Believe it or not, everyone has a bit of mould in their home. Just leave some bread in a drawer for a month if you do not believe me. Mould can be helpful – as with penicillin, a small nuisance or a big one for anyone that has dealt with toxic mould.

What is mould?

Moulds 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. There are over 270 species of mould have been identified as living in Canadian homes.

When is it a problem?


Mould needs moisture and certain nutrients to grow. High moisture levels can be the result of water making its way inside from outside the home, 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. Mould can be any colour including more commonly black, white, red, orange, yellow, blue or violet.

Damage to materials is one concern of having mould – i.e.  stains or discolouration; however, continued mould growth can be indicative of moisture conditions favourable for growth of fungi that cause wood rot and structural damage. If mould like this is growing inside the home, there may be health concerns. Moulds release chemicals and spores and health experts indicate that, depending on the type of mould present in a home, the amount and degree of exposure, and the health condition of the occupant, the health effects of mould 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 mould. If you believe that you or someone you know may be at risk, consult your family physician.

How can I tell if I have a mould problem?

Two simple ways to determine if there is mould in your home is discolouration or odour. If you see discolouration on a carpet that you think is due to mould, dab a drop of household bleach onto a suspected spot. If the stain loses its colour or disappears, it may be mould. If there is no change, it probably is not mould. For hidden moulds or those that cannot be seen, a musty or earthy smell often indicates the presence of moulds. But a smell may not be present for all moulds. Even when you do not notice a smell, wet spots, dampness or evidence of a water leak are indications of moisture problems and mould may follow.

Dealing with small mould problems

If you do appear to have mould, if it covers less than a square meter, it is considered “small” (even up to three small patches is not a significant concern). You can clean it up yourself by following the directions below. Make sure to use household rubber gloves and a dust mask for protection. Where vacuuming is recommended, use a vacuum cleaner that has a High Efficiency Particulate Air (HEPA) filter or one that is externally exhausted.

  1. General surfaces (other than those specified below): Start by vacuuming the surfaces. Scrub or brush the mouldy area with a mild unscented detergent solution (do not use bleach), and then sponging it with a clean, wet rag to assist in drying it quickly. Follow again by vacuuming the surfaces that were cleaned as well as surrounding areas.
  2. Wood surfaces: Also start by vacuuming loose mould from wood surfaces. Try cleaning the surface of the wood with unscented 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 mould spores from being dispersed into the air. Note that wood affected by rot may need to be replaced.
  3. Concrete surfaces: Vacuum the concrete surfaces to be cleaned. Clean surfaces with unscented detergent and water. If the surfaces are still visibly mouldy, use one cup of TSP (trisodium phosphate – a.k.a. baking soda) dissolved in two gallons of warm water. Stir for two minutes. Note: TSP must not come in contact with skin or eyes. Saturate the mouldy 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, and then dry thoroughly, as quickly as possible.
  4. Drywall: Drywall will grow mould when it gets wet or repeatedly wet and does not have the chance to dry quickly. Cleaning with water containing detergent not only adds moisture to the paper, but it can eventually damage the facing. If the mould is located only on top of the painted surface, remove it by general cleaning as described above. If the mould is underneath the paint, the mouldy patch and other mouldy material behind it are best cut out and the surrounding areas also cleaned. This should be done by an experienced mould clean-up contractor, because if not done properly the problem can become much larger.

Note that a small clean up should take minutes (not hours) to finish. When the clean up takes hours to a day to finish, you should use more serious precautions (such as upgrade to a better filter, such as a half-face respirator with charcoal cartridges to prevent contamination of other areas of the house as well as provide ventilation).

It is important to note that cleaning these small mouldy areas as you begin to see them is critical, as they become a problem when they are ignored and will grow. Also, if you have tried cleaning up a small area of mould but the mould comes back after cleaning, seek professional help.

Dealing with bigger mould problems

For any larger mould areas, assessment by a professional is recommended. Once you have had a professional assessment, there are instances where you can clean up the mould yourself (e.g. in the case of moderate amounts of mould), but you must use the proper protective equipment and follow the proper procedures (which the professional can provide you with or look for the guide put out by the Canadian Mortgage and Housing Corporation (CMHC).

If moisture is entering the home from the outside, repair to the building envelope will be required. At the same time, steps will need to be taken inside the home to reduce the occupants’ exposure to mould. A professional can provide you with a detailed checklist, but at a high level it will include discarding mouldy or damaged materials and furnishings (as they often become contaminated), isolating the mouldy area with plastic sheeting, washing all clothing in hot water (non washables should be dry cleaned, clothing includes all bedding, pillows, etc.), decluttering excess stored materials, and using a dehumidifier or other machines that keep the area moisture free as well as a hygrometer to measure the moisture levels.

Should you have your home’s air tested for mould?

One of the most often asked questions by homeowners who think their home may have a mould problem is whether they should have the air in their home tested for mould. Testing is generally not recommended for homeowners. Determining whether you have mould and the extent of it is the important part. You have to clean up the mould and correct the problem irrespective of the type of mould. The cost of testing may be better spent hiring a professional investigator or fixing the problem.

Hopefully, if you follow some of these practical tips, you can avoid a small nuisance becoming a big problem.

Understanding mould in the home

By: Yvonne von Jena, The Home Inspection Network

Leave a Reply

Your email address will not be published. Required fields are marked *

clear formPost comment