Very moldy building interior (C) Daniel FriedmanMold Tests vs Mold Problem Diagnosis - a mold test may not accomplish what you thought

  • MOLD TEST vs. PROBLEM DIAGNOSIS - CONTENTS: A critique of popular building mold contamination tests & test methods.Can mold tests reliably predict the presence or absence of an indoor toxic or allergenic mold problem? Why is a building inspection an important part of diagnosing a mold problem? Advice to clean up small areas of mold without testing. When to inspect further for hidden mold contamination in buildings
  • POST a QUESTION or READ FAQs about the difference between a simple mold test and more accurate procedures to find out if there is a mold contamination problem in a building

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Mold test vs. mold contamination detection:

Here we distinguish between tests to identify mold in a building and procedures to determine whether or not there is a mold contamination problem in a building.

Following that distinction we continue by listing the specific reasons to test for mold or cases when mold testing is appropriate and useful.

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The Usefulness of Mold Testing vs. Mold Identification

Alternaria mold spores and hyphae from an indoor surface (C) Daniel Friedman15th Annual North Carolina/South Carolina
Environmental Information Association Technical Conference
Myrtle Beach, SC
Daniel Friedman 23 September 2005, updated thorough 11/19/2013

Abstract: In this article series we explain the difference between a mold test and a procedure to reliably identify a mold problem in a building.

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We describe the validity of nearly all of the popular mold testing methods currently in use, pointing out the strengths and weakness of each approach to mold sampling in the indoor environment, beginning with air sampling for airborne mold levels indoors.

We explain that a "mold test" in a building, used alone, without an accompanying expert inspection, may be of little use because of the potential for major errors in the test procedure and test mechanism and because even if the test successfully collects evidence of building mold contamination, the mold identified may not be the most serious mold contamination present.

Finally, even if a mold test could properly identify the presence of the most serious mold contaminants present, it may be insufficiently diagnostic to give any guidance whatsoever about where the mold problem reservoirs are actually located, the extent of cleanup needed, and the cause of the mold growth.

All of those questions will require an additional expert investigation, evaluation, and possibly further testing before a mold remediation plan can be prepared. Nevertheless, as we outline in topic 2 below (a separate paper) there are reasons to test for indoor mold.

This discussion of the usefulness and validity of mold tests is divided into two main topics:

Mold testing discussion can be divided into two main topics, the first of which is discussed in this paper.

  1. MOLD TEST REASONS - reasons why in some conditions it is appropriate, useful, and cost-justified to test for mold and to identify the kinds of mold that are present in a building. We emphasize that for small areas of mold contamination, generally where less than 30 square feet of contiguous mold is present, simple building cleaning and renovation procedures are all that's needed and testing is usually not appropriate. Most building mold contamination falls in this first category.

    Separately at MOLD / ENVIRONMENTAL EXPERT, HIRE ? we provide guidelines to help decide when it is probably justified to bring in a mold expert to perform mold inspection and testing in a building.
  2. MOLD TEST vs. PROBLEM DIAGNOSIS - what is the difference between "mold testing" and "mold identification", and what good are consumer mold test kits. Why are "mold tests" alone of little use and insufficiently diagnostic?

Mold "Testing" vs. Mold "Problem Identification"

We are "making up" this temporary distinction to make clear an important point.

Mold Testing a building for the presence or absence of a problematic level of mold is unreliable if by "testing" one means a simple air test, an arbitrary surface or vacuum test, a swab test, or any culture method used alone and without a careful and complete inspection of the property. In particular, failure to detect problem levels of problem mold with an air, culture, swab, PCR or similar test (used alone) is not sufficient to conclude that there is no problem.

1. Airborne particle levels vary widely over short time intervals. What's in the air in a building varies enormously, possibly by a factor of thousands, over just a few minutes, depending on things like the level of activity, mechanical disturbance of dust, fans being turned on or off, hot air heat or central air being on or off, and more subtle changes in humidity, etc.


2. Mold Culture Tests whether from a "home test kit" culture plate or a swab are unreliable as a characterization of presence or absence of mold because

  1. only about 10% of all of the 1.5 million mold species on earth will grow in any culture under any condition,
  2. because what grows on a particular culture may be what likes that culture not what is the dominant problem
  3. because accurate speciation of some of our problem groups such as Penicillium sp. and Aspergillus sp. require arduous multiple cultures under very controlled conditions for reliable results.


3. PCR tests are highly accurate in identifying individual molds, if you know what you're looking for. PCR is not reliable as a broad spectrum scan to find what's in a building.


Mold Problem Identification, as we are speaking here, is an important part of a building investigation for mold (or other allergen) problems.

By this we mean, an investigator should be charged to identify the presence of problematic mold, including no less than the following:

  1. first, the evidence that problematic levels of mold are present and that the predominant genera/species are ones which can be expected to be toxic or highly allergenic;
  2. second, the evidence that a large problem reservoir exists;
  3. third, the location(s) of the problem reservoir;
  4. fourth, the underlying causes for the presence of the problem reservoir.

This information permits preparation of a remediation plan to specify the cleanup needed and the building repairs needed to avoid simply producing more mold.

Key in a Mold Problem Identification investigation is the actual visual examination of the building, its history, its leaks, and other physical evidence.

As a part of such an investigation, samples are collected of visible mold to distinguish cosmetic from problematic material, and other samples might be collected to examine the level of moldy dust settled in building areas where mold is not present. Additional samples may be collected for comparison baselines such from outdoor areas or from non-complaint areas in the problem building.

A thorough building investigation will include sampling or "tests" to identify the presence of mold and to identify the dominant problem molds by genera and often species.

By contrast, a quick and simple "mold test," particularly a random spot check, is of little value by itself: grabbing a 90 liter air sample or putting a settlement plate in a closet for an hour is not a reliable building characterization for mold, and a tape sample of the single square foot of mold in a building is unnecessary.

Clean up small areas of mold growth without testing

If there is no large mold area, no leak history, no at-risk occupants, in sum, if you simply have a little moldy area, just clean it up, and spend your "test kit" money on cleaning supplies or dinner out. Small amounts of mold can often can be cleaned-up by the occupant or owner provided that person has no special allergy or risk regarding mold.

Some states define "small" as less than 30 sq.ft. of contiguous mold. Your own area may use a different criterion. Larger areas of non-cosmetic mold are likely to require work by a cleanup professional. If you think you need to hire someone,
see MOLD EXPERT, WHEN TO HIREor more detailed help in deciding when and how to proceed.

Are Home Test Kits for Mold Useful? Accurate?

Settlement plates, culture media, or swabs which are later cultured, used alone for building mold risk analysis are invalid methods which risk both false positive results (saying there's a problem when there is not) and false negative results (missing an important problem). More about this is in this article and you can read in greater depth

What about other do-it-yourself tests? Amateur mold "testing" by a homeowner, using a tape lift of visible mold, perhaps with some good advice on where to look, might be an inexpensive way find out that the "black mold" on the floor joists is a "cosmetic-only" mold, thus avoiding the cost of a more expert professional building investigation/remediation.

However anyone using this approach should understand that it is incomplete and superficial: you might collect your sample from a spot which is not representative; you will not address the risk of hidden mold in building cavities; you will not have expert mold remediation advice; you will not have baseline data to support a later clearance test after cleanup, finally, you risk leaving another problem in the building. These warnings should be considered carefully where large areas of mold are already visible or at-risk occupants are involved.

Of the mold samples sent to our lab by owners who have had no collection advice, we find that "black molds" seem to be over-represented and we suspect these are often not the real problem in the building. The mold the owner sees may be simply the indicator of moldy conditions.

Lighter, harder-to see molds in the Penicillium sp. and Aspergillus sp. families, for example, are under-represented in owner-collected samples (based on our field experience and on our review of statistics of samples sent to Dr. J. Haines at the N.Y. State Museum for identification) because these genera are often more difficult to see.


Continue reading at MOLD / ENVIRONMENTAL EXPERT, HIRE ? for more about these questions and their answers.

Suggested citation for this web page

MOLD TEST vs. PROBLEM DIAGNOSIS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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