Mold Testing


Mold testing is not really required if the mold is highly visible, and there is no need to know the type of mold that is growing.  However, testing should probably be done if it appears that pets or people have been exposed to mold and the source is not apparent or the need to know the specific type of mold is required for medical reasons.

Most mold testing is done by trained professionals, but there are kits people can order for home testing.  In either case, the samples collected are normally sent to a laboratory for analysis.  In short, the individual gathering the samples rarely analyzes the samples.  Rather, in most cases, the samples are transported under chain of custody protocols to a licensed laboratory.


There are two main types of samples.  One involves attempts to collect viable samples that can be incubated and identified.  This method provides more information and can be important when the occupants of a property have had exposure to a potentially dangerous mold.

Incubation increases the turnaround time between collection and conclusions, but it is more accurate from the perspective of identification. Non-viable samples are easier to collect and can sometimes be almost immediately analyzed.

Viable Samples

There are two main methods for collecting viable samples.  One involves a moistened swab, something like a Q-tip, that is gently rolled on a suspect surface and inserted into a tube.

The other requires a piece of equipment, usually an Anderson 6, that sucks air onto a petri dish containing an agar.  For those with a need to know, there is a sort of pump, similar to what is used to force air into aquarium water.  A tube connects to a unit on a tripod that opens to permit the placing of the petri dish.  After exposure to the fine air currents, the agar is pitted and looks a bit like the surface of a golf ball.

Pros and Cons

If mold is visible, as with stachybotrys growing on a wall, the swab is probably adequate.

The method based on air sampling presupposes the spores are airborne.  Some molds are more mobile than other molds so a combination of methods yields more complete information.

Another advantage of this method is that samples of indoor and outdoor air can be compared and relative counts are possible.  These are measured in colony forming units and give some idea of the relative importance of the numbers.

Non-viable Samples

Testing for non-viable molds requires almost no investment on the part of the person conducting the tests.

Normally, tape is used and pressed against a suspect surface.  The samples are put into clean plastic bags and sent to the laboratory.  Transparent mailing labels are often used for this purpose.  The more sophisticated labels are preprinted with a target area for the sample.  They also have control numbers.  These labels are about the same size as a microscope slide and make the work at the laboratory very easy because of the target zone.

Another method, not as common, is to suck air onto a prepared slide, sort of a variation of the viable sampling method except that the stickiness on the slide makes the sample non-viable.

Pros and Cons

Tape lifts are inexpensive and quick, but they do not allow certain determinations to be made.  Sometimes, very similar species look more or less the same.  Nevertheless, these can be useful for clearance testing following remediation.

With tape lifts, no information on density is possible.  For instance, if a sample is taken on two surfaces, six inches apart, and the two results are radically different, one still does not have a clear sense of the magnitude of problem.

The method using a prepared slide has the same shortcomings in terms of identification, but since the method involves testing of airborne spores, comparisons of different rooms as well as indoor and outdoor air are possible.

Issues to Consider

Every test has two costs: the time and labor of the person doing the tests and the laboratory charges.  More tests means more expense.  It could also result in more information.

The analysis of the laboratory results may also require interpretation, and there could be a separate charge for this.  This report may be generated by software or online surfing of the person writing the report.  It pays to ask how the report would be written because the laboratory results are just a print out of findings that do not have user-friendly language.

Contamination of Testing

In my opinion, a result that shows the presence of a particular mold is positive evidence of a problem.  The absence of such a finding can be almost meaningless because the sampling method may have been faulty or the handling of the samples did not meet industry standards or the laboratory itself could be inadequate.

As noted, with something like a tape lift, there can be extraordinary differences in results by just moving the tape a few inches one direction or the other.  Negative results therefore mean almost nothing whereas positive findings are definitely indicative of something requiring further attention.

Failure to culture something only means that the spores were not viable or the agar was not handled properly or something happened between the time of collection and incubation to inhibit the growth of the molds.   According to the National Association of Mold Professionals, laboratories are only 30% accurate.  This figure is used in comparison with mold dogs, specially trained dogs who sniff for mold, rather the gases produced by molds.  They have 97% accuracy rating.

The dogs are trained to point to the infected area.  That area is then inspected and samples are taken.  Someone wanting to determine how extensive mold contamination is can consider employing a tester who has a mold dog.  A dog is capable of inspecting an office building with 200 rooms in eight hours! 

Ethical Concerns

Mold, if found, requires remediation.  For an individual concerned about mold, it is extremely important that the person doing the testing can be trusted.  If the tester is also the remediator, he has a conflict of interest because recommending more work than is necessary is unethical.  Likewise, if the tester is motivated not to find something, one can be almost certain he can conduct the tests to produce this result.

Keep in mind that mold is microscopic.  Moreover, when magnified, a single slide possesses a simply enormous amount of information, often taking a long time to survey.  Targeting a single square with a piece of lift tape reduces the size of the sample to a manageable area, but eye strain and other factors can affect the examination of the slide.

For an individual concerned about health or property, it is important to have accurate tests.  For this reason, using a qualified, neutral person is the first step towards getting honest results.  Ask questions, get referrals, find out how much training the tester has, which laboratory he uses, and see if he really knows his subject.

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Notice:  The material on this site is based on the personal experiences and research of Ingrid Naiman, the site owner.  While every effort has been made to present accurate information, neither the site owner or web service provider claim the material will prevent or cure any medical condition, and no responsibility for the application of the information on this site is assumed by the any of the parties providing the content on this site.  None of the statements made on the site are intended to replace the services of health care or mold professionals.

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