mold culture (C) Daniel FriedmanEvaluation & Survey of Toxic or Allergenic mold Test Procedures

  • MOLD TEST PROCEDURES - CONTENTS: Survey of building mold test procedures, mold contamination test methods, & mold test kits: a report on the accuracy, cost, effectiveness of various approaches for screening or testing buildings for mold contamination or for identifying mold contaminants. How to choose a mold test or mold sample method. How to avoid inaccurate mold tests.
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Building dust & mold test methods & procedures:

This article describes and evaluate the accuracy, ease of use, relative costs, reliability, and other features of various methods used to test the indoor environment for toxic, allergenic, or pathogenic mold contamination.

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Mold & Dust Testing Procedures: Valid and invalid mold testing methods & protocols. Are some mold test kits junk science?

Photo of mold on roof sheathing undersider in an attic - white mold (C) Daniel Friedman

While there are certainly cases in which mold inspection and testing are justified and ethical to perform, too often we see people spending on mold test kits, mold inspections, mold experts, and similar products and services which are unnecessary and sometimes inaccurate as well.

See mold EXPERT, WHEN TO HIRE for a discussion of when it is or is not appropriate, justified, and ethical to hire a mold consultant to inspect, diagnose, and advise about mold contamination in a building.

Mold Testing: Examining the Validity of Current Indoor mold Sampling Techniques

Ganoderma (C) Daniel Friedman

Readers: please see the full-text version of this presentation at MOLD TESTING METHOD VALIDITY

© 2010-2013 Daniel Friedman.

The illustrated power-point version of this document is at - © 2017 - 2004 Daniel Friedman, but involves larger files of images and data - if you are viewing this document from a low-speed line you should stick with the text version.

This paper presents a summary and critique of some popular methods used to examine indoor air quality to test for presence or absence of problematic levels of toxic or allergenic mold or other bioaerosols. We will describe and critique specific "testing" or "sampling" methods used to "test" buildings for mold in the course of a building investigation.

The appropriateness of testing at all is discussed on this and other pages at our website. our website includes more broad discussions of the overall approach to building investigation, as do many expert references cited at that web.

For a more comprehensive collection information about mold test methods see For more on "mold classes" (Cosmetic mold vs. allergenic mold vs. toxic or pathogenic mold) see MOLD CLASSES, HAZARD LEVELS and more references such as a mold Action Guide are at the end of this document.

Article Contents:

Introduction to Toxic mold testing and mold Sampling Methods

An IAQ or "mold investigator" cannot reliably identify a mold genera or species growing on a building surface by the naked eye. Despite the recent public fear created by media attention, including a now-refuted "Toxic black mold" Stachybotrys chartarum study involving infant illness and death, it is simply not the case that "black mold" in buildings is necessarily a danger to occupants.

In fact, having investigated many buildings quite carefully, I assert that in most cases the "black mold" that you see in buildings is most often an "indicator organism" telling you that conditions are right for mold formation.

We have often found more problematic molds in such properties, such as species of Aspergillus sp. or Penicillium sp. which are airborne, travel in the building, and are more likely to be bothering the occupants than a large, sticky, non-easily-airborne spore like S. chartarum.

These harder to see, often light-colored molds, are quite often missed entirely by inexpert owners and amateur "mold inspectors" who go on to collect, over-report the occurrence of, and react to the "black stuff." One result has been unnecessary expense for "mold testing" and in some cases unnecessary mold remediation. Some of our articles, as well as writing by others who study this field, address these problems and offer help in deciding what level of trouble and expense are appropriate.

In any case, mold in a building should be cleaned-up, and large amounts might require professional inspection and advice. before doing anything drastic or costly, get some competent advice.

Opinions Expressed in This Article

This is a working document and is incomplete. These views are undergoing and are subject to peer review and revision. (Critique from any reader is welcome).

Trained in building science, we perform on-site building investigations to evaluate the need for and extent of mold remediation in buildings in order to give mold remediation and prevention advice.

Also trained in mold and other particle identification (forensic microscopy), we operate our own aerobiology laboratory where samples, collected during an investigation, are examined. In the course of our field surveys we often collect multiple samples even at the same surface or building area, in order to study the relative effectiveness and consistency of the various methods, just as we test and compare other tools used to find hidden moisture and similar problems.

These extra samples, collected for purposes of scientific study, are not billed to our client. Our opinions about the usefulness of various methods derive from both study by other experts and by our own ongoing field and laboratory testing. Does everyone need to hire an "expert" like us to examine their home? Of course not. This article offers help in choosing mold sampling and testing methods and devices.

Other articles at this website offer help in determining when it's appropriate to hire an expert. The Minnesota Department of Health has useful advice [ ] about hiring an investigator too.

Consultant certification - who's an "expert" and do you even need one?

Where the extent of mold damage and/or the risk to building occupants justifies a professional survey, the inspection, sampling and testing performed, the laboratory determination of sample contents, and mold cleanup must be performed competently, lest the building owners/occupants face an unexpected health risk (someone makes a mess of problematic mold) or cost (a poor remediation plan or bad clearance testing leaves a mold problem and the work has to be done all over again).

Whoever performs sampling or testing needs to use effective methods for inspection and testing. For professional inspections, education and experience are required for this work as substantial costs and the health of present and future building occupants can be at risk. Consumers should review experience and education of whomever they hire to survey a building or to clean up an environmental problem.

Regrettably various mail-order "certifications" are available which are confusing to consumers, and even within organized professions such as industrial hygiene, environmental inspection firms, engineering firms, and home inspection companies, individual training, experience, and depth of knowledge vary enormously.

Consumers hiring an inspector or remediation company should consider the education, experience, and track record of people they may employ and should not rely only on a professed "certification." (Years ago our dog Katie became a "certified inspector," and received a full diploma from a national "certification" agency.

Try going to the "certifying" agency's website to see if, for simply mailing in a fee, or perhaps taking a weekend course, you, too, could become "certified" as a "mold remediator" or "environmental inspector.")

The CIH designation is a real credential as is P.E. "real" for certain specialties. but some CIH's and P.E.'s do not know building failures and leak tracing, and may match other "mold investigators" who are not familiar with mycology, aerobiology, air and particle movement indoors, microscopy, chemistry, proper ways to use equipment, how to evaluate the expertise of their "mold lab," or even what mold looks like.

The Pan American Aerobiology Association [ ] has recently completed and turned over to an independent testing agent [ ] a national examination specifically to test the competence of people identifying fungal spores, a test which was offered beginning in 2004. Look for this and other pertinent professional associations or certifications provided they are from "real" professions and professional associations. And look at the background and experience of the investigator. AIHA is also interested in further investigator and lab certifications.

Description & Critique of Contemporary Indoor mold Sampling, mold Sample Collection, & mold Testing Methods

Comments on the Validity & Shortcomings of Air Sampling (Spore Traps) to Screen a building for Toxic mold

Mold air sampler in use (C) Daniel Friedman

A collection device, slide, cassette, or tape are used with a calibrated air pump to collect airborne particles. we are not referring to culture plates which rely on passive collection or settlement of particles as these have even worse inaccuracies and errors than the reservations I describe about active air sampling described here. Some common examples of air samplers include:

  1. Impaction air samplers (Burkard™, Allergenco™) collect airborne particles through a venturi-slit onto a prepared microscope slide using a equipment incorporating a calibrated air pump and a static or moveable slide permitting single-use or time-lapse sampling. Our photo (left) shows an Allergenco™ slide impaction air sampler in use - what do you think happens to the detectable airborne dust and particle levels when the "air cleaner" is running versus when it's turned off?
  2. Cassette air samplers (spore traps) (Air-o-Cell™ and AllergencoD™) use a patented 37mm cassette connected to a calibrated pump (typically at 15 lpm). The cassette is used to collect airborne particles through a venturi-slit onto a proprietary media on a cover-slip which is in turn mounted onto a microscope slide in the laboratory.
  3. Cassette air samplers using an MCE filter cassette connected to a calibrated pump. The filter can be cleared and examined microscopically (qualitatively, counting is tough except with the bi-Air™), or used to prepare a culture, or both.
  4. Cassette-like air samplers use a calibrated pump connected to a patented stainless steel venturi-device which accepts a microscope slide prepared with a collection media.
  5. Anderson-type air samplers which collect particles directly onto a culture dish - for "viable sampling" to "test" for mold. Culture samples may be useful in some cases to better identify or to speciate mold which has already been found in a large reservoir. Otherwise it has limitations we discuss elsewhere in this document.
  6. Anderson-type impaction air samplers which collect particles on tape wrapped around on a drum or Rotorod samplers which collect particles on glass rods are used for outdoor pollen and spore counting and reporting in the IAAA allergy network. They are not well-suited for indoor building assessment though some folks use the high-error rotorod sampler indoors.

Comments on the Validity & Shortcomings of Air Sampling (Spore Traps) to Screen a building for Toxic mold

Burkard PAS (C) Daniel Friedman

But as a "mold test" for the presence or absence of a mold problem in a building, a negative air sample result is of little confidence.

As a measure of "mold exposure" quantitative analysis (spores/cubic meter) is invalid unless long-term time-weighted average measurements are made under all varying building conditions. While this is an important diagnostic tool, and one which we apply regularly, it cannot be relied alone on in the way some investigators would use it: dashing into a building and grabbing an air sample.

Air sampling as a "pass/fail" or "present/absent" test for mold in buildings is unreliable as a "mold test." Many variables cause a wide range of particle levels in air over short intervals.

However this method has a place in a thoughtful building investigation: air sampling can be useful as a background check for the possibility that there is a large reservoir source which has not yet been found in a building.

But a negative air test for mold result is of very little confidence, and quantitative work (spores/cubic meter) is invalid unless long-term time-weighted average measurements are made under all varying building conditions. our own time-lapse sampling proves that particle levels vary by a factor of 10,000 due to common variations in building conditions such as fan on off, human activity, mechanical disturbance of moldy stuff, etc.

Just below in this paper we illustrate this with two photos of slides of particles collected using the Burkard personal air sampler (left).

While this is an important tool it cannot be relied on in the way most "inspectors" would use it, dashing into a building and grabbing an air sample. See "Quantitative Analysis" comments below for an elaboration or see moldTesting: Air samples and their interpretation - a quick

  1. Spores are collected but not spore producing conidiophores, hyphae and other components are collected, making identification incomplete and more difficult than with tape or cultured samples.
  2. Spores are desiccated and may be damaged by the collection method, interfering with culture efforts if this follow-up step is needed.

In sum, air sampling is useful as a background screen for the possibility that there is a large reservoir source which has not yet been found in a building, and may be useful to compare relative particle levels between a problem area and a control area, or in an area before and after cleaning. Independent from spore counts, a qualitative analysis of an air sample by an expert technician can provide compelling evidence of a nearby problem mold reservoir in certain cases, for example if the indoor sample contains long chains of Penicillium or Aspergillus spores.

These spore chains are so fragile that they break apart quickly while traveling through the air. So spore chains found in (a pre-remediation) indoor sample, even if the total count is low, deserve some further thinking and investigation.

Mold in Air: Quantitative Analysis - "Spore counts" Vary by Orders of Magnitude

Low density mold spores (C) Daniel Friedman High density mold spores (C) Daniel Friedman

Our microscope slide photos above show two airborne particle samples collected at the same location, just moments apart in time.

Even without attempting an actual accurate count of particles per cubic meter of air, it is apparent from the significant difference in the densities of the two particle traces that the level of airborne particles varied enormously, even though the same instrument was used in the same location.

Examining particles on a slide to count mold spores/Meter3 of air, mold Spores/M2 of surface area, or mold CFU's - colony-forming units is a common practice in building investigations. These measures can be used to describe the results of some sampling or "mold testing" methods in building.

While there is no fixed (nor fix-able) standard of absolute allowable "spore counts" in air (we'd need a standard for every genera and species by toxicity, weight, mobility, etc.), investigators have now seen so many moldy and not-moldy buildings, and complaint and non-complaint areas that it's reasonable to have some general guidelines about what levels are probably a problem and what levels may not be a problem.

Acceptable mold Levels: While there is no well-established quantitative standard for fungal spores on surfaces or in air, mold contamination is considered present in a building when the total mold spore concentration per cubic meter of air is above 10,000. (Baxter, ETS).

Acceptable levels for individual mold species in buildings vary since species toxicity varies widely as does spore size, weight, and other features which affect risk to building occupants. E.g. Aspergillus/Penicillium in a "clean" residential building study was at a mean of 230, in buildings known to have a moisture or flooding problem it was at 2235 and in mold contaminated buildings the figure was 36,037.

Surface samples of mold: the presence of toxic or allergenic mold as a dominant particle in any sample (surface or air) is usually a cause for further investigation or remediation.

The presence of incidental occurrences of toxic or allergenic material in surface samples requires interpretation in light of other building conditions, type of particle (spore chains), and other factors.

For example, in a pre-remediation building where occupants have building related complaints and mold contamination is suspected, even a modest indoor level of 500 spores/M3 of air might suggest a problem if those spores formed a high percentage of the total indoor spore count and only a low percentage of the corresponding outdoor spore count taken as a control. our own field experience is similar to the counts suggested by baxter.

Since indoor environments in the U.S. and many other parts of the world are similar in conditions and often in building materials, it is likely that these levels are not very dependent on region of the country.

Warning: interpret all quantitative data with great caution. Individual samples of particles in air show tremendous variation from minute to minute, making "ok" test results a thing to view with care. In situations of particular risk additional or periodic testing should be considered.

However, because indoor conditions of mechanical disturbance, ventilation, occupancy, and use vary widely over short intervals of just a few minutes, an indoor "mold spore count" is at high risk being inaccurate, incoherent, and confounding.

Recipients of such reports are may not realize the distinction between highly precise results (lots of decimal places) and results which are fundamentally accurate or inaccurate, depending on the design of the sampling plan and the variation in building conditions during the sampling interval. Unless there is good experimental design, quantitative results are precise (lots of decimal places in the answer) but almost certainly wrong (off by a factor of thousands) as a characterization of a building.

Therefore quantitative studies are most useful as part of a more broad qualitative approach, indicating either relative differences in mold levels between a control area and a problem area or the relative change in building conditions before and after cleaning.

They are much less reliable as an absolute pass/fail criteria. Other substantial quantitative report issues other than accuracy include wide variation among labs in counting and skill levels, and more interestingly, the lack of and virtual impossibility of establishment of valid quantitative standards for mold exposure.

For example, two different particles have different toxicity, different air movement; two of the same particle can vary in toxicity depending on supporting growth surface.

Shortcomings of Quantitative Analysis of mold Spores in Air

  1. Quantitative Analysis producing low results is unreliable: building conditions vary enormously, causing huge variations in what particles may be found in the air at any given time. our own time-lapse sampling suggests that particle levels vary by a factor of at least several orders of magnitude due to common variations in building conditions such as fan on off, human activity, mechanical disturbance of moldy stuff, etc.
  2. Quantitative results which are superficially similar between indoors and outdoors may be misleading: An outdoor "Pen/Asp" count of 500 spores/M3 may have captured a genera or species which is completely different from a corresponding indoor "Pen/Asp" count which also found 400 spores/M3.
  3. Quantitative results which seem "low" and qualify as a "clean building" may be misleading: a lab reporting an outdoor "Pen/Asp" count of 700 and an indoor "Pen/Asp" count of 450 may look like an acceptably "clean" building - the indoor count is "below the outdoor count." but suppose in fact the outdoor "Pen/Asp" is actually an unidentified amerospore, or a basidiomycete mis-classified, or is a common outdoor species of Penicillium, while the indoor "Pen./Asp" is actually representing Aspergillus niger?

    This is an argument for doing some subsequent culture work or better lab microscopy (Aspergillus niger can be identified by light microscope alone.) In this case the "low" level of 450 spores may in fact be a weak indicator of a large problem mold reservoir in the building.

More about air sampling, spore count methods, and their validity

Comments on the Usefulness & Validity of Adhesive Tape Sampling for mold or Other Particles

Clear cellophane tape is pressed into a sampled surface, then removed and affixed to a clean surface such as a plastic bag or a microscope slide for mailing to a lab. The lab prepares the tape for microscopic examination. For mold genera and species identification the tape is examined in the laboratory. Tape samples can also be cultured (see Culture discussion below). This is the least-expensive collection method available, and is a preferred tool.

Using clear adhesive tape pressed into a surface to be tested is the first choice recommended method for identifying mold in a building, particularly when combined with visual inspection as part of a mold investigation, per AIHA and other expert sources. This method permits rapid identification of genera (family name) and very often species (individual member name), particularly when the mold sampled has uniquely-identifiable spores or where the sample collects the conidiophore or spore-producing body as well.

In some cases genera determination alone is quite sufficient as the some of the common problem-genera (Penicillium sp. and Aspergillus sp.) do not have non-problematic members which grow in buildings. Speciation is more likely to be needed when doing medical diagnosis. Tape samples can also be cultured if additional speciation is needed. Since tapes can collect the conidiophores and hyphae (when tape spot is chosen with some thought) they give more data than an air or vacuum sample.

For building where large amounts of mold are found or suspected, tape sampling is a qualitative approach which is usually quite successful in addressing the basic question: is there a problematic genera which requires professional remediation? Combined with a visual inspection to locate target areas of risk and to find visible problems, it is the most essential component of a building mold investigation and is the method recommended by experts writing in the field and by the AIHA's own training materials.

Tape samples are the preferred method of collecting surface samples in buildings. Tape pressed into appropriate portions of suspected mold growing on a surface collects the most material from the surface and often includes sufficient structural material to identify the dominant problematic genera and species present. A properly collected sample is likely to contain both fungal conidia, conidiophores, and hyphae, the latter two of which are important aids for speciation. Tape samples of building dust and even tape samples of moldy carpet are also generally useful in this manner but have some limitations discussed below.

Determination of mold genera:

Nearly all building mold genera can be determined by light microscopic examination of tape samples. In the majority of building investigation cases the key question is "is there a problematic genera (toxic or allergenic) requiring containment and professional remediation?"

This can almost always be completely answered from genera alone. This is because within the more common troublemakers, their non-problematic member species may not occur in buildings. For example, Penicillium notatum, used for the drug penicillin, does not grow in buildings! If you find Penicillium sp. in a building in quantity it needs to be remediated.

Determination of mold species:

Speciation of many mold genera can also be determined from tape sample material alone in many but certainly not 100% of cases. Some examples of easily speciated molds from among the most common genera and species found in buildings: Cladosporium sphaerospermum, C. cladosporioides, Ulocladium chartarum, Taeoniella rudus, Pithomyces chartarum, Stachybotrys chartarum, Chaetomium globosum, Chaetomium aureum, Aspergillus niger are just a few examples.

A good tape sample which collects the conidiophore and hyphae makes speciation possible for many molds. Many other airborne spores appear in buildings and can be similarly speciated, but are not building molds. Other airborne molds such as the Aspergillus and Penicillium families are probably a sufficient hazard in buildings that if they are present in a large reservoir, speciation is not needed to decide to remediate.

Shortcomings of tape sampling:

  1. Everything depends on where you stick the tape. Investigators and ordinary building occupants tend to collect that which is easy to see - "black mold" and may miss more important, more health-risky light-colored and highly airborne genera (Aspergillus, Penicillium) which are also present but more difficult to see. An expert looks for mold-suspect material that seems to represent the dominant presence in an area by color, texture, and growing surface material. It would be unusual for there to be only a single genera/species of mold in a mold-problem building. Looking and taping requires some guidance and education.
  2. Some smaller airborne mold spores do not settle out of air rapidly and might appear equally as plated-out on walls as in dust on horizontal surfaces. In building inspection to search for an unidentified problem source, samples of surface dust may under-represent the presence of these molds, though where a substantial airborne presence exists we have always found a surface dust presence as well. by contrast, properly collected tape samples from visible mold growing on a surface does not suffer this shortcoming.
  3. Speciation of genera may be needed for special medical diagnostic reasons. From spores alone in any sample method, two of the most widespread problematic genera can be speciated only to a few cases. (Aspergillus niger for example.) Therefore for medical use, tape speciation of some genera is too limited, in particular if the sample collects only spores - a problem which can occur if tape is pressed into dust rather than into an area of growing mold, or when tape of a mold colony is pressed into a spore-packed center of a mature colony instead at the edges where the new colony growth and conidiophores are easier to find. A little knowledge of mycology is useful to professional building inspectors.
  4. When growing conditions become unfavorable some molds change form into an encysted or encapsulated dormant state, forming fungal perithecia, cleistothecia, or pycnidia which may be collected as "black stuff" from building surfaces (particularly wood). While often one finds identifiable material among perithecia that cant' be assured. Culturing of such samples may produce an identifiable fungus if by luck the right culture media is selected.
  5. Tape sampling is qualitative, not quantitative. Most experts and competent labs will offer a description of the density of fungal material found in the sample using non-standardized terms like Level 1-2-3-4 or Light, Medium, Heavy, or Dominant, Present, and Incidental. These terms lack a standard definition but are of some use provided the lab has and can provide their own standard and definition.

In sum, the determination of the presence of a building mold problem (toxic or allergenic) vs. cosmetic mold can usually be made from tape samples alone.

For more information on tape sampling methods about tape sampling how to collect and send a tape sample to a laboratory

Vacuum samples for mold

A collection canister is connected to an air or vacuum pump which is used to draw particles onto a filter-surface or into a special collection container. The lab clears the filter onto a microscope slide, washes the filter onto a microscope slide, or uses another method to transfer particles for examination by microscope for preparation by culture.

Surface vacuuming test for mold

Spore traps (C) Daniel Friedman

Vacuum samples can be useful for testing soft goods (clothing, bedding, curtains, carpets) for high levels of contaminated spores in a qualitative approach. Our photo (left) shows Zefon™and an AllergencoD™ air sampling cassettes that work well for surface and insulation particle collection as well.

We particularly like vacuuming a number of surfaces in an area using a single collection device as a less-costly way to make a more confident inspection of the level of contamination by moldy dust in buildings with a known problem.

We also use this method as part of a mold clearance inspection to evaluate the thoroughness of both the containment system and the general cleaning effort. For example we may collect a sample of vacuumed surface dust from 10 different surfaces in 5 rooms on a floor of a home, forming a more broad screen for moldy dust than single tape lifts of surface dust.

We've found wide variety in levels of mold found growing in or on carpets, depending on a number of variables including even the level of other dirt present in the carpeting. Some experts question this measure. Carpet vacuuming for mold is interesting as a pre and post remediation baseline data source for areas out of the remediation/containment area, but for any carpet this method quickly overloads a particle sampler.

Shortcomings of surface and carpet vacuuming for mold

  1. vacuuming may not collect identifying structural components of mold as well as tape and will almost certainly damage or destroy the structures which it collects, imposing some limits on identification
  2. vacuuming will not collect all of the material on a hard surface (which tape handles well). Particles which are easily lifted by the airflow into the canister will be over-represented compared with sticky particles which are adhered to the test surface. This problem is particularly sensitive to the flow rate (LPM) used. A low-flow rate (1LPM) avoids a sample overload problem (too many particles, can't read the sample) but may fail to collect or under-collect certain particles. A high flow rate improves particle pick-up but then limits the number of sample sites (increasing test cost) in order to avoid sample overload. We suspect that no vacuum method We have tested could reliably pull mold or debris reliably from deep inside a heavy upholstered couch.
  3. Carpet vacuums and some furniture or drapery vacuums will either be overloaded or restricted to culture (to which We have already objected).

Shortcomings of vacuuming insulation for mold

We love this method, but one must take care not to overload the sample. If insulation is not exposed for testing one needs to make a sufficiently large opening to agitate and then vacuum the insulation - we use a 4" square opening and take care to avoid vacuuming up simply a collection of drywall dust.

Vacuuming building cavities for a mold screen

Vacuuming building cavities is a popular screening practice to look for mold reservoirs. The investigator is trying to explore wall cavities while doing minimal or no visible damage.

A wall-check™ system has been marketed for this purpose and several manufacturers have copied the basic idea: a receiving Air-o-Cel™ or MCE filter cassette is attached at its inlet side to a tube which is inserted as a probe into a wall cavity, permitting creation of only a small hole. The outlet or pump side of the test device is connected to a pump and operated, typically at 15 lpm. Where We have tested this method we have experimented with both passive collection (what most investigators use) or aggressive collection (banging on the wall/ceiling at various points to attempt to dislodge and stir particles).

Short duration samples, 1-2 minutes using an Air-o-Cell ™ permit a comparatively large number of samples to be collected in a reasonably short interval. Long duration samples, perhaps for up to two hours, are collected using an MCE filter cassette.

Shortcomings of vacuuming building cavities through a tube but our testing strongly suggests that this method is very unreliable for characterizing wall contents. We do not believe that enough air movement is created in the wall cavity (sucking any lpm flow through a small diameter tube) to reliably collect what could be a severe mold reservoir that happens not to be right next to the probe. Further if the cavity is insulated there will be virtually no air or particle movement except from very close to the probe.

Vacuuming exposed insulation for mold

See INSULATION MOLD CONTAMINATION TEST for details about the problem of mold contaminated building insulation.

At many investigations we have found a large hidden mold reservoir in building insulation, particularly fiberglass insulation in attics under roof leaks over drywall, and in crawl spaces which have been damp or wet. We have also found very moldy fiberglass in basement ceilings after moldy surfaces and debris have been removed (such insulation should have been removed during the remediation). our method is to agitate the target insulation (simply poke it with your flashlight or a ruler), followed by holding our vacuum cassette an inch or two away from the insulation surface.

This reliably picks up particles from the insulation without overloading the sample with fiberglass. (A baseline comparison sample collected in nearby building air before any such agitating sampling is also needed.) This method has been remarkably successful in finding and allowing the removal of several "mystery" problems in buildings where severe mold-related complaints were heard.

Any of several types of vacuum cassettes are used to collect dust from a surface. We use Air-o-Cel ™ cassettes and MCE filter cassettes. We am experimenting with vacuum cassettes loaded with high-adhesive tape. The contents of the cassette may be examined by light microscope or may be used for preparation of cultures.

One special (and costly) cassette method collects dual samples permitting both direct examination and culturing. This method may be used for both qualitative and quantitative analysis, depending on collection method details. It is best suited for sampling dust from surfaces and from soft goods such as carpeting or upholstered furniture.

It's strength is its use in examining multiple hard surfaces with relatively low levels of debris (avoiding sample overload) or individual soft surfaces where tape may not collect particles imbedded in the surface, and in collecting dust from multiple locations in a single cassette as a building dust scan for mold.

Comments on the Validity of mold Culture Tests to "Test a building for Toxic mold"

mold culture (C) Daniel Friedman

Mold cultures involve the collection of particles by air sampling pump, by gravity settlement, or by lift from a surface using a swab or tape. Some sampling equipment (Anderson™ spore traps) can collect spores directly into a petri dish of culture medium, and are used for "viable spore sampling in air."

The mold sample by pump, gravity, tape or swab is in any case applied to one or more petri dishes of culture media for incubation and subsequent examination of the growth product.

Mold culturing is useful for genera speciation once you have collected a single or dominant sample whose importance (frequency in the building) you already know.

As a "home test kit" for the presence of problematic mold in a building this is an unreliable method, as we describe below at "shortcomings."

Mold Cultures are indeed useful for:

Shortcomings of culturing mold samples

Alternaria mold spores and hyphae from an indoor surface (C) Daniel Friedman

While this is an important tool which has a place in our arsenal, mold culturing is questionable as a means to characterize a mold risk in a building, particularly if it reports the absence of a mold problem. The objections listed below mean that field investigators must collect samples with some care and interpret lab reports with some caution.

  1. Roughly 90% of all molds on earth will not grow on any culture medium under any condition. Others are quite difficult to coax into growing on culture, even with careful methods. So if you buy a "home test kit" that uses a single culture plate, you're 90% wrong when you open the container. To be fair, it might be that many common indoor problem-molds will show up in certain cultures, but these numbers still hold.
  2. The toxicity or allergenicity of a specific mold (genera/species/strain) may vary widely depending on what it's growing on. So even a "toxic" building mold might be low or non-toxic when growing on certain substances. Molds that grow on cultures may produce very different structures and have different medical characteristics than when growing in nature or in a building.
  3. Cultures may name the wrong mold as "the problem": Cultures have a high risk of both missing the problematic spore and of indicating that some other spore is the dominant or problem in a building. For example, to speciate one of the more than 100 members of the Aspergillus genera requires culturing the sample on four different media, simultaneously, comparing subtle things like growth rate among morphologically similar species. We believe that virtually no lab uses that troublesome procedure outside of university research and medical laboratories.
  4. Settlement plate cultures (such as "home test kits") rely on gravity, making any comparison of "spore counts" dead wrong - different spores are of different sizes and masses, and settle out of the air at different rates. This over-states the presence of big heavy spores (like Stachybotrys chartarum) and under-states the presence of small light spores (like Aspergillus versicolor) in a given sample. These small spores (2-3u) tend to stay airborne due to very slight indoor convection currents (e.g. heat from lighting and natural building stack effects).
  5. Swab and tape samples for cultures may collect the wrong mold. Swab or tape samples used for culture for identification of what's on a surface have the same viable-non-viable question We have already raised. Everything depends on where you collected the swab or tape sample.

    Moving a tape or swab over as little as one inch on a surface, and certainly moving it a few feet, can collect a completely different mold genera and species! An "expert" should know what's probably representative of the building and should know where the important genera/species are likely to be growing. Many investigators are quick to sample the highly-visible "black" mold on a surface and under-sample very important but hard to see light colored molds often found higher on a wall, for example, where the surface was less wet.
  6. Cultures are probably not really being done with full accuracy in some labs, especially for Aspergillus: Culturing on one or even two media risks that the important genera/species in the sample does not grow at all on the medium, that it grows in a different form and is identified differently than it appears in the building, or that it is overgrown by another genera/species present which likes the culture more than the target species.

    We have demonstrated this culture-media variation in a study we am pursuing about mold in tea. In a problem-tea sample cultured on the most commonly used culture media, MEA, the culture produced an overwhelming growth of Cladosporium sp., while a parallel culture (from the identical sample) made on DG-18 produced a single Cladosporium colony and grew an overwhelming collection of Aspergillus niger!
  7. Non-viable spores, that don't grow on culture may still be toxic or allergenic particles which are a problem for some people exposed to them.

While we enjoy growing mold cultures in our lab (it makes for nice, photogenic mold colonies), it is less often useful than direct microscopic examination of a field-collected surface or vacuum sample.

Without the added step of mold culturing, from a good surface sample using adhesive tape, a trained microscopist can identify mold genera and mold species as well in many cases. In many instances, knowing the mold genera is enough to decide on a course of cleanup action without further expense.

For example, if we agree that there are no harmless Aspergillus species or Penicillium species that grow indoors, then for purposes of deciding on the need for remediation, only the size of the reservoir is important. P. notatum, used for making the drug Penicillin, has not to our knowledge been found growing on building materials.

For more discussion about mold cultures from settlement plates or swabs see "The Validity of Cultures at

Comments on the Validity of Swab Sample Tests for mold

Swab samples can be used to pull particles for microscopic exam but destroy the identifying conidiophores and hyphae; They are more often used to prepare cultures which have the shortcoming cited above. We make use of swabs to sample for bacteriological contamination.

A sterile swab is wiped across a sampled surface, the inserted into a sterile tube for mailing to a lab.
Swabs are processed in one of two ways:

  1. Direct examination: The lab can lift particles from the swab using tape or other methods to make a direct particle examination similar to tape sampling above.
  2. Culturing: The lab rolls the swab across a culture plate to culture the sample for identification.

Shortcomings of swab sampling for mold

  1. Direct examination: determination of species by direct examination is nearly impossible as the collection method destroys or fails to collect identifying structures such as conidiophores and hyphae. "Rubbing" and possibly even "rolling" the swab on a surface to collect a sample will often destroy key structural components (the conidiophores and hyphal details) which would have been more easily preserved using adhesive tape.
  2. Culturing from swabs (or tape): risks misidentification of the dominant species present and may completely miss species which are present due to choice of culture media and growing conditions, as stated above about mold cultures.
  3. Swabs used to collect particles from insulation, fabric, upholstery, carpets, may fail to collect representative material as they only touch surface particles. Vacuuming such surfaces is more representative of what particles are aerosolized by human activity in a building.

Swabs are great for testing for bacteriological contamination testing but in our opinion they are of less use in fungal work.

Comments on the Validity of PCR methods for mold Identification

Polymerase chain reaction (PCR) can be used to identify individual genera/species with good accuracy and fairly quickly. The method requires costly equipment and is not available at most laboratories. Perhaps more important is that the data base of PCR identification information is limited to a small set of species compared with the wide range of genera/species which occur.

At least one excellent national laboratory offers this service for mold speciation. Depending on how rapidly technology drives down the cost and how rapidly the identification data base is expanded, I suspect that this method will see increased use.

The limitations of PCR tests for mol dl are currently two:

  1. first, it is quite costly to perform per sample, and
  2. second, it is excellent at identifying the presence or absence of a specific mold you're looking for.

PCR mold screening is less useful as a broad spectrum scan expected to pop up with a result of what's present out of the 1.5 million possible candidates - of which only a few are yet even in the PCR database.

The Usefulness of mold Testing vs. Mold Identification

Are mold Home Test Kits Useful? Accurate? Worth the cost?

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 at The Validity of Cultures.

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;

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 I 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.

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. Cultures whether from a "home test kit" culture plate or a swab are unreliable as a characterization of presence or absence of mold because first, only about 10% of all of the 1.5 million mold species on earth will grow in any culture under any condition, second because what grows on a particular culture may be what likes that culture not what is the dominant problem, and third, 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 I'm 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; third, the location(s) of the problem reservoir; 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 building areas without testing for mold

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 "When to hire a professional" for more detailed help in deciding when and how to proceed.

When is it useful to identify mold?

See MOLD / ENVIRONMENTAL EXPERT, HIRE ? for a discussion of when it is or is not appropriate, justified, and ethical to hire a mold consultant to inspect, diagnose, and advise about mold contamination in a building.

Why try to identify mold at all? Some practitioners argue that no testing is needed, mold should simply be found and cleaned-up. We agree with this approach for small areas of mold where there are no larger issues such as occupant complaints or BRI (Building related illness).

Why identify mold - Reason 1: Cosmetic-only vs. problematic mold

but if mold present in the building is only of "cosmetic" concern, it is unlikely that special cleanup methods such as negative air, establishment of a containment system, and special personal protection for workers is needed. If these special methods can be avoided, the cost to remove mold will be substantially less.

Therefore it cases where a large amount of mold is present it may be appropriate to have an expert perform testing and to prepare an appropriate remediation plan to guide the remediation contractor. The same expert may be used to perform clearance testing later to assure that the cleanup was proper and successful. Also see Can mold make you sick?"

Harmless "Black mold": A very common example is the Ceratocystis/Ophistoma group which appear as "black mold" on framing lumber and which are more commonly known as "blue stain" or sapstain molds. This mold is found on lumber as it arrives from the lumber yard - a condition that is readily apparent to a building expert and which can be confirmed by sample identification.

Allergenic mold: Other dark molds, including the most common genera Cladosporium sp. are often allergenic: a potential respiratory irritant or a problem for people with allergies, asthma, or other sensitivities.

Toxic/Pathogenic mold: a third broad group are molds which we call "toxic" and includes species which are toxic, pathogens, or infectious agents which in some cases may be capable of infecting humans or of producing disease in humans. Aspergillus flavus, A. niger, are two examples.

We find in many cases that large areas of "black mold," about which owners/occupants may be unduly frightened, are Ceratocystis/Ophistoma, a common mold that is found on framing lumber from time of construction, and which is known to be only of cosmetic concern, and which is not an indicator of mold-conducive conditions in the building - it came in on the lumber and is inactive and cosmetic.

Without knowing what this is, people may make large and inappropriate expenditure on "professional remediation" - in one case in CT a client was about to launch a $600,000. complete re-framing of the first floor of a building, a totally inappropriate step which was completely unnecessary with a little knowledge of mycology and building science.

Ambiguous airborne mold counts: A second example of this sort is the need to distinguish between two "mold counts" that appear to be the same but actually mean very different things. An outdoor 500 Pen/Asp spores/M3 of air and an apparently low indoor 400 Pen/Asp spores/M3 may take on a new meaning if the outdoor spores are a different genera/species than the indoor ones.

Why identify mold - Reason 2

Proving that mold in a building caused a health concern is so arduous and costly as to be inappropriate in most cases. If a lot of allergenic or toxic mold is present, it needs to be removed. but information about what was found in a building may be useful: a number of our clients have health complaints for which IAQ problems are a potential cause or contributor - information which they want to convey to their physician.

For example, a delay in diagnosing fungal infections in two of our clients led each to have permanent loss of eyesight. We acknowledge that these cases are not common, but they occur enough for caution to be in order. We don't submit that we should be practicing medicine nor diagnosing ailments, rather that information about a sick person's environment might be useful to their physician.

Dr. Harriet burge at the Harvard School of Public Health (HSPH) has taught us that the cost of proving that a specific illness is caused by a specific mold or allergen in a particular environment is so arduous as to be impractical. However we agree, as we expect you do too, that if a large area of allergenic or more toxic mold is present in an environment it should be removed.

Can mold Make You Sick? We live in a sea of mold, and other stuff in the air we breathe, on cushions we sit on, clothes we wear, pools we swim-in, and so on. Most mold is not hurting anyone, and some of it makes us well when we're sick(Penicillium notatum, for example).

Fear of mold (mycophobia) is usually unjustified and in our opinion, more a result of media hype, enviro-scare, and gouging consumers. A healthy person walking through a room of moldy air is not likely to die. On the other hand, there is a wealth of less rigorous empirical data matching occupant complaints with indoor mold and allergens.

Finally, for certain people, mold can be a serious problem if it's at high levels indoors. It's probably an overstatement by those authorities who assert that "... there are no proven links between mold and illness." we refer readers to some of our lab's references for descriptions of illness-related molds, some of which are found in buildings:

  1. Identifying Filamentous Fungi, A Clinical Laboratory Handbook, Guy St-Germain, Richard Summerbell, Star Publishing, 1996, ISBN 0-89863-177-7 (English)
  2. Fundamentals of Diagnostic Mycology, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6
  3. Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon) - The Atlas of Clinical Fungi is also available on CD ROM
  4. contains a more extensive reference list.

Why Identify mold - Reason 3: establish a data baseline and later, evaluate the success of a professional mold remediation project.

See mold EXPERT, WHEN TO HIRE for a discussion of when it is or is not appropriate, justified, and ethical to hire a mold consultant to inspect, diagnose, and advise about mold contamination in a building.

Where large areas of remediation are needed, using professional cleaning services, we find that in many cases the "professional" does not properly maintain containment, and actually increases the level of allergens in the building. In buildings where occupants are at particular risk (elderly, immune-impaired, infant, asthmatic) We have had cases where an occupant entered an area contaminated with high levels of allergenic mold and suffer severe asthma attacks. In Ellenville, NY we are aware of a fatality involving just such an instance.

For large remediation projects we find it very useful to have a base-line of data on what areas need to be cleaned and which are acceptably clean before the remediation project. Then a quick test after the remediation can confirm not only that it was successful, but that the remediator did not inadvertently fail to contain.

If the containment was unsuccessful and other building areas have become contaminated enough to want to have additional cleaning (typically HEPA vacuuming or wiping), having the baseline showing that the contamination followed the remediation rather than preceded it protects the property owner or occupant from additional unnecessary expense.

The usefulness of samples depends on the knowledge and thoroughness of the person collecting the sample as part of a building investigation. Arbitrary or random samples are unlikely to be a reliable characterization of a building. Choice of method as well as how the method is applied (for example, just where to stick the tape to collect a surface sample) makes a large difference in the quality and representativeness of the sample.

Articles on Mold Testing Procedures, Validity, Reporting

Following this list of mold testing articles we include the text of a lengthy discussion of various mold inspection and test methods in popular use.

See mold Sampling Methods in the Indoor Environment and in addition, the mold test critique articles listed just below.

Readers should also see TECHNICAL & LAB PROCEDURES.

MOLD TEST KITS - Home Test Kits for black or "Toxic" mold using Clear Scotch Tape: bulk & Surface Sampling Protocols for mold Testing

This expert-recommended mold test kit is cheap and yet
top performing *IF* you use a competent analysis laboratory!

Mold Test "Kits" Using Adhesive Tape - useful for almost any sort of dust or particle collection & forensic analysis

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to a lab - we like it much better than the mold culture plate shown above.

Bulk Sample Mold Test Procedures

Mold Testing: bulk or Tape Surface Samples and their interpretation - a quick tutorial A brief introduction to using adhesive tape to collect particle samples such as from mold-covered surfaces; scrapes onto microscope slide and other methods also used by do-it-yourselfers and by experts

Vacuum Sample for Mold: testing carpets, insulation, draperies, couches, wall cavities

Vacuum Samples of building Cavities: Wall Check™ type vacuum pump and canister permits "sampling" of mold and allergens in wall, ceiling, and floor cavities but our direct field testing indicates that this method is highly unreliable.

Working with Louis Relle, a Louisiana mold remediation expert on a New Orleans building which was to be demolished we collected wall-check samples from every suspect building cavity.

When the building interior surfaces were demolished we then performed a visual inspection and collected bulk surface samples using tape.The wall check samples were completely unable to detect large and significant mold contamination in the cavities of this building.

We postulate that even with mechanical agitation (banging on the wall during wall check sampling) the flow rate of the sampling method does not move enough air to reliably pick up surface contamination unless the mold genera/species happens to be at a particularly high state of active sporulation. The tool remains in the professional's arsenal, to be used with discretion.

Vacuum samples of Soft Goods of carpeting, drapes, furniture, clothing permits testing for mold contamination. We use this method for screening of areas where mold is not visible, and in clearance testing.

MOLD CULTURES - Validity and Usefulness of mold Cultures & Culture-Based Home Test Kits for mold

Mold Test Kits Using Culture Media

mold culture (C) Daniel Friedman

Useful, inexpensive tools which are reliable for characterization of building conditions include the adhesive tape method described below.

Questions about the validity of alternative "home test kits" based on mold cultures are discussed below. Questions about and limitations of air tests and virtually every other mold testing method are discussed at our in-depth
"Mold Sampling Methods" article.

How to Send A mold Sample to Our Lab: 6 Easy Steps for a mold Test: How to Collect mold Samples Using Adhesive Tape and Plastic bags - a low-cost high-quality and very easy method to send a mold sample to a mold laboratory for analysis

For a quick to understand overview of the validity and usefulness or perhaps not-usefulness of culture tests for mold,
see Validity of Cultures (settlement plates or swabs) to find toxic mold in buildings which is an overview and critique of using mold cultures, settlement plates, petri dishes, and cultured swab samples, and air sample testing limitations for determining what's in a building, and which tests are useful in different situations.

For more thorough detail see Shortcomings of cultured mold samples which lists a number of detailed concerns about viable spore traps and culture media for building problem detection

TECHNICAL PROCEDURES - Technical & Laboratory Procedures for Mold Testing

Good Laboratory and Microscope Procedures are critical in making sense of field samples. Competent, trained, experienced aerobiologists, mycologists, and microbiologists can identify sample contents with good accuracy.

Depending on the experience of the laboratory, it is also possible to interpret the meaning of the sample for the building and its occupants. Laboratory professionals who have also performed the field inspection can make useful extrapolations from lab results. Hasty work by disinterested parties may be less useful for building occupants and owners.

Please see TECHNICAL & LAB PROCEDURES for the full text article on this topic.


Continue reading at ACCURACY OF VARIOUS MOLD TEST METHODS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.








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