Mould is a fungus that grows on, or in, damp and decaying vegetable matter. Moulds are microorganisms that cause allergies, asthma, and other health problems. Mould is not a friendly cohabiter, and experts say: People should not live in mouldy houses!

When mould is found in housing units, it should be removed for the long-term health and comfort of the occupants. As moulds are not desirable indoors, and are relatively easy to get rid of, it is advisable to act before health problems arise.


One of the problems with mould is identifying it. A reasonably reliable test is to dab the stain/mark with a chlorine bleach solution and observe any changes in colour. If the colour is entirely or largely removed, the stain is likely organic and probably mould. If not, the stain/mark is probably non-organic and need not be treated as a dangerous mould.


It is not always easy to determine whether mould is a problem in a house. Many tell-tale signs, including smell, indicate that a house is obviously affected, although the absence of smell does not guarantee that mould is not a problem.

Good Houses: In good houses, there are no mould smells, and all indoor spaces, surfaces and materials are free from water stains and mould. Houses should be checked regularly to see that they continue to meet these minimum standards.

Bad Houses: If a house smells mouldy, musty, or earthy, action should be taken. Obvious signs are water damage indoors, mould (or mould stains), and rot. A house with any of these warning symptoms should be considered a bad house, especially if some occupants have vague, but persistent symptoms of fatigue or allergies.


To avoid mould problems indoors, we must keep surfaces dry, and the relative humidity of the air reasonably low (below 70% all year, and below 55% in the winter). The best preventive methods are to keep all surfaces as clean and dry as possible, and to prevent indoor air from becoming too moist.

Once a problem occurs, more aggressive measures are required. Indoor mould spores must be removed and killed; and any toxic material they produce should be removed. First, items that are mouldy must be identified. The most common sites for mould to occur in the household will each be discussed next.

Beds and Bedding

General: Since beds and bedding are close to us for many hours every day, higher standards should be applied to them than to other household items. Beds are very effective redispersal devices: they send settled particles back into the air, and spew out mould spores and mycelia as we move about during the night. Plastic covers are very little help unless the covers remain airtight. If bags do not remain tight, mould can continue to grow on bedding material inside the bag, and then vent out through leaks.

Mouldy: If mattresses are mouldy, or badly water stained, they should be discarded. It is impossible to clean a mouldy mattress because so much of the material is inaccessible. Mattresses, pillows and bedding that have been stored in wet basements should also be discarded. The health costs of using them will far outweigh the costs of replacing them.

Uncertain: If a lightly water-damaged mattress does not smell of mould, but does not smell fresh, it should be sprinkled generously with baking soda. The mattress should then be brushed vigorously, vacuumed carefully after several hours, then placed in the sun and rotated several times so that all surfaces are exposed to the sunlight for hours at a time.


General: Clothing must be clean and uncontaminated because it comes into contact with our skin, and because it is often close to our noses. Fortunately, clothing is portable and need not be cleaned at home.

Mouldy: Very mouldy or mildewed clothing should be bleached, if possible, and well washed and rinsed. Repeat the wash and rinse cycle if clothing does not pass the sniff test. If the clothing cannot be bleached, try washing with baking soda or borax. The clothing should be rapidly and thoroughly dried, then stored in a dry decontaminated area. All items should be well aired in sunlight after cleaning, as ultraviolet rays are an effective fungicidal treatment.

Uncertain: Clothing that smells mildly musty and does not look water stained should be washed well and then tested for residual smell. Airing in the sun is a good finishing touch.


General: Carpets are among the indoor materials most likely to be affected by moisture and mould. They also greatly affect indoor air quality as they have a large surface area; they store large amounts of dirt and mould spores; and they can become quite damp if they are on a cold floor or can absorb condensation from a window or humidifier. While mould can often be seen on windows, it is hidden in carpets.

Mouldy: Carpets that get wet and mouldy because they are not completely dried in a short time should be scrapped. Expensive area carpets may merit the costs of dry cleaning, but ordinary carpets will not.

Uncertain: When carpets smell slightly mouldy because there is a severe mould problem in the house, dry steam the carpet and rapidly dry it. This can only be done when the room is well ventilated and the outdoor air is very dry. The carpet must be completely dry within hours. Beware of anti-fungal treatments; they may be more dangerous to the occupants than the mould that is being removed!


General: Drapes, particularly the insulating variety, can become heavily contaminated with mould. Condensation becomes a factor if it is cold outside, or if the drapes touch cold outside walls. Because drapes have a very large surface area, they can hold a lot of mould material, then release it when they dry out.

Mouldy: If drapes are washable and can be safely bleached, the best treatment is to bleach and wash them in a good detergent. Alternatively, they can be dry-cleaned. Air the drapes in the sun before bringing them back indoors. The sources of mould and excessive condensation should be treated before the drapes are re-hung.

Uncertain: If drapes have been exposed to indoor air that is contaminated with moulds, they should be cleaned and aired to remove all traces of spores and mycelia that may cling to the fibres. Air them well before re-hanging.

Upholstered Furnishings

General: Like bedding, upholstered furniture can re-inject dust and mould material into the air when it is used or cleaned. Therefore, it must be treated very carefully and thoroughly.

Mouldy: Very mouldy furniture should be discarded. If it is valuable, the frame should be decontaminated and then re- upholstered. If the mould smell is strong, but mould or water damage is not obvious, furniture can sometimes be saved with a thorough vacuuming, a dusting, and brushing with baking soda. The piece should be aired in the sun, with all sides exposed to sunlight, and vacuumed again.

Uncertain: If the upholstery is exposed to mouldy air, it can pick up enough mould material to take on a bad smell, even if mould never directly grows on it. A thorough vacuuming and deodorization with baking soda can remove odours in all but the worst cases. The piece should be thoroughly aired in the sun.

Walls, Ceilings and Uncarpeted Floors

General: Walls, ceilings and uncarpeted floors make up a large total surface area, but normally hold less significant amounts of mould materials then smaller but more porous surfaces. However, they are important because the large surface is in contact with the indoor air we breathe.

Mouldy: Clean badly moulded surfaces with pure chlorine bleach, and rewet so that the surface stays moist for a minimum of 15 minutes. Wash with the bleach-water detergent solution until the surface is obviously clean. Dry rapidly, using plenty of ventilation to prevent new mould growth.

Uncertain: Clean all surfaces in problem houses thoroughly with the solution of bleach, water and detergent. Dry as rapidly as possible.