Preventing Mildew and Decay

Claudette Reichel, Skinner, Patricia  |  3/17/2005 2:07:55 AM

Add together: post-storm dampness; water leakage; warm, humid weather; and no air conditioning because of power outages. What do you get? A mildew population explosion. In fact, even one of these factors can create serious mildew problems, so a combination can lead to a major problem days or weeks after the storm. All in all, the secret to mildew prevention and control is two words -- clean and dry.

Health & Safety Alert:

Molds can pose a health hazard, especially for infants, the elderly and those with asthma, allergies or illnesses. If mold is present, or materials have not been cleaned and dried within two or three days of the floodwater receding, then vulnerable people should stay away during restoration, and precautions should be taken to protect workers. Protective rubber gloves, goggles and well-fitting respirators with toxic particle (purple) cartridges are recommended; dust masks are not adequate.


Remove Wet Insulation & Clean Moldy Wood

Wet insulation holds water against wood sills and studs. Wet wood is subject to decay and breeds mold that can cause musty odors and health hazards weeks or months after the flooding or leaks occurred.

  • Find, remove and discard all wet fiberglass, mineral wool, cellulose or open-cell spray foam insulation.
  • Use non-phosphate cleaner to clean silt and mold from wet wood.  You may also choose to spray the wall cavity with a disinfecting solution to kill bacteria and any mold remaining after cleaning.  
  • Allow the wood to dry completely before replacing insulation and completing repairs. That can take weeks in humid weather.
  • Saturated carpeting and pads may not dry out before mildew takes hold. The telltale odor will begin in a few days, followed by growing dark stains that may not be removable.
  • Loosen and fold back wet sections of carpet or remove the carpet for disposal or cleaning outdoors, if valuable enough to attempt salvage.
  • Cut out wet padding and discard.
  • Disinfect the subfloor and wet carpet backing by lightly spraying with disinfecting solution. Do not spray the carpeting (top side) with chlorine bleach solution. Do not use disinfecting solution on wool carpet.
  • If mildew appears on the carpet, sponge lightly with a solution of one part of 3% hydrogen peroxide to five parts water (add sunshine if possible). Test first for colorfastness.
  • Do not reinstall or reattach the carpeting until carpet and floor are thoroughly dry. The carpet may shrink, but it can usually be stretched back into place by a professional installer.

Reduce Humidity

Although wet insulation and carpeting pose the biggest mildew hazards, any home surface is subject to mildew when it is damp or the air is humid.

  • Fully air condition all rooms for a few days with open closets; air conditioners remove moisture from the air.
  • Use exhaust fans during and 30 minutes after cooking and bathing.
  • If possible, use dehumidifiers to speed the drying process.
  • If you have no power for air conditioning, keep curtains, rooms and closets open to get maximum air circulation and sunshine.

Act Quickly to Remove Mildew  

Dirt and grease are food for mildew, so clean surfaces are more mildew resistant. When mildew appears, act promptly. Once mildew takes over, it is much more difficult to control. Mildewed items that can be moved should be taken outside for cleaning to avoid adding mold spores to the indoor air. Sunning damp items will also help to kill mildew and dry them.

Water-tolerant Interior Surfaces 

Sponge or spray colorfast interior home surfaces with a solution of 1/2 - 3/4 cup chlorine bleach to one gallon of water. This will not generally harm most bathroom and painted surfaces, but it is best to test it on an inconspicuous area first. Rinse painted surfaces with clean water and dry thoroughly.

If interior walls need cleaning as well as mildew control, mix up to 1/2 cup of a nonphosphate powdered household cleaner in the bleach-water solution. Never mix ammonia, acids or products containing ammonia with chlorine bleach.

Wood Floors and Furniture 

Don’t use water to clean wood furniture and floors unless you plan to refinish them. First try to remove mildew with commercial wood cleaners. If that doesn’t work, wipe with a soft cloth dipped in a mild all-purpose detergent and water solution and wrung almost dry. Quickly rinse with a clean, damp cloth. Dry each area thoroughly before proceeding to the next spot.

If mildew has grown into the finish or the wood, scrub the stains with the bleach and water solution and refinish. Deep stains may need stronger bleach-cleanser-water solutions or sanding.

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