Moulds are a type of fungi that require moisture and a food source to grow. They reproduce by releasing vast numbers of tiny spores into the air which can be inhaled.

If inhaled in large quantities, some mould spores can cause health problems such as allergic reactions similar to hay fever, breathing difficulties, eye irritation, skin rashes and occasionally, more serious symptoms.

Mould and leaking buildings

Leaking buildings are likely to have mould in wall cavities as the conditions are well suited for fungal growth.

Mould growth can often be seen as surface discolouration on ceilings, walls and furniture. There may also be a musty smell. If there is any evidence of water damage, there is likely to be mould growth.

There is no effective way of eliminating mould spores – the best way to control indoor mould growth is to control indoor moisture.

Proper precautions must be taken to ensure that workers and building occupants are not exposed to health hazards from moulds during building repairs.

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Removal and clean-up for non-toxic moulds

The moulds most commonly seen on surfaces around the house are generally not toxic. To remove them, wash the surface with warm water and household detergent, using a cloth or scrubbing brush depending on the surface. Rinse with clean water and allow the surface to dry thoroughly.

If you wish you can then disinfect or sanitise the surface by repeated treatments with methylated spirits, but ensure the area is well ventilated.

Mould may be removed from fabrics by washing.

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Stachybotrys chartarum

Some types of moulds produce toxic compounds. Stachybotrys chartarum is a toxic mould that is associated with leaking buildings in New Zealand in recent years. The mould is caused by leaks that originate outside the building and from leaks within wet areas in buildings.

Stachybotrys is a greenish-black mould that grows on materials that contain cellulose such as wood fibreboard, fibre-cement, the paper lining of gypsum board, kraft paper wall and roof underlays, wallpaper and timber, when the material is subject to wetting.

Finding Stachybotrys in a building does not immediately mean that the building occupants have been exposed to allergens or toxins. While Stachybotrys is growing, a wet slime covers the spores, preventing them from becoming airborne. Exposure will only occur when the mould has died and dried up.

If you are working where Stachybotrys is suspected, investigate from outside, if possible, by removing a small portion of lining to determine the type of mould present.

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Testing for Stachybotrys

If any black mould is found, it is recommended that it be tested to determine if it is Stachybotrys chartarum. Carefully take a sample by the following process:

  1. Work with a mask or breathing filter and disposable gloves.
  2. Ensure that no skin is exposed.
  3. Place a strip of clear adhesive tape over the mould and press firmly. Around 100 mm will be long enough – the important thing is to make sure that what is being sampled by the tape is representative of the discolouration on the building material surface.
  4. Remove the tape and place onto non-stick baking paper. Fold the paper around the tape and place in a plastic bag.
  5. Securely seal the bag.
  6. Send the sample to a testing laboratory such as Biodet Services Ltd (, Airlab Ltd ( or Plant Diagnostics (

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Removing and cleaning up procedures for toxic moulds

When toxic mould is found, employing a specialist contractor to carry out the removal is recommended.

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