DIY Mold Test Kits – Limitations of Settling Plates

While it may be tempting to use a do it yourself (DIY) mold test kit that utilizes settling plates to diagnose mold in a home or other type of building, this over-the-counter method often has many shortcomings.

Settling plates are petri dishes set out over a period of time to determine the presence of mold. The concept is that mold in the air will settle on the plates and begin to grow as the mold uses the agar in the petri dish as a food source. People are instructed to leave the plate out for a specific amount of time and then put the lid back on and monitor for any mold growth over specific time periods. If mold is found to be growing, the consumer then has the option to send the petri dish to a laboratory to have it analyzed, usually for an additional fee.

There are significant limitations to this type of testing, including the fact that some airborne mold is a natural part of the environment and can usually be found all around us. Other limitations may include:

  • No Expiration Dates – DIY mold test kits sit on hardware shelves or storage areas for undisclosed amounts of time and some kits may have no readily identifiable expiration date for the agar used in the petri dish.
  • No Air Flow Measurements – Most industry standards and guidelines report airborne mold samples as colony-forming units (CFU) per cubic meter of air, but determining a level of mold per volume of air is impossible without controlled airflow through the use of a mechanical pump.
  • Dead Spores – Settling plates are focused only on growing viable mold, but nonviable spores can also impact a person’s health.
  • Spore Characteristics – Different types of mold spores have unique weight, density and air flow characteristics and do not necessarily settle at the same rate. For example, heavier spores may settle on the petri dishes at a quicker rate during the specified sampling period and depending on the situation, some types of mold known as water damage indicators might not appear as readily using just this type of sampling method.
  • Additional Samples – Because mold is a natural part of the environment, additional samples are typically taken during a mold investigation from the outdoor air and from areas within the property that are not suspected of having a mold problem. This allows types and concentrations of mold to be evaluated, but many DIY kits do not offer additional sampling plates to make such comparisons.
  • Read the Packaging Carefully – Consumers may think that the DIY kit they just purchased will quantify and qualify the types of mold they have. With many of these kits there is an additional cost to have a sample analyzed by a laboratory.
  • Laboratory Inaccuracies – If the consumer chooses to have the sample analyzed by the laboratory mentioned in their kit instructions, how qualified is the laboratory and is it accredited by a recognized accrediting organization.
  • Shipping and Handling Issues – If the sample is sent to a laboratory, it can be subject to elements such as extreme temperatures and humidity, improper handling and overall shipping lag time. Such factors can contribute to false positives and false negatives.

Perhaps the greatest drawback to this type of mold test kit is there is no inspection by a qualified and experienced mold or indoor air quality professional. An inspection is a critical part of a mold investigation and often requires specialized instrumentation. In fact, the EPA states, “Sampling for mold should be conducted by professionals who have specific experience in designing mold sampling protocols, sampling methods, and interpreting results.”