What Is a Mold Air Test — And How To Read The Results?

A mold air sample test suctions air from your home across a sticky cassette and then sends this into a certified lab to count every spore under a microscope. This guide walks you through exactly what to look for and when the numbers require action.

What is the Lab Air Test?

A lab mold air test, also called a spore trap test, works by drawing a measured volume of air through a sticky cassette for capture, whatever is floating in it. That cassette gets sent to a certified lab where technicians count every biological particle under a microscope and identify it by species. The result is a precise list of every mold type present in your air, measured in spores per cubic meter.

Air tests are the most common type of mold test ordered by inspectors, doctors, and industrial hygienists because it gives you species-level detail that real-time devices cannot. If your doctor suspects mold illness, or if an inspector finds something suspicious during a visual walkthrough, a lab air test is usually the next step. It tells you not just that mold is present, but exactly what kind and how much.

Two Types of Mold Air Tests

There are two main types of lab air tests. Both use a cassette to capture airborne mold, but the lab handles them differently and each one answers a different question.

Non-Viable Spore Trap

This test looks at all the mold spores on the cassette regardless of whether they are able to grow. The lab examines the slide under a microscope and identifies every spore it can see, living or dead. This is the faster option and is used for quick diagnosis of what is floating in your air.

Non-viable testing is what most inspectors use as the standard air test. Results come back in one to three days. The tradeoff is that some mold types look identical under a microscope (Aspergillus and Penicillium, for example, are always grouped together) so you may not get exact species-level identification for every mold present.

Viable Cultured Trap

This cassette is kept in the lab for about five days so the mold can actually grow. The lab watches to see which spores develop into active colonies. Only spores that have grown since the initial collection are considered viable. The rest are considered denatured, meaning they are dead and no longer propagating in your home.

Viable testing takes longer, but it answers a question the non-viable test cannot: is this mold actively growing, or is it just dead material? It also allows the lab to identify molds down to the exact species, which matters when your doctor needs precise data or when the non-viable results are ambiguous.

Claro typically uses Viable Cultured traps after treatment to confirm any mold present can no longer grow.

When we recommend remediation

Any one of these conditions on its own is enough for us to suggest remediation after looking at air tests.

Immediate

Toxic marker mold present

Molds like Stachybotrys ("black mold") or Chaetomium are dangerous even at very low levels. A single spore on a test is a red flag because these molds can cause serious neurological health issues beyond allergy-like symptoms.

Threat

Elevated spore counts

Spores over 1,000 spores per cubic meter for any single mold type, or indoor levels significantly higher than outdoor levels.

Example Test results

Below are three test that we took across three different homes all on August 14, 2025. They are a good example of the range of results you may see in your home.

Example 1: treatment not suggested

📍 Brentwood, TN · Employees concerned about mold sickness

Both offices had nearly identical mold loads — consistent, which rules out a localized source.

Molds present are common indoor species not typically linked with illness at low levels.

All spore counts below 1000 spores/m3.

No visible mold observed during inspection.

We did not suggest treatment and the landlord did not proceed.

Example 2: Clear in crawlspace, hasn't fully spread to home yet

📍 Nashville, TN · Pre-sale inspection flagged by home inspector

The bedroom test looks fine. No single species above 1000, no marker molds. Under most rubrics, that passes.

The crawlspace tells a different story: 1,840 Basidiospores, 960 Penicillium — and 1 Stachybotrys spore.

One Stachybotrys spore on its own triggers treatment. Always. That mold is toxic and can cause serious illness.

Was still clear in the living space, but only because they caught it in time.

Example 3: A serious mold problem in the living space

📍 Antioch, TN · Community home, two-zone test

One Stachybotrys spore in the bathroom — people are using this room daily. Immediate treatment required.

Stachybotrys spores are heavy and hard to aerosolize. Catching even one means the underlying colony is substantial.

Aspergillus/Penicillium over 500 in both zones. Combined with visible growth, a clear water source is feeding an active mold problem.

This home needed, and received, remediation from Claro without delay.

Back to The Claro Rubric

How to Read Surface Test Results