5 min read

Mold Testing Methods

Published on
May 18, 2023

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I am often asked about mold testing and specifically, what is the best way to test for mold. The answer is multifaceted and a little complicated. First of all, there are multiple ways of testing for mold, all with their own set of pros and cons. Among them are:

1. non-viable spore trap tests

2. Viable spore trap tests

3. Tape pull surface testing

4. Big box store home test Petri dishes

5. Swab tests

6. Anderson Sampling like tests

7. ERMI or HERTSMI testing

8. Particle counter testing

And this is just a partial list, more and more are being invented and marketed. The reason for this? None are great, and not one of these can give you a “definitive” answer whether or not you have elevated “mold load” in your home.

To break down the pros and cons of each method let's first consider spore trap tests. Spore Traps are small cassettes that are attached to an air pump. Industry-standard calls for the pump set at 15 liters per minute, and to run the pump for 5 minutes. This pulls in 75 liters of air. What is it pulling in and “trapping”? All particulates that it can within a small area, within a room, within a home, at a particular time of day. All of these are variables. Additionally, mold is in 1 of 3 conditions at all times. Either sporing, growing, or dormant. Spore traps are the only test for sporing. I repeat, it only tests spores floating in the air. So in a nutshell, we are testing a small area of one room, for 5 minutes looking for 1/3 of the states of mold.

I have been in bathrooms in which I can see the mold growing on a wall, and the test comes back relatively clean. Why? That mold is not stressed. It’s getting moisture from daily showering, it has food, and it's happy. It’s not going to spore unless it gets stressed. So spore traps have their inherent limitations. Whether we are talking viable or non-viable, the same limitations apply. The only difference is that non-viable tests are optical readings under a microscope at the lab, and viable is actually grown by the lab.

Next is Tape pull tests. These are useful for situations in which you think that weird looking stuff on the wood trim, or around the toilet, etc, may be mold but you are just not sure. The tape is pressed against the substance in question, and the lab will optically identify it as mold, and specifically what kind. This does not, however, quantify the mold load of a home. The report will give you a 1-4 score, so as an example, Aspergillus, with a 1, simply means “there's a little bit of aspergillus on that tape” to a 4 meaning, “there's a bunch of aspergillus on that tape”. Basically useless information with just too many variables in play.

Big box store Petri dishes are one of the biggest wastes of money out there in the industry. The air we breathe has mold, it's part of our planet. What you don't want, however, is to have an elevated mold load in your home. By placing a petri dish out in your home, you are determining absolutely nothing. Mold is in the outdoor air, outdoor air comes indoors, it’s a bad test. Perhaps if you could identify a “marker mold” i.e. Stachybotrys, or chromium it is of some value, however, people often just look at the mold grown in the dish and panic. Mold is part of life, Elevated out of control mold should not be. Petri dishes will not distinguish whether it is normal everyday mold count or out of control mold load in the home.

Swab tests are like a tape pull test in that you will test a very small surface to determine if it is mold and what type it is. It is more commonly used for bacteria testing, however, some use it for mold testing. It will distinguish between live mold and dead mold, which a tape pull test cannot. The lab will take the swabs and “grow” whatever is collected in the swab. Again, this cannot quantify the mold load of a home. It's more for identifying whatever is on a surface.

Anderson Sampling, or Cascade Impactors. These are the genesis of spore trap testing. They come in a number of stages of aluminum plates, or dishes, which have smaller and smaller holes as the air continues through the plates. It utilizes a pump to pull the air through the individual stacked filters. This, in effect, filters out the particulates by size, and the end result of the last plate is often incubated much like a “via-cell” spore trap cassette. This is likely more accurate than the more commonly used plastic spore traps but is also more cumbersome, and prone to cross-contamination from one testing site to another. Again, with the cascade impaction, you are testing for 1/3 of the mold and this is in a small area, within a home during a small 5-minute cycle.

ERMI testing stands for the Environmental relative moldiness index. It was a test originally developed in an attempt to establish a baseline for healthy vs. unhealthy homes. The test “scores” the home, with a range of above 10 unhealthy, and below 10 considered healthy. The test involves vacuuming or dusting up a 10 foot by 10-foot area of flooring. This dust is then submitted to a lab that breaks the mold down to the actual DNA of the mold. This test, since it could be picking up dust from years in the past, is a very good test for determining the mold load of the home. Particularly the mold history of the home. What has happened over the years and accumulated to this point. The cons of the test are that it is very expensive, and probably gives the customer more information than is needed. From strictly a Pure Maintenance standpoint, the treatment we offer is going to take care of the mold, regardless of its family or genus. The drawback of this test, from a Pure Maintenance standpoint, is that through the use of polymerase chain reaction testing, it results in the actual DNA being identified. So even though our process oxidizes and destroys all spores and cells, the DNA still remains. For this reason, the ERMI is good before the test, in which they score the healthiness of a home, however, it is not a good test at determining the efficacy of our treatment. The now harmless DNA will always remain. Even after treatment. There are a number of health practitioners who understand this dynamic, and still recommend Pure Maintenance to their patients. The ultimate test, obviously, is the health improvement of their patient.

And finally, particle counting has been a recent addition to the mold testing world. Particle testing or counting uses an advanced method involving lasers providing an intense light and thereby counting very small particles and grouping the counts by size. Again, the inherent problem with this type of testing is that mold is not always sporing, so it is not a great test for determining the overall mold load of a home. It is, however, good at counting particles or particulates and grouping them in a range roughly the same size as most mold spores. The advantage of this test is it is in real-time. This test method accurately assumes most molds are in a similar range of sizes.

Overall, testing for “mold load” is not a perfect science, and may never be a perfect science. However, what is close to perfect, is the Pure Maintenance method of reducing the “mold load” in a home, as evidenced by thousands of happy customers.