Dealing with mould

What is mould?

The air is full of all kinds of fungal spores. These spores can be carried by air currents and deposited on items or surfaces. In certain conditions, the spores germinate and grow into fungi. 

Mould is just one type of fungi. It can be detected by the presence of powdery material, multicoloured pigmentation, staining or a musty odour. Mould can be extremely destructive to library materials, causing weakening of paper, vellum and leather and loss of text or image.

Health issues

Some moulds can cause lung, skin and eye irritation and people can have different sensitivities. Therefore, safe handling of affected material is essential. Anyone who suffers from allergies, asthma or respiratory problems should not treat mould outbreaks. 

Safety precautions for handling include: 

• use personal protective equipment, which includes disposable gloves, HEPA filter or other respirator suitable for mould filtration, and protective clothing such as an apron or lab coat or Tyvek coveralls 
• washing hands, face and clothing before and after handling 
• disposing of contaminated gear and equipment (where appropriate) after handling 
• avoiding extensive handling — the longer you are exposed to mould the greater the chance of developing sensitivities 
• be aware that fungicides and biocides can be a health hazard and must be used in accordance with very strict rules and regulations 
• seek professional help if an outbreak is discovered in a large portion of the collection, as a large mould outbreak can pose a significant health risk — refer to the AICCM Conservators in Private Practice or search online for professional assistance. 

How to treat a mould outbreak 

• Assess how many items are affected and whether you should consult a conservator or pest control company. Contact a conservator if the material is valuable or fragile. Conservators have the skills to strengthen or repair items and may be able to reduce staining. If you cannot treat the mould-affected material in a timely manner, consider freezing the items. 
• Isolate the affected material. Place it in a plastic bag, seal and move it to a separate area that is clean, cool and dry, with good air circulation. Isolating the material will prevent the mould spreading to nearby items. 
• Dry out any wet material to stop the mould from growing further. 
  • Line a work surface with paper that can be thrown away. 
  • Take the material out of the plastic bag and place on the paper. Use a fan to assist the drying process. Ensure the windows and doors are open, so the spores are released outside. Dehumidifiers can assist in removing excess moisture in the air. 
  • You can also place the material outside in the sun for up to 10 minutes. Limit time to 10 minutes as the heat and light can cause fading and degradation. 
  • For more detailed instructions for drying wet books, read the Library’s fact sheet. 
• Use a soft brush (like a shaving brush) to remove the mould when the material is dry. Brush the material away from yourself into a vacuum fitted with a HEPA filter, or towards an open window, or outside. Seal vacuum bags and disposable equipment in a plastic bag when finished, and dispose outside in the garbage bin. 
• Clean the infected storage areas before packing or reshelving. Wipe down surfaces using household bleach prepared according to the label. Ensure the area is completely dry before reshelving material. 
• Make sure the conditions that supported the mould growth have changed. See the following section below. 

How to help prevent mould returning

• Keep storage areas clean: free of dirt, dust and organic debris, which these provide nutrients for mould growth. Items can be cleaned gently with a soft brush (fragile items should be treated by a conservator).
• Ensure your storage environment is cool, dry and stable, with good air circulation as mould needs moisture and warm temperatures to survive.
• Regularly inspect the area for evidence of mould activity. This will allow you to catch an infestation before it becomes large.
• Do not pack or shelve books too tightly, allowing air to circulate.
• Do not shelve books directly against an outside wall. Due to temperature and humidity differences between inside and outside environments, moisture may develop along walls and cause mould growth.

Further information

• Heritage Eaters: Insects and Fungi in Heritage Collections by Mary-Lou Florian, 1997, James and James, London.
• A Guide to Museum Pest Control, Lynda A Zycherman (ed), 1988, Foundation of the American Institute for Conservation of Historic and Artistic Works and the Association of Systematics Collections, Washington.
• The British Library – National Preservation Office Leaflets. ‘Prevention and Treatment of Mould Outbreaks in Collections’.
• The British Library – Preservation guides. ‘Salvaging library and archive collections’.
• NEDCC – Emergency Salvage of Moldy Books and Paper.
• Australian Institute for the Conservation of Cultural Materials 

Conservation advice 

If you have further questions or would like specific advice about conservation, please contact us through Ask a Librarian

We are unable to give advice on the conservation treatment of heritage items. We recommend you contact a professional conservator, who can assess each item and recommend options. A conservator will charge a fee.