Tips & Tricks/01.25.23

What Makes Mold Grow?

Airborne mold spores need a proper "home" to reproduce. That location must provide: food, water, a calm environment, preferably darkness (however mold can and does grow in lighted areas), and an acceptable temperature.

Of those factors, water (moisture content) is the one that we can best control to limit the risk of mold growth.

How Wet Is Too Wet?

The percentage of moisture content is defined as the amount of moisture in a material compared to its oven-dried weight. Thus if a piece of wood weighs 100 lbs., and has a 10% MC (moisture content), then 10% of that weight, 10 lbs., is water weight.

Key threshold moisture content (MC) levels for wood are:

  • 30% MC -  Wet rot occurs.
  •  20% MC - Mold growth accelerates. Certain molds, such as Stachybotrys chartarum, require high water activity to grow, which then leads to wood destroying “dry rot” fungi, and decay.
  • 16% MC - This is the lower limit of moisture that will support mold growth. Thus if the MC can be brought below 16%, not enough moisture is available to support mold growth.

How Fast Does Mold Grow?

The two molds most commonly found in remediation work are Penicillium and Aspergillus, both of which can form a colony (colonize) within 48 to 72 hours. Their spores are respirable, meaning the mold spores can be drawn into the lungs during normal breathing.

Both Penicillium and Aspergillus are xerophilic, which means they can grow in low moisture environments; however, both still require a moisture content (MC) of at least 16%.

What's the Best Way to Prevent Mold Growth?

To prevent the conditions that foster mold growth, it's critical to remove bulk water then dry materials and reduce humidity as quickly as possible with Dri-Eaz low-grain refrigerant dehumidifiers (LGR 7000XLi, LGR 6000Li and Revolution LGR) and high velocity airmovers (Velo and Velo Pro).

See more microbial remediation-related articles in Legend Brands Tips & Tricks. Want to become a certified Applied Microbial Remediation Technician? Check our Legend Brands Education class schedule for upcoming AMRT classes.


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