Mold clearance testing: the samples and the report

Clearance testing, explained

The samples a clearance test takes

No single sample can prove a job worked. A clearance test is a small set of samples that only make sense side by side. Which ones a project needs depends on what was found at the start and who lives in the home.

Sample	Where it’s taken	What it shows	When it’s used
Work-area air	Inside containment, near where the growth was	The kinds and amounts of spores in the cleaned space	Every clearance
Outdoor baseline	Outside the home, at the same visit	The normal background for that day, season and weather	Every clearance
Unaffected room	A room the problem never reached	What normal looks like inside this particular house	Almost every clearance
Surface (tape lift or swab)	Cleaned framing, subfloor or other materials	Whether growth or settled spores remain on surfaces	When surfaces were cleaned rather than removed
Settled dust	Horizontal surfaces in and near the work area	What has built up in the dust, which air samples can miss	Sensitive households and larger projects
Mycotoxin panel	Settled dust, compared with the panel taken before the work	Whether mold toxins remain after the mold is gone	Mycotoxin projects and mold-sensitive households

The outdoor and unaffected-room samples are not extras. Outdoor spore counts can swing a lot between a dry morning and a humid afternoon, so the baseline has to come from the same visit. Without it, a work-area number has nothing to be compared with.

What a pass means

The mold remediation industry’s main standard, IICRC S520, describes indoor mold in terms of three conditions. Clearance samples are read to decide which one the work area is in now.

Condition	What it describes	Clearance meaning
Condition 1	Normal fungal ecology: the kinds and amounts of mold you’d expect in a building without a mold problem	Pass
Condition 2	Settled spores or mold fragments that came from growth elsewhere	Fail. More cleaning needed.
Condition 3	Actual mold growth, active or dormant	Fail. Growth was missed.

Clearance doesn’t mean zero mold. Every building has some, carried in on air and shoes. A pass means the work area now looks like a normal space rather than one that recently had a problem. In practice, that usually comes down to a handful of pass criteria written into the scope before work begins: work-area air similar to or lower than outdoor air, with a similar mix of molds; results in line with the unaffected room; water-damage molds absent or at trace levels; clean surface samples; and, on mycotoxin projects, a repeat panel that meets the target agreed at the start.

How to read a clearance report

An air sample report lists the spore types the lab identified and how many it counted, usually per cubic meter of air, for each sample location. On its own a number means little. The comparisons are what count:

What to compare	What a passing result usually looks like	What raises concern
Work area vs. outdoors	Similar types of mold, at similar or lower levels	Types inside that are rare or absent outdoors
Work area vs. unaffected room	Comparable results	Work area noticeably higher
Water-damage indicator molds	Absent or at trace levels	Stachybotrys, Chaetomium or elevated Aspergillus and Penicillium types in the work area
Hyphal fragments and debris	Low	Elevated, suggesting fine dust remains
Surface samples	No growth, only normal background	Hyphae or dense spores on a cleaned material

Beyond the numbers, a clearance report you can rely on should show the lab’s name, the date and time of each sample, a map or description of each location, the outdoor conditions at the visit, the raw counts rather than just a verdict, and a chain of custody from the site to the lab. Our answer on what mold spore counts mean walks through a sample report line by line.

Who should collect the samples

The person who takes clearance samples decides where they’re taken, and placement affects results. That’s why many owners, insurers and attorneys prefer an independent assessor to sample the remediator’s work. Some states that license mold professionals require that separation on regulated jobs. Indiana doesn’t license mold remediators, so for Indiana homes it’s a matter of preference. We sample our own projects, share every original result, and are glad to coordinate with any qualified assessor you choose. Whoever does it, ask them to follow the sampling plan written before the work began, not one chosen after.

If a sample fails

A failed sample is the test doing its job. The usual cause is fine dust left on horizontal surfaces, in the tops of framing or on the inside of the plastic. Sometimes it points to a small area of growth that was missed. The area stays contained, the likely source is found and cleaned again, the air is allowed to settle, and the failed locations are resampled. Clearance testing is the last item on the remediator’s post remediation verification checklist, so a fail usually sends the job back one or two steps on that list rather than to the start.

When clearance should include mycotoxins

Mold samples measure mold. They can come back clean while fine dust carrying mycotoxins remains on framing or in nearby rooms. On any project where toxins were part of the problem, and for households where someone is sensitive, clearance should include a repeat mycotoxin panel compared with the one taken before the work. Our page on mycotoxins after remediation explains why they can linger.

After clearance: checking over time

Clearance describes the work area at the moment the job ends. It can’t promise what happens after the next heavy rain or a new plumbing leak. Families who want extra confidence often retest later with the same dust test used at the start, under normal living conditions. For the signs to watch in the months after, see how to know mold remediation was successful.

Clearance testing verifies the condition of a building. It doesn’t diagnose or treat any medical condition, and passing clearance isn’t a health guarantee. If anyone in the home has symptoms, please work with a doctor. With your permission, we’ll share the clearance report with them.