What is Mold

Molds are organisms that are found both indoors and outdoors. They are part of the natural environment and play an important role in the environment. The term “mold” is a colloquial term for a group of filamentous fungi that are common on food or wet materials.

The majority of the molds that grow on damp building materials are found in the soil and are adapted to grow on a wide variety of materials. Different mold species are adapted to different moisture conditions ranging from very wet to just damp.

Mold primarily needs two important factors for growth, moisture and a food source. Building materials with a carbon base offer the food source, mold can grow on virtually any organic substance. Multiple sources of moisture exist indoors including water intrusion from outdoors, leaks and condensation on surfaces.

Elevated humidity (water vapor) in the air can supply enough moisture for mold growth.  Indoor relative humidity (RH) should be kept below 60 percent — ideally between 30 percent and 50 percent, if possible. Other factors for growth include substrate pH as well as micro and macro nutrients. Molds generally prefer a slightly acidic environment. Each mold species has a particular pH at which it grows best.

Mycologists (fungi scientists) refer to “water activity” when describing the required conditions for mold growth. The various species of mold have different water activity requirements. A material’s “water activity” is equivalent to the relative humidity of the air that would be in equilibrium with the material at that material moisture content. The vast majority of mold species require “water activity” levels that are equivalent to material equilibrium moisture contents corresponding to relative humidity’s of at least 70%.

Fungal spores behave differently in the air, some spores are smaller and lighter which get and remain airborne easily (Aspergillus/Penicillium sp.) while other spores are larger and heavier that do not remain airborne easily (Chaetomium sp. and Stachybotrys sp.). The fungal spore’s behavior can have an impact on how to remove fungal spores from the air. Understanding the behavior can increase the efficiency of passing post remediation clearance testing.