Fighting Mold — The Homeowners’ Guide
Molds are microscopic fungi, a group of organisms which also includes mushrooms and yeasts. Fungi are highly adapted to grow and reproduce rapidly, producing spores and mycelia in the process.
You encounter mold every day. Foods spoil because of mold. Leaves decay and pieces of wood lying on the ground rot due to mold. That fuzzy black growth on wet window sills is mold. Paper or fabrics stored in a damp place get a musty smell that is due to the action of molds.
Molds can be useful to people. The drug penicillin is obtained from a specific type of mold. Some foods and beverages are made by the actions of molds. The good kinds of molds are selected and grown in a controlled fashion.
Molds are undesirable when they grow where we don’t want them, such as in homes. Over 270 species of mold have been identified as living in Canadian homes. Molds that grow inside may be different from the ones found outdoors.
What makes molds grow?
Molds will grow if we provide them with moisture and nutrients. If we keep things dry, molds do not grow.
High moisture levels can be the result of water coming in from the outside, through the floor, walls or roof; or from plumbing leaks; or moisture produced by the people living in the home, through daily activities like bathing, washing clothes or cooking. Water enters the building when there is a weakness or failure in the structure. Moisture accumulates within the home when there is not enough ventilation to expel that moisture.
Different kinds of molds grow on different materials. Certain kinds of molds like an extremely wet environment. Other kinds of molds may be growing even if no water can be seen. Dampness inside the material can be enough to allow them to grow.
Why are molds a concern?
Damage to materials is one concern. Materials get stained or discoloured, and over time they are ruined. Moldy paper and cardboard disintegrate over time. Fabrics are damaged. Continued mold growth can be indicative of moisture conditions favourable for growth of fungi that cause wood rot and structural damage.
When molds are growing inside the home, there may be health concerns. Molds release chemicals and spores.
Health experts indicate that, depending on the type of mold present in a home, the amount and degree of exposure, and the health condition of the occupant, the health effects of mold can range from being insignificant to causing allergic reactions and illness.
Pregnant women, infants, the elderly and those with health problems, such as respiratory disease or a weakened immune system, are more at risk when exposed to mold. Consult your family physician if you believe there is someone who may be at risk.
Is there a mold problem?
Molds are always found in the air outside and in all buildings. They come into the home in many ways — through open windows or doors, on clothing, pets, food or furniture. The problem starts when mold grows inside the home.
Some mold growing, for example on the window sill but not elsewhere, is not a cause of concern. You can clean the mold yourself. The presence of mold is a sign that there is too much moisture in your home — a situation which must be corrected.
Inspect the home to find the extent of the mold.
How can you tell if it is mold?
Discoloration is a sign of mold. However, all discoloration is not due to mold. Carpeting near baseboards, for example, can be stained by outdoor pollution entering the home. Stains or soot may also be caused by the smoke from burning candles or cigarettes.
Mold may be any colour: black, white, red, orange, yellow, blue or violet. Dab a drop of household bleach onto a suspected spot. If the stain loses its colour or disappears, it may be mold. If there is no change, it probably isn’t mold.
Sometimes molds are hidden and cannot be seen. A musty or earthy smell often indicates the presence of molds. But a smell may not be present for all molds. Even when you don’t notice a smell, wet spots, dampness or evidence of a water leak are indications of moisture problems and mold may follow.
How much mold is growing?
One way to know is to estimate the area of the mold.
Mold is considered to cover a “small area” if the patch is no larger than a square meter. There should be no more than three patches, each patch smaller than a square meter. Clean up small areas yourself using a detergent solution, household rubber gloves and a dust mask for protection. Refer to How to clean-up small problems for the procedure.
Small moldy areas in homes may become larger over time, if ignored, so it’s important to clean up and remove even small patches of mold.
The mold area is considered “moderate” if there are more than three patches, each patch smaller than a square meter, or there is one or more isolated patches larger than a square meter but smaller than 3 square metres (size of a 4 x 8 foot sheet of plywood). Assessment by a professional is recommended. You can clean up moderate amounts of mold but you must follow the proper procedures and use the proper protective equipment. Refer to Moderate area clean-up for the procedure.
A mold area is considered “extensive” if a single patch of mold is larger in area than a sheet of plywood. Being exposed to this much mold is not a good idea. Do not attempt to clean up large areas of mold yourself. You need professional help to determine why the mold is there in the first place and how to clean it up.
When should you seek professional help?
You may need professional help when:
How do you get professional help?
Contact your local CMHC office for a list of individuals who have completed the CMHC Residential Indoor Air Quality Investigator program. A trained IAQ investigator, who operates a private business and sells his/her services, examines the indoor air quality of your home and documents your concerns. He/she identifies the problems, finds their sources and suggests solutions in a written report. Recommendations are provided to you in an action plan that consists of various options to improve the indoor air quality in your home.
Bleach is NOT recommended
The presence of organic (humic) materials, the pH (acidity/alkalinity) of the water, the surface material and contact time affect the effectiveness of bleach for disinfection. Since these factors are not generally controlled, bleach cannot be relied upon for disinfection. The most compelling reason for advising against bleach is that fumes are harmful but in addition, overuse of bleach will result in increased releases of chlorinated effluents which can be harmful to the environment.
“Small area” clean-up
You can clean up “small areas” of mold (fewer than three patches, each smaller than a square meter) yourself. The minimum protective wear needed are:
Infants and other family members with asthma, allergies or other health problems should not be in the work area or adjacent room during the cleaning.
Scrub with an unscented detergent solution; then sponge with a clean, wet rag and dry quickly.
Using an unscented detergent will make it easier for you to detect residual moldy odours.
Clean the surface with a damp rag using baking soda or a bit of detergent. Do not allow the drywall to get too wet.
Mold that comes back after cleaning is usually an indication that a source of moisture has not been removed. Seek professional help from a trained IAQ investigator.
If you follow the proper procedures and use the proper protective equipment, you can clean up “moderate areas” of mold. “Moderate” means more than 3 patches of mold, each smaller than one square meter, or one or more isolated patches larger than one square meter but smaller than 3 square meters (size of a 4 x 8 foot sheet of plywood).
A small clean up should take minutes (not hours) to finish. When the clean up takes hours to a day to finish, it is suggested that you upgrade to a better filter, such as a half-face respirator with charcoal cartridges. An exhaust fan installed in a window in the room being cleaned would prevent contamination of other areas of the house as well as provide ventilation.
Vacuum surfaces with a vacuum cleaner which has a High Efficiency Particulate Air (HEPA) filter or is externally exhausted. Scrub or brush the moldy area with a mild unscented detergent solution. Rinse by sponging with a clean, wet rag. Repeat. Dry quickly. HEPA vacuum the surfaces that were cleaned as well as surrounding areas.
Cleaning wood surfaces
Vacuum loose mold from wood surfaces using a HEPA or externally exhausted vacuum. Try cleaning the surface of the wood with detergent and water. Rinse with a clean, damp rag and dry quickly. If the staining does not come off, sand and vacuum the surface of the wood with a vacuum/sander combination. It is important to vacuum at the same time to prevent mold spores from being dispersed into the air. Note that wood affected by rot may need to be replaced.
Cleaning concrete surfaces
Vacuum the concrete surfaces to be cleaned with a HEPA or externally exhausted vacuum cleaner. Clean up surfaces with detergent and water. If the surfaces are still visibly moldy, use TSP (trisodium phosphate). Dissolve one cup of TSP in two gallons of warm water. Stir for two minutes. Note: TSP must not be allowed to come in contact with skin or eyes. Saturate the moldy concrete surface with the TSP solution using a sponge or rag. Keep the surface wetted for at least 15 minutes. Rinse the concrete surface twice with clean water. Dry thoroughly, as quickly as possible.
The paper facings of gypsum wallboard (drywall) grow mold when they get wet or repeatedly wet and don’t dry quickly. Cleaning with water containing detergent not only add moisture to the paper but also can eventually damage the facing. If the mold is located only on top of the painted surface, remove it by general cleaning (see above). If the mold is underneath the paint, the moldy patch and other moldy material behind it are best cut out and the surrounding areas also cleaned. This should be done by a mold clean-up contractor. New materials may become moldy if the moisture entry has not been stopped. If this is the case, replacement of the materials should be deferred until the source of the moisture is corrected. The affected areas should be temporarily covered with plastic sheeting and sealed at the edges.
Any areas that show new patches of mold should be cleaned promptly.
Dealing with an ongoing problem
Repair to the building envelope is required if moisture is entering the home from the outside. At the same time, steps should be taken inside the home to reduce the occupants’ exposure to mold.
Step 1 — Discard moldy or damaged materials
Wear a dust mask and gloves. Furnishings, such as mattresses, carpets, or sofas that got wet or have been stored in damp conditions should be discarded. Discard items that are no longer needed. Use this opportunity to reduce the amount of furnishings — this means fewer materials to absorb moisture and grow mold. Clothes and other items that have been cleaned should be stored in sealed plastic bags to prevent re-contamination.
Step 2 — Vacuum
Proper vacuuming reduces the amount of mold spores. All surfaces in the home (floors, walls, ceilings, shelves) and non-washable furnishings (such as sofas, chairs, etc.) must be vacuumed thoroughly.
Step 3 — Prevent
Keep moisture generated within the home to a minimum by conscientiously following the prevention steps presented in the next section.
Step 4 — Clear wet areas
Pull carpets and furnishings away from walls that get wet. Carpets and underpads that are moldy should be cut out and discarded.
Step 5 — Dry
Take steps to dry up areas that get wet. Monitor the relative humidity of the air. Use a portable dehumidifier, if necessary. Ensure that the condensate drain pan of the dehumidifier is emptied regularly.
Step 6 — Isolate
If the mold is limited to one area, isolate the area if possible. Cover the affected surfaces with plastic sheeting secured at the edges with duct tape. Note that this is only a temporary measure to minimize your exposure.
Step 7 — Clean
Healthy individuals can regularly clean “small” and “moderate” areas of mold, thus preventing these from getting out of hand, by following the safety precautions and cleaning guidelines.
Step 8 — Seek professional help
Consider seeking professional help from trained IAQ investigators to identify appropriate remediation steps inside the home. Removing large amounts of mold will require the services of mold clean-up contractors.
Basic steps to prevent and reduce mold growth
Mold needs moisture to grow. Controlling the moisture and keeping the home dry prevents the growth of mold.
Mold-proofing your home, room by room
Basement or crawl space
To clean a drain:
If the drain is still clogged, use a small plumbing snake.
Closets and bedrooms
Other parts of the home
Frequently asked questions about mold
Should I have my house air tested for mold?
This is the question most frequently asked by homeowners who think their home may have a mold problem. Testing is generally not recommended for homeowners. Testing of moldy materials or an air sample identifies the types of molds that may be present but does not identify the cause/source of moisture. The type of mold does not change the procedures for cleaning up areas of mold less than 3 square meters. You have to clean up the mold and correct the problem irrespective of the type of mold. The cost of testing may be better spent hiring a professional investigator or fixing the problem.
Testing of a moldy material involves sending a swab, an imprint on a Scotch tape or a piece of the material to a competent laboratory. Air sampling requires specialized equipment. An air sample typically captures mold spores in a period of minutes. Since replicate samples must be taken due to variations in the airborne molds over time (even hours) and compared with outdoor samples, air testing is both expensive and time-consuming. Interpretation of test results may not be very useful, since there are no advocated “safe levels” of indoor molds and the results will not tell the health risks from the molds.
The air feels dry — can I humidify?
Before you add moisture to the air, measure the relative humidity. Air that feels dry may not be really dry. It may be moldy. High relative humidity (over 45 per cent) promotes the growth of molds and dust mites. The moisture in the air may condense on colder exterior walls where molds start to grow.
If your physician has advised you to use a humidifier in your child’s bedroom at night, monitor the relative humidity. Turn the humidifier on and off as necessary. In the morning, take steps to make sure the room gets dry. Clean and empty the humidifier after each use.
Ordinary vacuums capture large particles only — small mold spores pass through the vacuum into the air. HEPA vacuums have special filters that capture small particles. A central vacuum cleaner which is exhausted to the outside also removes mold spores. A regular portable vacuum is useful only if its exhaust goes outside the home. Vacuuming removes settled dust that contains an accumulation of mold spores over time. Reducing the settled dust reduces molds.
Vacuuming with any vacuum cleaner (ordinary, central or HEPA) stirs dust and mold during the process. Wear a dust mask so you will not be breathing more mold.
Is vacuuming with a HEPA or externally exhausted vacuum cleaner recommended for serious mold problems only?
Vacuum regularly with a HEPA or externally exhausted vacuum cleaner to prevent the ongoing accumulation of dust and molds. The need for HEPA or external exhaust vacuuming increases with the severity of the mold problem.
If a furnishing has been wet at some time in the past or has been exposed to dampness over a prolonged period of time, vacuuming with HEPA or externally exhausted vacuum is unlikely to remove the mold growing beneath the surface. It is better to discard the item.
Where do you find a HEPA vacuum cleaner?
Vacuum cleaner dealers carry HEPA vacuums. Consider purchasing one as an upgrade to what you may be using. A HEPA vacuum is a good investment in the long term whether you have mold or not. A generic canister HEPA vacuum cleaner costs approximately $300. Brand name products of the same type may cost more. You may inquire if the dealer has a HEPA vacuum cleaner to rent. Contractors who clean up or renovate houses for mold should also have this equipment.
Does painting over a moldy surface take care of the mold?
Painting over mold only masks the problem. Paint does not kill the mold nor stop it from growing. Surfaces that are washable should be cleaned with a detergent solution, following the procedure suggested above, then allowed to dry. If you are going to paint, remove mold first.
Does cleaning stop the mold growth?
Mold will reappear until its source of moisture is removed. High moisture levels that are not corrected can make the molds grow back quickly. Cleaning is only a temporary but essential measure.
You can help by making a conscious effort to keep the home dry. Obviously, water must be prevented from entering the home. But you can help by controlling moisture that you produce.
How does one clean clothes that are moldy?
Non-washable clothing can be dry cleaned.
Wash clothes with a detergent solution to which a cup of bleach is added. Make sure the detergent you use does not contain ammonia. Repeat as necessary until the moldy odour is gone.
Clothes and other items that have been cleaned should be stored in sealed plastic bags to prevent re-contamination.