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Mold . . . A Growing Threat

Release date: 
July 26, 2004
Release Number: 

Sometimes the damage that occurs from flooding isn’t visible in the first days after floodwaters recede. Mold can be hidden behind the walls of a basement or in ductwork in a lower level. Disaster recovery officials warned residents of Milwaukee who experienced sewer backup and flooding from torrential rains in May, 2004, to thoroughly clean and completely dry areas that were wet to keep mold from growing into a health and safety problem.

Seventy-nine-year-old Ruth Collins had help from her neighbors to clean up the mess in her basement left after heavy rains caused problems with sewer backup in her neighborhood. But a few days after the neighbors were gone, she noticed black spots on her basement walls, including under her computer desk. The wet, humid conditions provided an optimum environment for mold growth.

During flood cleanup, you may think the air quality inside your home would be the least of your problems. But standing water and wet materials are a breeding ground for microorganisms, such as viruses, bacteria and mold. They can cause disease and allergic reactions and continue to damage the home and your health long after the flood.

Molds are fungi – simple microscopic organisms that thrive anywhere there is a moist environment. Molds can grow on wood products, ceiling tiles, wallboard, fabric, insulation and many other household and building materials. Mold growth can develop within 24-48 hours of water exposure, and will continue to grow until steps are taken to eliminate the source of moisture and effectively deal with the mold problem.

The most important points to remember in stopping mold growth are to eliminate the source of moisture and to thoroughly dry the area. Contaminated porous materials should be thrown out, such as bedding, rugs, curtains, books and paper. Hard surfaces should be cleaned with soap and water and then disinfected with a 10% bleach solution. If you are allergic to molds or the mold problem in your home is extensive, you may want to consult a professional cleaning service.

The black-spotted wallboard in Ms. Collins’ house will have to be removed. Since wallboard is a porous material, mold could continue to grow even after the surface is cleaned. It is best to remove drywall at least 12 inches above the obvious water line left by floodwater, since moisture can be absorbed or travel up inside the material. Drywall could be wet on the inside without exhibiting black spots on the exposed wall.

In flood-damaged homes where the water damage is less than four feet high in the room, the lower four feet of the wallboard should be removed. Then the opening can be filled with new 4-ft. x 8-ft. wallboard sheets installed sideways. To lessen the impact of future flooding, mitigation specialists suggest when installing the new wallboard to leave the wall open one inch above the floor joist. The floor baseboard will hide the one-inch gap between the floor structure and the wallboard, but when the baseboard is removed if the house is flooded, the opening will help water drain freely and allow more air circulation to help the materials dry faster.

For more information on mold and cleanup, see the printable brochure “How to Prevent Mold After a Flood” at and the “Molds and Moisture’ section of the Environmental Protection Agency’s Indoor Air Quality site at

Last Updated: 
January 3, 2018 - 12:48