Mould, Moisture, and Your Home

Mould Basics

The key to mould control is moisture control. If mould is a problem in your home, you should clean up the mould promptly and fix the water problem. It is important to dry water-damaged areas and items within 24-36 hours to prevent mould growth.

Why is mould growing in my home?

Moulds are part of the natural environment. Outdoors, moulds play a part in nature by breaking down dead organic matter such as fallen leaves and dead trees, but indoors, mould growth should be avoided. Moulds reproduce by means of tiny spores; the spores are invisible to the naked eye and float through outdoor and indoor air. Mould may begin growing indoors when mould spores land on surfaces that are wet. There are many types of mould, and none of them will grow without water or moisture.

Can mould cause health problems?

Moulds are usually not a problem indoors, unless mould spores land on a wet or damp spot and begin growing. Moulds have the potential to cause health problems. Moulds produce allergens (substances that can cause allergic reactions), irritants, and in some cases, potentially toxic substances (mycotoxins). Inhaling or touching mould or mould spores may cause allergic reactions in sensitive individuals. Allergic responses include hay fever-type symptoms, such as sneezing, runny nose, red eyes, and skin rash (dermatitis). Allergic reactions to mould are common. They can be immediate or delayed. Moulds can also cause asthma attacks in people with asthma who are allergic to mould. In addition, mould exposure can irritate the eyes, skin, nose, throat, and lungs of both mould-allergic and non-allergic people. Symptoms other than the allergic and irritant types are not commonly reported as a result of inhaling mould. Research on mould and health effects is ongoing. This brochure provides a brief overview; it does not describe all potential health effects related to mould exposure. For more detailed information consult a health professional. You may also wish to consult your local health department.

How do I get rid of mould?

It is impossible to get rid of all mould and mould spores indoors; some mould spores will be found floating through the air and in house dust. The mould spores will not grow if moisture is not present. Indoor mould growth can and should be prevented or controlled by controlling moisture indoors. If there is mould growth in your home, you must clean up the mould and fix the water problem. If you clean up the mould, but don't fix the water problem, then, most likely, the mould problem will come back.

Tips and Techniques

The tips and techniques presented in this section will help you clean up your mould problem. Professional cleaners or remediators may use methods not covered in this publication. Please note that mould may cause staining and cosmetic damage. It may not be possible to clean an item so that its original appearance is restored.

Fix plumbing leaks and other water problems as soon as possible. Dry all items completely. Scrub mould off hard surfaces with detergent and water, and dry completely. Absorbent or porous materials, such as ceiling tiles and carpet, may have to be thrown away if they become mouldy. Mould can grow on or fill in the empty spaces and crevices of porous materials, so the mold may be difficult or impossible to remove completely. Avoid exposing yourself or others to mould. Do not paint or caulk mouldy surfaces. Clean up the mould and dry the surfaces before painting. Paint applied over mouldy surfaces is likely to peel. If you are unsure about how to clean an item, or if the item is expensive or of sentimental value, you may wish to consult a specialist. Specialists in furniture repair, restoration, painting, art restoration and conservation, carpet and rug cleaning, water damage, and fire or water restoration are commonly listed in phone books. Be sure to ask for and check references. Look for specialists who are affiliated with professional organizations.

Moisture and Mould Prevention and Control Tips

Moisture control is the key to mould control, so when water leaks or spills occur indoors - ACT QUICKLY. If wet or damp materials or areas are dried 24-36 hours after a leak or spill happens, in most cases mould will not grow. Clean and repair roof gutters regularly. Make sure the ground slopes away from the building foundation, so that water does not enter or collect around the foundation. Keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly. Keep indoor humidity low. If possible, keep indoor humidity below 50 percent (ideally between 30 and 45 percent) relative humidity. Relative humidity can be measured with a moisture or humidity meter, a small, inexpensive ($10-$50) instrument available at many hardware stores. If you see condensation or moisture collecting on windows, walls or pipes ACT QUICKLY to dry the wet surface and reduce the moisture/water source. Condensation can be a sign of high humidity.

Actions that will help to reduce humidity:

Vent appliances that produce moisture, such as clothes dryers, stoves, and kerosene heaters to the outside where possible. (Combustion appliances such as stoves and kerosene heaters produce water vapour and will increase the humidity unless vented to the outside.) Use air conditioners and/or de-humidifiers when needed. Run the bathroom fan or open the window when showering. Use exhaust fans or open windows whenever cooking, running the dishwasher or washing dishes, etc.
Actions that will help prevent condensation:

Reduce the humidity (see above).
Increase ventilation or air movement by opening doors and/or windows, when practical. Use fans as needed.
Cover cold surfaces, such as cold water pipes, with insulation.
Increase air temperature.

Cleanup and Biocides

Biocides are substances that can destroy living organisms. The use of a chemical or biocide that kills organisms such as mould (chlorine bleach, for example) is not recommended as a routine practice during mould cleanup. There may be instances, however, when professional judgment may indicate its use (for example, when immune-compromised individuals are present). In most cases, it is not possible or desirable to sterilize an area; a background level of mold spores will remain - these spores will not grow if the moisture problem has been resolved. If you choose to use disinfectants or biocides, always ventilate the area and exhaust the air to the outdoors. Never mix chlorine bleach solution with other cleaning solutions or detergents that contain ammonia because toxic fumes could be produced.

Please note: Dead mould may still cause allergic reactions in some people, so it is not enough to simply kill the mould, it must also be removed.