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Understanding Lab Reports

Air samples

On each lab report, you should see a chart with several columns, plus a notation of where the sample was taken. The report gives you:

NOTE: The lab may label “spores per cubic meter” as “CFUs/m3”. CFU stands for “colony forming unit,” which is another way of saying “spore”.

So, let’s look at one theoretical report:

Location: Living room Raw count Count/cubic meter
Aspergillus/Penicillium-like 70700

In plain English, this tells us that 70 little round spores of Aspergillus, Penicillium, or other mold producing little round spores was counted on the surface of the sticky tape in the spore trap air testing canister, along with 20 spores of Cladosporium. If the final count for a full cubic meter of sampled air is 700, then the inspector must have sampled 1/10 of a cubic meter.

What’s the safe number? There are no governmental standards for what is acceptable. Further, what level is acceptable for your health may not be acceptable for my health. From my experience, the average room that doesn’t have a mold issue might show zero or one or two Aspergillus/Penicillium spores in a lab report.

If I saw 70 spores counted, I’d figure something was going on, and it would be my job to figure out where the mold growth is. I would know that it had to be someplace that was open to room air, because hidden mold in a wall cavity doesn’t show up in a spore trap test. If I saw even seven spores reported, I’d still suspect that there’s some mold growth somewhere. Seven isn’t a high number, but it’s higher than one or two.

See how easy this is? You look for the elevated numbers in the columns, and then go looking for mold growth. If there are no elevated numbers, good. Maybe you’re finished, at least for that room.

Here is a challenge question for you: Do you know what the most important mold markers are for water damage and elevated relative humidity? Aspergillus and Penicillium. The numbers for Aspergillus/Penicillium spores often alert you to the degree of mold concerns at the testing location.

After seeing what you can learn from comparing Asp/Pen numbers for the different areas sampled (except for the outside, which we already talked about being irrelevant), take a look at the two other species: Stachybotrys and Chaetomium.

Even though the per cubic meter counts are very low for them, the fact that they are present at all points to growth somewhere open to room air (or to a less-than-effective remediation job). These spores don’t just float in from the outside.

These are two of the molds that need more water than Asp/Pen and many other fungi. They are markers for leaks and floods, not for elevated relative humidity. Their spores are also less likely to become airborne, compared to Asp/Pen, so numbers, if they are present, will likely lower than those of Asp/Pen.

If I see even one spore of Stachybotrys in the chart, I’m saying to myself, “There is growth somewhere in the vicinity.” The same goes for Chaetomium.

So! Those are the main things you need to know about interpreting a lab report. Compare locations to track sources of growth and gauge whether elevated relative humidity is an issue at the house. With the latter, mold could be growing on furniture.

Molds that are common in houses are listed below, with a few words about what they look like under a microscope. Some of these molds will also show up on the lab report, but typically, if one of them has elevated numbers, Asp/Pen will also be elevated, with the exception of Cladosporium, which may blow in from the outside:

Molds requiring moderate moisture

Molds requiring prolonged wetness, i.e., higher water needs

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Next up, Onward to DIY Mold Clean Up, or, back to the Mold Topic Index.


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