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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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.

Do not carry out demolition with a crowbar as this will spread the spores.

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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 Stachybotryschartarum. 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. With a strip of clear adhesive tape about 100 mm long, place the tape over the mould and press firmly.
  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, it usually affects a significant area of the building and employing a specialist contractor to carry out the removal is recommended.

For small areas, the mould may be removed provided the workers undertaking the removal follow these procedures:

  • Seal off the space from other parts of the building by taping up all openings.
  • Wear a respirator with a P1 filter (minimum protection).
  • Wear protective clothing that is disposable or easily washable.
  • Remove any materials from which the mould cannot be removed such as wallpaper, timber products, ceiling tiles, gypsum board, carpet, drapes and furniture (carpet that is contaminated may be difficult to clean completely).
  • Place removed materials in plastic bags that can be sealed.
  • For materials such as glass, plastic and metal from which the mould can be removed completely, clean the affected area using hot water and chlorine bleach, then rinse and allow to dry completely.
  • Use a stiff brush on rough or uneven surfaces.
  • On completion, thoroughly vacuum all surfaces of the sealed area using a vacuum with a fine particulate (HEPA) filter. Once this is done, the room seals can be removed.

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