Remedies: mould

Mould is common when moisture is present, and can be harmful to health.

Presence of mould

Where moisture levels have been high or there has been a leak, mould may initially be seen on painted and papered walls and ceilings, and on fabrics. Mould may also be found when structural elements are exposed during demolition and renovation work, inside walls, under the floor or behind linings.

Moulds are fungi and require moisture and a food source to grow. They reproduce by releasing vast numbers of tiny spores. There is no effective way of eliminating mould, but it can be controlled by controlling indoor moisture levels.

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

Appropriate precautions must be taken to ensure that building occupants and anyone working on the building are not exposed to health hazards from mould during renovation or repair work.

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Stachybotrys chartarum

Some types of moulds produce toxic compounds. Stachybotrys chartarum is a toxic mould that is associated with the leaking building problems that New Zealand has experienced in recent years. Leaks originating from outside the building and from wet areas in the building provide the environment suitable for Stachybotrys to grow.

Stachybotrys is a greenish-black mould that grows on materials containing cellulose such as wood fibreboard, fibre-cement, the lining paper of gypsum board, kraft paper wall and roof underlays, wallpaper and timber when it is subject to repeated wetting. It is almost always within the wall cavity, not within the rooms.

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

Testing for Stachybotrys

If Stachybotrys is suspected, investigate from outside if possible, by carefully removing a small portion of cladding (or lining, if access is easier from the inside) so a sample of the mould can be taken for testing. Wear a mask or breathing filter and disposable gloves and ensure that no skin is exposed.

Follow the procedure described below to take a sample:

  • Take a strip of clear adhesive tape about 100 mm long, place it over the mould and press firmly.
  • Remove the tape and place onto non-stick baking paper. Fold the paper around the tape and place in a plastic bag.
  • Securely seal the bag.
  • Send the sample to a testing laboratory such as Biodet Services Ltd (, Airlab Ltd ( or or Plant Diagnostics (

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Removal and clean-up procedures for toxic moulds

If toxic mould is found to affect a significant area of the building, a specialist contractor should be employed to carry out the removal.

Small areas may be done without using a specialist contractor but precautions must be taken. Wear a respirator with a P1 filter (minimum protection) and wear protective clothing that is disposable or can easily be washed.

Follow the procedure described below to remove the mould:

  1. Seal off the space from other parts of the building by taping up all openings.
  2. Remove all materials from which the mould cannot be removed such as wallpaper, timber products, ceiling tiles, gypsum board, drapes, furniture and carpet – carpet that is contaminated may be difficult to clean completely.
  3. Place all removed materials in plastic bags that can be sealed.
  4. Clean the affected area of materials such as glass, plastic and metal, from which the mould can be removed using hot water and chlorine bleach. Use a stiff brush on rough or uneven surfaces.
  5. Rinse and allow to dry completely.
  6. Vacuum all surfaces of the sealed area thoroughly using a vacuum with a fine particulate (HEPA) filter.
  7. Remove the room seals on completion.


Removal and clean-up procedures for non-toxic moulds

Non-toxic moulds can be removed by thoroughly cleaning the surfaces with either a proprietary mould remover or a 25% household bleach solution. Surfaces should be allowed to dry thoroughly. Mould may be removed from fabrics by washing.