Which Mold Tests Are Worth It

This is one veteran inspector’s field method. The CIRS testing protocols, ERMI and HERTSMI-2, and how they are used, are covered in our Mold Testing & Remediation Guide.

A tape lift shows whether a surface has growth, what kind, and roughly how much. It finds mold you cannot see and is cheap enough to take dozens. One veteran inspector relied on it for almost twenty-five years.

Evidence: Inspector's practice (precautionary). Current guidance: EPA and IICRC S520 treat surface sampling as a supporting tool; results for legal use need an accredited lab.

A pump pulls air onto a dish of mold food, and living spores grow into colonies that can be identified. Unlike other air tests, it can tell Aspergillus from Penicillium, which helps reveal whether there is one source or two. "Aggressive" means stirring the settled dust near the sampler, since spores sink into dust over time and a still-air sample can miss them. Its limits: results take days, dead spores do not grow, and Stachybotrys rarely grows on the plates. Treat it as backup to tape.

Evidence: Mixed or limited evidence. Current guidance: stirring the air is standard in asbestos clearance and some mold clearance protocols, but many mold guidelines use undisturbed sampling, so check how each report's samples were taken before you compare results.

This is the test most inspectors use. A lab counts spores caught on a sticky surface, and results come quickly. But the small round spores of Aspergillus and Penicillium look alike, so they are lumped together, and the test cannot show where growth is. Mold sealed inside a wall rarely shows up.

When you read a report, look for the raw count, the number of spores actually seen, rather than the larger per-cubic-meter estimate. The inspector this work builds on liked to see Aspergillus/Penicillium raw counts in the low single digits, and began looking for a source when they climbed above that. Any Stachybotrys or Chaetomium at all meant searching for growth, because these spores do not drift in from outdoors and are heavy enough that even low numbers can signal real growth.

Evidence: Inspector's practice (precautionary) for these targets. Current guidance: no health-based numeric limit for indoor mold exists (EPA); mainstream interpretation guides also treat Stachybotrys or Chaetomium at any level as a sign of indoor growth.

An open dish catches only whatever happens to fall into it. In one inspector's side-by-side test, a stirred settle plate grew about a quarter of the colonies a pump sampler caught. Black colonies are almost always a common outdoor mold, not the feared "black mold." These kits tend to undercount and can give false comfort.

Evidence: Inspector's practice (precautionary).

This is the one lab test the inspector found actionable on its own, because it points at a known source: the central cooling system. Wiping dust from the slots of a supply vent cover with a sterile swab can reveal what is growing deeper in the system than anyone can reach. DNA tests count fragments, so expect big numbers, and treat the result as a clue.

Evidence: Inspector's practice (precautionary).

These can confirm mold is growing somewhere, but not where or how much. Sensitive versions are costly, and cheaper ones miss a lot. Finding and removing the growth stops the gas.

Evidence: Inspector's practice (precautionary).

This page is for education only. It is not medical, legal or engineering advice. The inspector whose work this builds on was an environmental consultant, not a physician. Talk with your doctor about health concerns, and use licensed professionals for electrical work and large mold jobs. Products, prices and labs mentioned reflect the years they were recorded and may have changed.

Source: the field work of environmental inspector May Dooley, MS, MA, CMC

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