How mold grows within 24-48 hours in a wet building–even if you can’t see it

By: Lee Ann Billings

Ten tips to avoid structural mold from flooding

In wet buildings, mold will begin to grow within 24-48 hours. The wet building materials act as “food” to sustain the mold, many of which are toxigenic that flourish in wet buildings. In addition to mycotoxins (mold poisons), bacteria that result in bacterial toxins also grow, creating complex indoor environments of microorganisms, toxins, and volatile organic compounds (VOCs).

A few simple steps can save property owners thousands of dollars of damage due to structural mold growth. – Doug Hoffman, executive director of NORMI

The National Organization of Remediators and Microbial Inspectors (NORMI) is a not-for-profit trade organization that certifies indoor air quality professionals, including both mold assessors and mold remediators.

A Toxic Soup

When these molds and bacteria and their respective toxins get condensed in an indoor environment is when they can become harmful to the health of humans, especially those in high-risk groups.

“Taking the necessary steps to avoid structural mold growth will not only preserve the integrity of a structure but also the health of its occupants,” explains Lee Ann Billings, co-author of the book MOLD: The War Within, which details lessons learned from Hurricane Katrina, as well as her family’s journey of recovery from mold illness.

Where to start?

Hoffman instructs, to minimize structural mold damage and risk to health, it is imperative for flooding area residents to be proactive, act quickly, use proper personal protection equipment, and implement the following ten steps:

  1. Remove any standing water using a pump or a wet vac. If the water damage is from a broken pipe, be sure to turn off the water supply.
  2. Remove wet carpets, rugs, draperies, and personal belongings. Clear mud and debris from floors and foundation walls to allow the subflooring and foundation to dry.
  3. Remove and discard water-saturated sheetrock and insulation 18 inches above the highest watermark to increase structural drying. Remove water-damaged flexible ductwork and water-damaged insulation around metal ductwork.
  4. Remove all mold growth on remaining structural building materials by mechanical means or complete removal of the building material, if necessary. The easiest and most effective way to initially clean mold from structural building materials is to use a commercial wet/dry HEPA vacuum, followed by wiping, scrubbing, scrapping, or sanding for complete removal.
  5. Don’t use bleach to clean mold. Bleach is an effective sanitizer, but it will not remove mold at its “root”. The mold will look like it’s gone but it’s not—it will only grow back.
  6. Use sanitizers on any portion of the structure contaminated by sewage or flood waters.
  7. Dry the structure out as quickly as possible as structural mold begins to form in the first 24-48 hours. As soon as the above removal steps are completed, turn up the heat, circulate the air with fans, and use a dehumidifier to keep the indoor humidity below 50 percent. Hot, dry air dries building materials faster than cold moist air. If there’s no electricity, open windows and doors to get air moving to speed up the drying process, weather permitting.
  8. Check the attic as undetected roof leaks can later cause structural mold problems.
  9. Inspect windows on the outside of the structure, checking for damaged caulking and seals that could lead to future water leaks.
  10. Don’t seal it up until it’s dry. Siding, sheetrock, and flooring repairs should be done only after the substrates are completely dry. Confirm moisture content by using a moisture meter calibrated correctly for each type of building material.

For more information

For additional information from experts in science, medicine, and industry on structural mold, the health effects of mold and chemical exposures, and natural treatment options, see the book MOLD: The War Within, which also contains research from published peer-reviewed documentation. The content in the book is for informational purposes; so please consult with a licensed medical professional and mold professional based on your individual situation.

To locate a NORMI certified mold professional, see the location-searchable database on, which details licensing status and active certifications of NORMI members.

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