If you live in a damp house, or if you have ever experienced flooding, your home may be breeding an often-invisible and always unwelcome intruder - mold.

Mold can cause allergies and respiratory disease. The toxins it produces can wear down the immune system — leaving people, especially children, vulnerable to many illnesses. If you discover mold, it’s important to destroy it quickly. It’s equally as important that you take precautions before you begin. Whether you do the job yourself or hire a contractor, the following steps should be taken to destroy molds and prevent them from reinfecting your home.

Mold identification

• Molds are micro-organisms that feed on a variety of indoor substances found especially, but not exclusively, in dust and dirt. They can grow on or in anything, including dirty glass, drywall, wood, plastic or fabrics.
• Molds grow only in damp conditions, and are most commonly found in basements, kitchens or bathrooms. Even if the air in your house is generally dry, they can flourish in the damp local climates that occur in many Canadian homes.
• Molds are not always easy to recognize. They often look like a simple stain, smudge or discoloration. Sometimes they give off a musty or earthy odour or smell faintly like alcohol.
• To identify a mold, dab suspected marks with a drop of chlorine bleach. (Note the precautions to take when working with chlorine bleach.) If the colour changes or disappears, the stain is likely organic and probably a mold.

Special precautions

• When working on mold patches, always protect yourself with an appropriate face mask. For small localized areas, use an inexpensive disposable face mask, which you can buy at a hardware store; for larger areas, use a full-face respirator with an approved, disposable HEPA filter, which you can obtain from a safety supply store.
• Never mix an ammonia detergent with bleach - it releases dangerous chlorine gas.
• Always ventilate your work area when using bleach - open two outside doors or windows, one into the wind and the second facing away. If necessary, use a fan to increase the air flow.
• Vigorous vacuuming may increase your exposure to mold spores, which can pass through ordinary vacuum filters and remain suspended in the air for hours or days. Central vacuums that vent outside, or vacuums fitted with HEPA filters, will help minimize this exposure.

How to treat surface mold

• Chlorine bleach is the only product that kills molds on contact. Remember that bleach is a strong chemical that should be handled carefully.
• Wear protective gloves and an appropriate face mask.
• Ensure excellent ventilation in the area.
• Bathe the stain in chlorine bleach, full strength.
• Keep the affected area soaked in bleach for 15 minutes.
• After you have killed off mold patches, carefully wash down the entire area with the recommended bleach cleanser, rinse thoroughly, and dry quickly.

Recommended Bleach Cleanser

Mix one part chlorine bleach, four parts water, and a few drops of non-ammonia dishwashing detergent to cut surface grease and grime.

How to treat whole-house mold

• If you find one patch of mold, conduct a thorough search of your house for others. Kill all the patches with chlorine bleach and then, using the recommended bleach cleanser, conduct an old-fashioned, top-to-bottom “spring cleaning” — whatever the season.
• Cleaning a very mold-troubled house will involve exposure to clouds of spores, so be sure to wear gloves, protective clothing and a face mask with a HEPA filter.
• Anything that has been wet for days or damp for weeks must be thrown out. This may seem drastic but it is often the least expensive and quickest way to get rid of dangerous molds.
• It’s important to discard any moldy items with which you come into close daily contact, especially mattresses, pillows, bedding, upholstery or children’s plush toys. Each time you use or clean a moldy mattress or upholstered furniture it re-injects mold material into the air.
• Bleachable clothing should be washed with a solution of detergent and one cup bleach per washer load and then rinsed well. Repeat if necessary. Slightly musty clothing that cannot be bleached may sometimes be cleaned with baking soda, washing soda or borax. Dry cleaning is an alternative for non-bleachable fabrics.
• Moldy carpets, which can trap more mold than any other material, should be scrapped unless they are rare or expensive. They can be dry-cleaned but the cost is high. If carpets smell only slightly musty, vacuum them, brush in a large amount of baking soda and leave for three or four days, then vacuum thoroughly again. Alternatively, you can steam clean them lightly and dry them rapidly. Do not soak!
• Very moldy furniture should be discarded. If it is valuable, decontaminate the stripped frame and reupholster. If mold damage is not obvious, vacuum, dust with baking soda and scrub it in, leave for three or four days, then re-vacuum. Finally, air it out in the sun.
• Washable drapes that can be safely bleached may be salvageable. Dry-cleaning should be done by a professional who knows how to remove molds.
• All non-moldy surfaces — walls, ceilings and floors — can be scrubbed with the recommended bleach cleanser, rinsed and dried thoroughly and quickly.
• All non-electrical equipment, such as duct work, can be vacuumed, wet-wiped, rinsed and dried.
• Light fixtures, wiring boxes and appliances should be vacuumed with a plastic wand after turning off breakers or removing fuses. Check to make sure the circuit is not live!
• Moldy books and papers are difficult to treat. If they are valuable, dust between each page with baking soda, put the materials in a plastic bag and place them in the sun for several hours. When the items are odour-free, vacuum or wipe them, using gloves to protect your skin.

An ounce of prevention

• The best way to prevent mold growth is to keep all materials in your home as clean and dry as possible. Keep your home well ventilated and the relative humidity between 30 and 50 per cent. (See CMHC publication Measuring Humidity in your Home — CE1.)
• Find and correct obvious sources of moisture, such as leaky faucets, dripping pipes and cold surfaces where moisture condenses.
• Regularly clean off, then dry, all surfaces where moisture frequently collects in your house. Clean with a baking soda solution one day, and vinegar the next to keep molds at bay. (Baking soda and vinegar each kill different types of mold.)