7 Reasons Why Mold Experts Don't Use Plate Testing
By PJ Harlow, Holistic Mold Consultant
8.5 Minute Read
When you’re just starting to explore the possibility of mold in your home, petri-dish, mold plate tests are one of the first things that come up in your Amazon search. They are also frequently recommended by maintenance and local contractors as they appear to be a reasonable (and cheap) start to find answers. Right?
As seasoned Holistic Mold Consultants, my co-founder Peter Harlow and I are commonly approached by health-conscientious homeowners, renters and even mold sick clients who ask,
“Is petri-dish plate testing a good method to test for mold in my home?”
The answer depends on what exactly you’re hoping to get as a result but as experts in the field of mold, it’s not something we would recommend to clients for real answers. Before I explain, let’s look at why so many people turn to this style of testing in the first place.
Affordability
The #1 reason people turn to petri-dish, mold plate tests is because they are the least expensive, at-home mold testing method on the market. Plain and simple.
Since “Fundamentals of Home Health”is not a topic in high school, nor is it a college course, or a subject that the average homeowner is prompted to master, most people have no idea how to maintain their home’s biological health, let alone the chemistry & physics involved. Due to this global lack of knowledge, it would be rare for a person to have a baseline average expectation of what one would commonly invest into indoor home mold testing. The mindset is usually, why spend a few hundred dollars on an ERMI Test when you can do a plate test for under $40 bucks?
Easy to Do, Easy to Obtain
Plate tests do all the work for you.
They are widely available online, on Amazon, and locally in places like Lowes and Home Depot. As a regular go-to recommendation from practitioners, contractors, plumbers, HVAC techs and other general building-industry types, it’s a simple way to produce a very visible outcome.
Question is, does that visible outcome provide the answers you’re looking for? Probably not.
7 Weaknesses of Plate Testing
1. Spores Grow
Mold spores are like the seeds of a mold colony.
They are ubiquitous, and believe it or not, they are a natural part of our world.
When we talk about a healthy home, there is no such thing as a “mold-free” home.
In fact, you will never be able to 100% prevent the opportunity for mold to grow in your home.
If you are part of my online community, you know I try hard not to speak in absolutes (every, always, only, etc.), but realistically, this is a critical concept to master and an important aspect of the launguage we use.
So often I hear people use language in this community that is more colloquial than actually true. This topic is a perfect example. When I hear folks say, “I want to build a mold free home” without batting an eye.
I know that It just kind of pops out before they really had a chance to think about the meaning of what those words imply. While it would be nice to assume that everyone knows that’s not actually true, a lot of people don’t. And it’s verbiage like that which confuses people when they are setting expectations.
If you are diving head first into this convoluted and complicated community, the idea that you can prevent mold or bacterial growth within the fastest evolving biome in the world is not only a very audacious but as a scientist, educator and avid health advocate, I would ask, why would you want to?
You’re probably thinking, “Geez, what’s this woman smoking? Is she crazy? Does she want mold?”
Stick with me, I promise I’m not crazy.
We aren’t made to live in sterile homes.
Mold is part of the life cycle of our world. Its job is to recycle and break down organic materials. If we don’t have water damage, and if we work to control the vapor/moisture & humidity in our homes (as well as some other factors), we can live in harmony with mold, both in and outside of a building.
When you intentionally provide an attractive, petri dish garden filled with yummy mold food for spores to propagate & grow indoors, it will absolutely do what you ask of it. That is the thing with plate tests, you can always expect mold spores to grow on a plate unless you’re in some type of a pharmaceutical clean room.
2. Shock Factor
As we kind of uncovered in #1, Petri-dish plate tests are made to intently grow mold.
If a person is unaware that mold spores are everywhere, it creates some confusion if the expectation of a “good” test result is no growth, and on the contrary, a sense of shock ensues when the a “bad” result appears in the presentation of growth.
Petri Dish testing should be used more as a 2nd grade science experiment rather than a method to measure actual indoor/home mold risk exposures, since it's always going to grow something. Fungi is one of those things that mother earth created to be omnipresent, so when something organic dies, and needs to be “broken down” and brought back to the earth, mold arrives-- right on schedule.
In our homes however, if we have water damage, high humidity, condensation &/or moisture intrusion somewhere, mold mistakenly thinks we want it to do its “work”. It doesn’t understand this is your house. It’s just doing its biologically engrained job.
3. There is more to mold than just spores
One of the bigger obstacles regarding mainstream beliefs around mold, (especially within the traditional mold industry) is the constant sole-focus on just mold spores.
Mold spores account for only one small part of a mold colony.
Kind of like the acorns to a tree. If we were searching for trees in your house, can you imagine how limited our chances would be if our only evidence was to allow acorns to grown in a garden? That eliminates a huge portion of the primary by-products of growth!
When you walk into a forest, what do you see on the forest floor? Evidence of trees growing through the seasons and rebirth. You see leaves, branches, twigs, bark or any other parts of the tree as well. This is the same for mold just on a micro level that we don’t see. Do you see the conundrum here?
Mold spores are also not the only part of mold that can affect human health, nor the only part that factors into a sick building with sick or symptomatic occupants. Don’t get me wrong, I am not saying plate tests are totally useless. You may be able to pick up an elevation if you’re right near a source and the air pressure is just right, but, you’d have to do multiple room by room tests all over the house to get a baseline first, which, after calculating the costs, you could invest that into better testing & a more informed start that could provide you substantial evidence, confidence in what you’re doing, and more useful parameters.
4. What about dead mold spores?
When we focus solely on viable mold spores, we leave out the DRY, OLD &/or DEAD mold in a house, we leave out the mycelium and hyphae, (similar to roots & branches on a tree), and we completely ignore the quantification of fungal fragments of a colony.
These sub-micron size fragments and particulates can be especially dangerous to your health, being our bodies natural defense mechanisms don’t pick them up due to their undetectable micro-sizes. The health risk grows exponentially with the knowing that these fragments aerosolize up to 320x’s higher than spores within our indoor air.
Plate testing ignores these health risks. So does air testing.
5. Heavy Spores
Water-loving molds like Stachybotrys (Black mold) & Chaetomium have a high water activity level, needing substantial levels of moisture, and more time to grow compared to drier, primary colonizers molds like Aspergillus Ochraceus, Aspergillus Niger, and Aspergillus Restrictus.
Stachybotrys spores are also stickier, heavier, & not easily aerosolized (airborne). The likelihood of these spores being suspended in our air for notable periods is very low, so this equates to another con as to why plate tests remain unreliable when it comes to measuring any kind of mold-related health risk in a home.
6. Competitive Spores
As giants living in an invisible micro-universe, we often forget that fungi & molds are living microorganisms. Even though we don’t fully understand or regularly recognize their fascinating and transcendent purpose, their lives are just as active and important as our own. We just don’t see it.
Molds are constantly competing with other molds, yeasts and bacterias. It’s a war that has been waging since the dawn of time. They all want to be “king of the castle”, and will use their very powerful defense mechanisms to help them dominate in an area that is alluring terrain.
Interestingly enough, some molds that are highly debilitating and dangerous to humans, are weak when forced to challenge other molds in such a small environment like a petri-dish. This element alone can create an overgrowth of a more dominant species, preventing the realistic presentation of diversity that is actually thriving and present inside the microbiome of a building.
7. Variable Spores
Spore concentrations in a home can vary by the room, because of the air flow or human & mechanical activity, by the ventilation, by the climate, season & weather conditions, by the time of day and even vary by floor, height and position within a dwelling.
All of these variables & metrics make it difficult to gather a proper historical or realistic glimpse of human spore exposures (inhalation) since the spores are not uniformly distributed in the air.
Due to this, Petri-dish plate samples will also produce extremely skewed results as well.
What test do I start with?
A: If your focus is health, and your concern is water damage, mold, or even mycotoxins, we recommend starting with the ERMI Test.
This is a comprehensive dust test used to gauge the level of water damage molds, and conversely the level common indoor molds within your home or selected space. The ERMI can provide us with a starting baseline of data to begin measuring if your home has a mold issue.
The ERMI can also help us to answer some of these more common questions*:
Does my home have a mold problem?
Are there elevations of harmful molds in my home that could be affecting my health?
If so, what species and how much?
Is my home risky or safe?
Do I need an inspection and what step do I take next?
*It’s realistic to recognize that petri-dish plate testing will NOT give these answers alone.
Of all the available tests out there, we recommend starting with the ERMI test as an initial screening for anyone starting out.
Q: CAN I READ THE ERMI TEST RESULTS MYSELF?
A: Maybe, but normally— NO.
You might be able to recognize a high result, or even get some stats on the internet, but actually interpreting the results & patterns within an ERMI Test requires knowledge of each species, common health effects, notable behaviors, typical growth locations and a trained eye. This is in addition to doing an intake with the occupants of the home.
The ERMI is a sophisticated, professional-grade, environmental dust test that is both extremely comprehensive and complex. While sampling dust for the test is easy to obtain with directions, the results are not easy to decipher for those who aren’t professionally educated & trained in Microbiology, Indoor Air Quality, MSQPCR laboratory testing and some aspect of Environmental Medicine.
We highly recommend getting the most valuable information from your ERMI and consider working with PJ. She was the very first pioneering, virtual consultant to begin offering ERMI Interpretations Online.