Molds in Your Home
AE-1179, September 1999
Kenneth Hellevang, P.E., Engineer
Health Effects
Exposure to mold is common both inside and outside the home, but some people are more
sensitive to mold than others, especially those with allergies and asthma. Mold exposure
may cause cold-like symptoms, watery eyes, sore throat, wheezing and dizziness, and
trigger asthma attacks.
Because some mold spores are very small and can easily be breathed deeply into the
lungs, it is not safe to live in houses with high mold levels. Exposure to high spore
levels can cause the development of an allergy to mold.
Detection of Mold
Molds can usually be detected by a musty odor, and discoloration of surfaces is common
with mold growth. The mold may change surfaces to white, green, brown, black or orange.
If you see or smell mold, you have a problem. Reliable sampling for mold can be
expensive since it requires special equipment and training. Testing is not generally
recommended as a first step.
Conditions for Mold Growth
Molds grow on organic materials such as paper, leather, dirt and soap scum. They grow
best at warm temperatures, between 77 and 86 degrees Fahrenheit, although they can grow in
temperatures between 32 and 95 degrees.
Molds grow in moisture. Water leaks, flooding, high relative humidity and condensation
are all situations that increase the growth of mold.
Places Molds Grow
Basements may have mold if they are wet or damp. Moisture seeping through concrete
walls and floors will cause this dampness, resulting in mold on walls, floors, carpeting
and materials (including firewood) that are stored in your basement.
Bathrooms are more likely to have mold growth if exhaust fans are not used while
showering or bathing. Soap scum, shower walls, ceramic tile and fiberglass are all
possible surfaces for mold growth.
Laundry rooms are common places to find mold if damp towels and clothing are present.
Unvented clothes drying, which produces high levels of relative humidity, can also cause
mold growth.
Kitchens are possible sites for mold growth if large amounts of water are boiled using
no exhaust fan. Refrigerator pans in automatic defrosting refrigerators also commonly have
mold.
Closets often have mold growth, especially if clothing is stored damp or dirty or there
is a cool outside wall in the closet. And there's a chance mold will be growing behind
furniture.
How to Prevent Mold
- Cleaning, disinfecting and drying surfaces prevents mold growth. Mold will grow on damp
surfaces within a couple days at normal temperatures.
- Reduce moisture levels in the bathroom by running an exhaust fan during and after
showers.
- Fix plumbing leaks and seepage to prevent the buildup of moisture and prevent the growth
of molds.
- Store clothing dry and clean to prevent the growth of mold on clothes.
- Reduce humidity levels by discontinuing use of a humidifier if the relative humidity is
more than 40 percent, and use dehumidifiers and air conditioners when levels of humidity
are high. Also, ventilate with outside air during the winter when outside temperatures are
colder than indoor temperatures. Ventilating with warm summer air typically increases the
air's relative humidity in a basement.
- Increase the flow of air within your home. Moving furniture away from walls and opening
closet doors to permit air circulation limits the growth of molds.
- Prevent condensation. Insulating walls and installing storm or thermal pane windows
keeps walls warm and limits condensation.
Cleanup and Removal of Mold
- Materials should be dried quickly; mold will grow within about 2 days.
- Anyone spending more than a brief time cleaning in a moldy environment should use a HEPA
filter mask; typically it will have two straps. Also, use gloves.
- Porous materials should be thrown out or completely decontaminated if they are moldy.
Materials such as hard plastic, glass and metal can be cleaned and disinfected.
- Remove the mold using a non-ammonia soap or detergent. Never mix bleach and ammonia.
Surfaces from which the mold cannot be completely removed should be treated with enough
chlorine bleach to keep the surface moist for at least 15 minutes, rinsed, then rapidly
dried.
- Disinfect by applying a solution of 1 cup chlorine bleach per 1 gallon water or follow
manufacturer's recommendations. The surface should be thoroughly wetted with the solution.
Keep the surface wet with the bleach solution 10 to 15 minutes to kill the mold. Allow the
solution to dry naturally 6 to 8 hours.
Other products that kill mold are biocides. These biocides have Environmental Protection
Agency (EPA) registration numbers on the bottle and instructions for the intended
application.
Methods to Remove Mold from Various Products
Painted Surfaces Inside the Home
Scrub moldy surfaces with a solution of 1 cup chlorine bleach to 1 gallon water. A little
detergent may be added to the solution, but do not mix bleach with cleaners containing
ammonia. Rinse with clean water and allow to dry thoroughly before painting or papering.
Painted Exterior Surfaces
Scrub mold on paint with a solution of 1/3 cup detergent that does not contain ammonia, 1
quart chlorine bleach and 3 quarts water.
Bathrooms
Scrub surfaces with a solution of 1 cup chlorine bleach, 1 tablespoon detergent that does
not contain ammonia and 1 gallon water. Keep the surface wet for about 10 minutes, then
rinse well with water and dry.
Roofs with Asphalt Shingles and Fiberglass Panels
Use a mixture of 3 parts chlorine bleach and 1 part water at the rate of 1 gallon per
about 40 square feet. This solution will damage metal rain gutters and plants, so control
runoff and rinse surfaces contacted by the solution.
Wood Shingles, Decks and Other Untreated Wood
Scrub surfaces with a solution of 1 quart chlorine bleach and 1 ounce detergent in 3
quarts water. Rinse thoroughly. If stains remain, increase the concentration of bleach to
water and re-treat. Allow wood to dry thoroughly before painting or enclosing.
Clothing and Other Textiles
Brush, shake, sun and air mildewed textiles outdoors. Launder washable items with
detergent and chlorine bleach when appropriate.
Leathers
Dyes used on leathers are very sensitive to numerous substances. Moisten a cloth with a
solution of 1 cup denatured alcohol to 1 cup water, wipe away visible mold, dry in
circulating air.
Carpet and Rugs
Discard pads containing mold. It is nearly impossible to clean and destroy all the mold in
a pad. It is best to hire a professional carpet cleaner or restorer to clean wall-to-wall
carpet. If you try to save the carpet yourself, apply rug shampoo with a carpet shampooer
according to manufacturer's directions. Expose mold growing on the back of carpet to the
direct rays of the sun. Paint the carpet backing with a solution of 1/4 teaspoon chlorine
bleach to 1 cup water or another sanitizing product applied according to the label
directions. Rinse several times. After shampooing and sanitizing, dry the carpet or rugs
quickly by laying outdoors in the sun and wind, or use fans to speed drying.
Upholstered Furniture and Mattresses
Brush surface mold away with a broom outdoors. Vacuum using an upholstery attachment.
Discard the disposable vacuum cleaner bag. Use the services of a professional upholstery
cleaner, or sponge the item with detergent suds and wipe with a clean cloth. Avoid getting
the stuffing wet. Wipe the furniture with a cloth moistened with a solution of 1 cup
denatured or rubbing alcohol to 1 cup water and dry thoroughly. Place the item in the sun
for a few hours and air it thoroughly or use a fan and indirect heat to dry. If mold is
growing deep in the padding of an upholstered piece, nothing will eliminate the mold or
odor except renovation or replacement.
Books
Stand books on end. Spread out pages to dry. Wipe off mold with a clean, dry cloth. After
a few hours, stack and press to avoid wrinkling. Alternate opening and stacking until
completely dry. Sprinkle talcum powder or cornstarch on pages to absorb moisture. Books
may be frozen until you have time to work with them. Place books in a closed container
with moth crystals to stop mold growth.
AE-1179, September 1999
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