How mold air tests are done

Before diving into how to read your results, it’s helpful to understand how air tests sampling is done and how they capture the different mold spores present in your home.

An air test uses a sealed cassette, which is attached to an air sampling machine. At Claro, we use Zefon Air-O-Cell cassettes, as pictured below.

Each cassette can only be used once and must remain sealed before and after use to avoid cross-contamination between tests. They are supplied by a lab, and once the sample is collected, it’s sent back to the lab where it is examined under a microscope to identify the type—or types—of mold present in your home.

After unsealing the cassette, it’s attached to an air sampling machine, which draws a raw count of mold spores across its surface over a specific sampling period. The sampling machine—something that looks a bit like it came out of Ghostbusters—runs for 5 minutes exactly, pulling in exactly 75 liters of air and capturing any mold spores present:

It’s important to note how small the air sample actually is. By design, the machine draws in a limited volume of air, then extrapolates the results to estimate mold spores per cubic meter (m3). Because of this, false negatives are common.

To get the most accurate results, all air purifiers should be turned off several hours before the test. At Claro, we often use compressed air to stir up dust and fungal matter, helping get mold spores into the air. If there’s visible mold or water damage, it’s usually a good idea to hit that area with compressed air to encourage sporing. Alternatively, you can use a swab test to sample the mold directly.

We also take an outdoor air sample to compare against indoor levels. In humid or damp climates, outdoor mold spore counts tend to be naturally high—so if windows were open recently, your indoor results could look elevated even if there’s no issue.

Once the indoor and outdoor samples are collected, the cassettes are sealed and sent to a lab, where technicians examine them under a microscope to identify the mold types present.

Note that the lab isn't going to be able to tell you what mycotoxins are present. They will just tell you the types of mold like stachybotrys,  penicillium aspergillus or cladosporium.

Typical lab turnaround time is around three days, but it may take longer if they’re culturing the sample. 

Cultured vs non-cultured tests

For air tests there are two main types of tests, cultured and non-cultured tests. At Claro we typically only use cultured tests (where the lab tries to grow the mold and fungal matter from the sample) after we complete mold remediation because after our treatment the spores will still be there, but they are dead and can't reproduce. The cultured test (via-cell from our lab) tells you this.  

Pairing with a professional mold inspection

‍We talk about this in more detail on our mold testing page, but ideally, the person testing your indoor air quality is also a licensed mold inspector. One of the most reliable mold tests is the trained eye of an experienced professional.

A good inspector knows where to look for hidden water damage, how to test drywall and insulation for moisture, and when musty odors or visible mold are signs of a bigger issue.

They’ll also check overlooked areas like under your kitchen sink, inside closets, or in your basement—places mold loves to hide.

Don’t hesitate to ask whoever does your mold inspection for their gut feel on how serious the mold issue is. Their experience often tells them more than the test results alone.

Reading mold test results

Understanding at home mold tests

Most at-home mold tests we’ve seen—like this highly reviewed one from Amazon—simply culture mold on a plate. When you look at the plate, the results can either be alarmingly full of mold or give you a sense of comfort.
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The problem is, the environment isn’t controlled for sample size or compared to your outdoor mold levels. So while these tests can be a decent starting point for sampling fungal matter in your home, they won’t tell you if you have a specific type of mold like Stachybotrys, and they can’t tell you how much mold is present.
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Understanding professional mold test results

When done properly, professional air sample tests will identify the types of mold in your home and the concentration per cubic meter. These are critical pieces of information when deciding whether or not to move forward with mold remediation or cleanup.

That said, mold test results can be confusing—even with a professional. The reports often feel like they’re written in another language.

This section is meant to help you make sense of your results so you can better understand the mold types and meter cubed spore levels listed. We’ll focus mostly on the reports we use here at Claro, but we’ve included examples from other labs too. Our samples are tested and processed by Eurofins Built Environment Testing in Chantilly, VA.

Keep in mind, different labs may format their reports a bit differently, but most will include a table listing the mold types, their respective counts and estimated load in m3. Below, you’ll see examples from Eurofins and also from AssuredBio in Oak Ridge, TN.

‍Note: This information is for guidance only and should not replace the advice of a qualified mold professional.
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A guide to reading tabular mold test results
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This is the most common type of test result you'll get back from the lab that your mold testing professional uses. Below we've labeled each section so you can start to comprehend what you are looking at.
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A - Test and lab identification
B - Raw counts of spores taken in your test sample
C - The labs estimate for the full mold load in your home based on calculations they do to extrapolate your sample to a larger space m3 = meters cubed
D - Non-mold elements found when sampling