3
    Peniscilliujm/Aspergillus 8/53
    Smuts, Myxomycetes 4/27
    Stachybotrys 40/270

    Total 52/350
    There is no visible mold in the bathroom nor is there any odor. We were told that while that bathroom is not really bad with a 270 stachybotyrs reading at 270, it makes the attic reading seem ridiculously high at 29,000, it is elevated because it reflects molds not in the control sample.

    As for the old area, the 10 to 20SF is water damaged the mold, is scattered over this area in pattern, it is not a solid black sheet but a blotchy/patchy pattern.

    There are no vents in roof, but ridge beam appears to have a vent.

  67. Alex Stadtner says :

    Sounds like a fairly typical scenario. You were wise to address the source of the moisture problem first. There may indeed be reason to revisit the water damaged areas and have it professionally remediated. A couple comments and follow up questions before giving my opinion.

    Sporetrap (airborne, non-viable) mold testing has it’s limitations. Without an exterior baseline sample the results are rather meaningless. Also, only having one sporetrap sample is very limiting in terms of statistical certainty of results. Regardless of the potential for mold, industry best practices (IICRC) would suggest removing any water damaged, porous materials (e.g., drywall, some insulation), and to extend 2 feet past the last visible sign of water damaged materials. This can lead to scope creep, however, and if the drywall does not appear damaged from the underside and doesn’t show visible signs of mold growth above… I might be inclined to leave sections of the drywall in place. That’s a judgement call. Best practice would be to pull it if there’s visible signs of water damage.

    1) In my opinion 10-20 SF of visible mold growth would be significant. However, if it’s just visible water stains over that area and only visible mold growth in a lesser area… I’d be much less concerned. When you say 10-20 square feet, are you talking about water stains or visible mold growth? If it’s the latter you’ve got a significant issue that needs professional remediation – no matter what species of mold it is.

    2) Is the attic ventilated? Are there little screens on your soffit or can you see a ridge vent? If it’s ventilated with outside air, sporetrap testing is rather meaningless.


  68. David Eckstein says :

    I had an air conditioner in my attic on which the condensation pipe got clogged and the water collector tray overflowed soaking my drywall below. This was in Sept 2014. We fixed the problem and let it dry out. A contractor went into my attic in July 2015 and said that when the drywall was wet it had molded significantly enough that and I should have it checked even though the mold and drywall was now dry as the water source had been repaired months before. There was no odor or mustiness The area which was infected was between 10/SF and 20/SF. On the advice of the contractor I had it checked. The mold readings came back showing the following:

    Raw Count/Spores per m3
    Chaetomium 24/160
    Ciadosporium 8/53
    Penicillum/Aspergillus 1,632/11,000
    Pithomyces 4/27
    Rusts 4/27
    Stachybotrys 4,368/29,000

    Total Spores 6,040/40,267

    How severe are the Penicillum and Stachybotrys numbers? They seem extraordinarily high for such a small area which hasn’t been wet for a very long time. The Mold Air Quality company is recommending a very elaborate remediation program which in part entails removing ALL the insulation in my attic and tearing out my entire bathroom ceiling. I have been putting this off. The CDC on-line says this could be cleaned with bleach. Are these numbers as bad as they appear? Could these be bogus numbers, Do they make sense for the size and scenario described? Any input would be appreciated.

  69. Alex Stadtner says :

    Would need to perform a moisture and mold inspection in order to comment on results. Too bad the folks who did the testing didn’t stick around to help interpret the lab results. That’s where Healthy Building Science stands apart from the competition. At least this is true in the residential market. When a commercial operation hires an industrial hygienist they’re usually competent enough to help interpret results. Unfortunately, in the residential sector it’s every person for themselves and too often the customer is left holding a bill and results they don’t understand.

  70. Morgan says :

    I had a mold test done and cannot understand the results. when it says (TNTC) to numerous to count is that bad. also is 4587 air spore count in my bedroom bad. All high counts were determined to be Aspergillius/Penicillium.

  71. Alex Stadtner says :

    Hi Michael,

    Mold Lab Results:
    Tough to say without an inspection, but if we got this sort of result back and didn’t see any significant visual signs of water damage… we’d probably suspect that the outside control sample was a dud. If you’d had windows open and the outside sample just so happened to be low… it’s entirely possible the majority of the spores found inside came from outside and just don’t show up on the lab results. I’d have a cleaning service carefully clean up any visible signs of mildew (mold) around windows from minor condensation, run your air filters and keep the windows closed, and have a retest. Don’t vacuum or sweep or do anything too disruptive before the testing. Ask for at least two outdoor samples and try running them in a different location than the first round. Have one collected before the indoor samples are taken, and another after. Often times, this simple double-test method will reveal a different story. Honestly, without running a whole bunch of sporetraps the statistical significance is rather low… which is all the more reason to follow my next piece of advice…

    Fogging with enzymes:
    WOW! Do not proceed. The number one goal of mold remediation is the physical removal of mold spores (careful cleaning and air scrubbing). “Mold remediation” = “How to clean up mold?”

    Fogging will only add something new to your house. It does zero to clean or remove the spores that triggered this alarm already. All the experts say only to use a biocide or chemical cleaner as a last resort. I’d certainly not do any fogging.

    First hire another company to do the retesting and request a few extra sporetraps. If that round comes back “positive,” than perhaps you need a more thorough mold and moisture inspection to identify where the spores are coming from.

    Good luck!

  72. Michael G says :

    Hey Alex,

    I stumbled across your article digging for information about mold testing. Wonderful site and article! If it’s okay I would like to ask for your informed opinion. I’m in the middle of selling my house and the buyers just completed a mold air test with their inspection company, which came back somewhat elevated. First, the outside control, which came back with Cladosporium 680/m3 & 102 raw count and Penicillium/Aspergillus at 170/m3 & 26 raw count. They also tested the kitchen, which came back with Cladosporium at 28,800/m3 & 4200 raw count and Penicillium/Aspergillus at 800/m3 & 120 raw count. Then they also tested the master, which came back with Cladosporium 2,800/m3 & 420 raw count and Penicillium/Aspergillus at 930/m3 & 139 raw count.

    This shocked me as I’m pretty allergic to mold and having no major symptoms. We did just have nearly 2 weeks of soaking rain and mid-70 temperatures here. It felt nice out so during that time we often left windows in the master and downstairs open, with the A/C off. This was literally days before the inspection and subsequent mold test that they surprised us with. Had I thought about it beforehand I would have kept the house buttoned up and the A/C blasting with good allergen filters in both air handlers, but I did not.

    As the result of this the buyers called in a green home specialist who proceeded to look around at surfaces (especially near previously opened windows), pointing out minor surface mold. I mentioned to him that the windows had been open for hours a day, literally for almost a week and the AC off. He didn’t bother to look for any other possible sources (under sinks, etc). On his way out he measured relative humidity in the kitchen at around 55%. He came back with a quote of $2500 to fog with enzyme and scrub the air that the buyers are now trying to stick us with.

    As of now I’m keeping the house at 72 degrees and running the fans in both AC units 24/7 with allergen filters installed. I also just got a large dehumidifier that I’m running to try it out as much as possible. I’m also considering getting a second opinion as I really felt like the guy was 100% salesman when he was here.

    Please let me know what you think…



  73. Alex Stadtner says :

    I’m sorry to hear about your cats and illnesses.
    The Penicillium and Aspergillus spore counts you mention are higher than I’ve ever seen. I would consider that alarming. But I don’t know how the samples were collected, or how much air was collected, etc. So I cannot say with any certainty what those relatively high counts mean. The Chaetomium, too, is concerning. You need a good inspection to confirm or deny the presence of an indoor source of mold. Is there a leak somewhere? An old leaky roof, busted pipe, leak under a sink? Are there site drainage issues? Is there a crawlspace or basement, and have those areas been fully inspected? You need someone with the right training and tools to perform a professional mold and moisture inspection.
    Best of luck,

  74. Evelyn says :

    Hello, I am grateful to find this article, at the same time concerned with what I am reading. I live on the beach, and have lived in this one bed room condo for almost 7 years now, and not only have I lost two cats here ( renal failure & Cancer) .. My mother & I have been feeling very sick. I have been experiencing panic attacks, headaches, and have landed in the ER twice, once for hospitalization for my symthoms. They gave me benzos, and none helped me much. I did research and decided to call in a mold testing inspector. The results returned back, and all he mentioned were they were very high in mold, my bedroom had Raw count of aspergillus / penicillium of 25,920 and count/m3 of 172,800 .. Those numbers were alarming. In the closet where I once had a leak but since repaired it, was also tested, and came back with aspergillus/penicillium of raw count of 9,600 and count /Cm3 147, 840 or chaetomium 4,400 Raw count and Count/ Cm3 67,760 … Can you tell me what I’m up against? I have 3 cats and I am worried about all of us, along with my belongings, cause I am reading how people end up moving out and leaving all their things behind. Please help. Thank you, God bless.

  75. Alex Stadtner says :


    What did the Industrial Hygienist (IH) or Mold Inspector tell you?

    The mold inspection is what you should really be paying attention to, not these limited lab results. In the absence of a detailed inspection these lab results are rather meaningless.

    However, if these results were all we had to go on, the elevated Stachybotrys and Chaetominum counts are probably statistically significant enough to justify a closer look at previously water damaged or existing wet areas. Not sure why the lab didn’t distinguish between these two distinctive genera of mold. Might be a long-term leak and some wet drywall somewhere. Should show up in a good moisture and mold inspection report. If this were me, I’d get a second opinion in the form of a thorough inspection and possibly another round of mold testing.

    Good luck making this enormous decision – you don’t want to buy a mold problem you cannot afford to fix. So be careful, trust the experts, and trust your gut.

  76. CMG says :

    We received a report where the overall mold source assessment was 300 with an overall exposure level of 1,509 spores/m3 and raw ct 80 inside at location and 1,387 spores/m3 and raw ct 26 outside. We are looking to purchase this house and remodel the kitchen. Should I be concerned…even without the remodel?
    Penicillum/Aspergillus types = 100 Indicator Exposure Level @ location spores/m3 = 53 – raw ct = 1 – outside 110/2
    Cladosporium species spores = 100 Indicator Exposure Level @ location spores/m3 = 160 – raw ct = 1 = outside 960/18
    Basidospores = 100 Indicator Exposure Level @ location < 13 – raw ct = 0 – outside <13/0
    "Marker" Spore types (Stachybotrys/Chaetominum) = 300 Indicator Exposure Level @ location 920 – raw ct = 69 – outside <13/0
    "Other" spore types (Alternaria/Trichocladium) = 150 Indicator Exposure Level @ location 323 – raw ct – 6 – outside were same numbers.

  77. Alex Stadtner says :

    Hello Rebecca,

    If two out of three residents experience those symptoms in your place, and the symptoms go away or improve when you’re away from the unit and return when you reenter the unit, I’d suggest you vacate the space until you figure out what’s going on. Those symptoms sound rather serious and if two adults are suffering … it might not be a healthy environment for any occupants… but especially concerning is the infant.

    Every mold inspection company is different. We usually turn mold results and reports around within a week, and charge a slight premium if folks want the results expedited. Since we didn’t perform the mold inspection at your place I cannot say when you’ll receive the results. A week should be plenty of time unless they did cultureable or viable sampling that will require the lab to grow mold on a petri dish over time. Call the inspection company and they should give you an ETA.

    You can search our mold blogs by clicking this link.

    Best of luck,

  78. rebecca says :

    how long does it take to get mold results back we live in a basement apt and had a mold inspector in on friday and did tests but im fearfull of the results i always have a melaticy taste in my mouth disyness confusion and times aches and pains etc… my bf is experencing similar symptoms with a lung infections we have a 4 year old that fortuanly isnt experiencing symptoms just wondering how long it takes for the results to come in because honestly i dont no how much longer we can live in this we would leave but we have nowhere to go

  79. Alex Stadtner says :

    Thanks, JS.
    While we cannot make recommendations for your building without performing a mold inspection, the visible indication of mold growth in the basement is enough to know that 1) there was (or is) a moisture problem in the basement, and 2) there needs to be some form of mold remediation. The Pen/Asp count of >6000 is most likely significant, as it’s more than we generally find in both indoor and outdoor samples, but without knowing the conditions of the building during the sampling or the outdoor baseline Pen/Asp count… the interpretation must stop there. We have written a blog about what to do if you have mold in a home, and how to clean up mold, but these are only intended for small areas of mold and not for the DIY Mold Remediation of a significant mold problem. If you’re considering getting rid of furniture I suspect it’s a larger problem and that you’re already experiencing symptoms. If that is the case, get an Industrial Hygienist (IH) involved so they can help you define the scope of work and rules of engagement for the mold remediators. There are protocols for carefully cleaning furniture and porous belongings, but this method of remediation is up to the discretion of the owner and IH. The IH can also perform a post-remediation clearance inspection to verify the job was done right and fully cleaned – BEFORE the contractors take down containment. The key to mold remediation is thorough cleaning and physical removal of the mold while not cross-contaminating other areas of the building. Don’t let anyone sell you into using biocides or other toxic chemicals to “kill the mold.” It’s all about removal and careful cleaning.
    Best of luck,

  80. JS says :

    Great article! I’m trying to get a better understanding of all this mold “stuff”. We had a pen/asper result come in at 6420 spores/m3 inside with 0 spores/m3 outside. Visible mold in basement. This was a spore test report. Would this be enough for remediation/tossing “plush” furniture, etc? My understanding is that the outdoor sample should be higher than indoor…if indoor is higher, it’s a greater issue? Is that correct?

  81. Alex Stadtner says :

    Hello Jen,

    The answer to your question is an unequivocal YES. Not only is it possible, but it happens more often than not.

    If I understand correctly, your doctor has demonstrated that your body is currently reacting to Stachy but your air samples haven’t detected any Stachy. There are several possible reasons.

    1) You may be exposed to Stachy in other locations. Office, outside, friend’s house, doctors office!?!?

    2) Wherever you collected your samples indoors, may not be where the Stachy resides.

    3) You may be reacting to MVOCs from Stachy, not spores. Your testing most likely is only looking for spores and fragments. If the Stachy is in a wall/floor/roof and unable to share spores in your living space, it doesn’t mean that when it’s wet it cannot send gases (microbial VOCs) into your living space. Stachybotrys is one of those particularly virulent molds that cause harm via spore or MVOC.

    4) Stachy is a “sticky and heavy spore.” So unless you’ve recently disturbed it, it’s unlikely to be found in air samples.

    It’s unusual to find Stachy in air samples. Settled dust, or tape lifts or swabs, are generally more effective methods of finding Stachybotrys indoors.

    IMHO, if you’re suffering symptoms and your doctor says it’s because of mold exposure, it’s time to call in a pro and stop doing home air test kits. Even the CA Dept of Public Health says mold testing is a bad idea. I’d suggest a trained professional who is a Certified Microbial Investigator visit your home and determine the best course of action.

    Best of luck, and be safe!

  82. Jen says :

    Hello .. My question is , Is it possible to have your home air tested through air sampling and have high levels of some molds yet not show Stochybotrys? I am under the care of an environmental physician and My labs show positive testing for Aspergillus alterum Chlodasporium and Stochybotrys . The Stochybotrys is the only one not showing on the mold air sampling.. Could you clarify please .. Thank you

  83. Alex Stadtner says :

    Healthy Building Science does top-notch professional mold inspections and mold testing throughout the San Fransisco Bay Area, and beyond. Happy to talk shop if you still need mold testing in San Jose. We always suggest starting with a mold and moisture inspection first, because sometimes mold testing is a bad idea.

  84. AK says :

    Finding a reliable local company to handle mold testing in San Jose is a much more difficult task than expected.

  85. Alex Stadtner says :

    Hello CG,
    Not enough information provided to give you a good answer about your mold lab results interpretation. In general, “too much” mold/yeast indoors would be defined in relation to an outdoor or other control sample. Not sure why you’re using plates.
    Best of luck,

  86. Cgriffith says :

    I do air plate testing using the 3M petrifilm plates. Can you tell me what would be an excessive amount of yeast or mold count on one plate? We are reviewing our maximum thresholds and wondering if our threshold is correct.

    Thank you for your help!

  87. Alex Stadtner says :

    Would need to know if you’re talking about viable (cultured) or non-viable (spore trap) mold sampling? Also need to know if you’re numbers are in CFUs, spores/m3, or raw counts on a slide? Were samples taken outside as a baseline? There’s not enough information in the note you provided to give any professional advice. The types of mold you identified are ubiquitous and therefore don’t raise a red flag by themselves. Good luck.

  88. stacy says :

    i had mold air sample done and two samples of mold seen it came back withascospores at 107 , basidiospores at 320 , cladosporium at 213 and pen/asp grop at 320 my kids hve been very sick with breathing problems since we moved back in or home after a pipe broke and we had water damage so we just had these test done are these levels something to worry about?

  89. Alex Stadtner says :


    There are strict and standardized testing procedures for biological testing in food prep and food packaging facilities. Often it is required an independent 3rd party inspector provide mold and yeast testing services.

    Call or give more details and we can try and help. Where is the project? How big? What operations are occurring? Is an agency involved and mandating the air quality testing? Have they mandated any surface sampling? Have they mandated specific test methodologies.

    It’s unlikely that placing out petri dishes and self-testing for mold will suffice.

    Best of luck,
    Healthy Building Science

  90. Mohammad Farrukh says :

    we are running a food industry and we are facing microbial contamination primarily of yeast and mold. can I test air samples for molds by simply placing the PDA petri dish in air for 5 to 10 minutes?

  91. Alex Stadtner says :

    Hello Andrea,

    It is entirely possible, although very difficult and unusual. Mold spores are very small and invisible to the naked eye (“microscopic”). Because they are so small they are easily disturbed from surfaces and maid airborne (“aerosolized”). Cleaning efforts usually involve wet-wiping and HEPA vacuuming, because these methods minimize aerosolization and are able to capture most of the tiny mold spores.

    But even using best practices there are usually some mold spores found in air or bulk (tape or swab) samples collected during a mold clearance inspection. It’s how many that should determine a pass or fail. If there were none found on your job – consider it a success! But if you can run a white glove anywhere in containment and see visible dust… and the results come back with zero mold spores… odds are the testing produced a false negative and you should retest. A visual examination and the “white glove test” usually tell the whole story.


  92. Andrea says :

    Is it possible to have zero mold spores after remediation?

  93. Alex Stadtner says :

    Thanks! Mold testing and interpreting lab results remain a top concern for our clients, and we routinely see less scrupulous “all-in-one” companies either waste money on unnecessary tests, or use the results to wrongly justify remediation beyond what would be necessary. We like being independent third-party “mold testers” for that very reason. There’s no conflict of interest. Glad you enjoyed the post. We should do one on PCR and ERMI soon… or mycotoxins… lots of questions about that recently. Thanks, Alex

  94. Lee Blanchard says :

    Great post.Really looking forward to read more. Awesome.

  95. Alex Stadtner says :

    Here is a link to a video highlighting some of the limitations to using DIY settling plates for testing mold.

  96. Alex Stadtner says :

    Due to the variables you mentioned (weather, dry, traffic patterns, leaf blowing, etc.) we would not recommend petri dish testing. And doing so in isolation (e.g., only doing one and not doing similar samples indoors) would tell you very little about the living space. I presume you’re most interested in the indoor air quality? Whatever the case, the settling plates outside will tell you very little. This sampling method is vary rarely used by professional industrial hygienists.

  97. Shawm c says :

    How do you properly Petri dish test outdoor ir quality of an apartment building what’s the best place to put the dish and for how long? What type of weather is best testing time, right after a good rain when it’s dry at day or night? Living in maryland

  98. Shawm c says :

    How do you properly Petri dish test outdoor ir quality of an apartment building what’s the best place to put the dish and for how long? What type of weather is best right after a good rain when it’s dry at day or night? Living in maryland

  99. Alex Stadtner says :

    Cool. We can consult on an hourly basis to review and discuss your lab results. As all the experts say, lab results without a professional inspection only tell a very small part of the story… but nonetheless they can help support a hypothesis. Call Healthy Building Science for IAQ and consulting.

  100. Belinda Davis says :

    I have air test results that I would like someone to look at and talk to me about.

  101. Jhake Turner says :

    In case you’re in uncertainty of any disagreeable development in your house, you ought to basically accept there is an issue at whatever point you see shape or scent mold smells. Testing ought to never take the spot of visual assessment (which is prescribed) and it ought to never use up assets that are required to redress dampness issues and evacuate unmistakable development.
    Individuals used to feel that forms were innocuous yet it isn’t. The truth of the matter is, a few molds process a poison called aflatoxin (poisonous and around the most cancer-causing substances known) that causes disease and demise in individuals.
    At times, mold development is shrouded and troublesome or hard to place and find. In such cases, deliberately led testing and visual investigation may help focus the area of tainting. Nonetheless, form testing is once in a while advantageous for attempting to answer inquiries or request about wellbeing concerns. For additional data, see mold testing services

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