What I Consider a Mold Activity: The Primer

Clients frequently ask us, “How are you able to find mold problems when I don’t see anything and neither does anybody else.” Or a common variation on this theme, “I have a mold test but I don’t know what it means.” Our answer is, we follow the Sherlock Holmes investigative approach that has been described in virtually all of the published standards.

What does this mean? It means that you look for clues, which means you are looking for data. And you can’t really evaluate data unless you understand what it signifies. You need some basic understanding of the critter you are pursuing. Let us start at the beginning.

What is Mold?

As we all know, mold is a family in the Fungi Kingdom. The fungi have been around for billions of years, predating humans by a long shot. They are naturally occurring and play vital roles in nature. The fungi are one of very few creatures that can directly digest cellulose. If it were not for the fungi, we would be up to our eyelids in tree trunks, branches and leaves. The fungal digestion of these materials provides the organic matter that makes soils fertile and productive. Their presence in nature is absolutely essential to the function of life systems as we know them.

We just don’t want them growing inside our homes.

What does Mold Need?

Like all life forms, mold has three fundamental needs: proper temperature, food and moisture.

    • Temperature: The temperature range required by mold is generally in the 40-105o F range. Of course, this temperature range is pretty much a given inside our buildings.
    • Food: In nature, the food is comprised of the many cellulose based materials, mostly from plants. In our buildings, however, the three main food groups are drywall, carpet and fiberglass insulation. Drywall because of the paper liner, which is simply pre-digested cellulose. Carpet because of the synthetic chemicals, mainly petroleum based, from which it is made. And fiberglass? Well, mold cannot eat glass, which is entirely mineral, but it sure likes the adhesive that is used to form the insulation into batts. So let’s face it, there is plenty of mold food in our buildings.
    • Moisture: Given the above, it is clear that moisture is the limiting factor. If we can control moisture then we can control mold. When there is a liquid moisture release, such as from a plumbing leak, window leak or flood, mold will grow if the affected materials are not dried in a hurry. The smart people give us about 48 hours to get dry. So get busy after that pipe break.

But mold does not need liquid moisture. Liquid moisture is essentially 100% relative humidity, like when water condenses on your air conditioning coil because it has reached the dew point. But some molds will grow fine at about 75% moisture activity, which is well short of liquid water. This is why we often focus our attention on spaces where there may not be liquid water but where the relative humidity reaches above 75%. The two most famous spaces where this can routinely occur are basements and crawlspaces. You have to look down there.