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Mould in libraries and museums

Mold on books

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The only way to reduce the threat of mould in a library or museum is to maintain an environment that is not hospitable for the germination of mould spores.

Temperature should be between 20-22°C and the relative humidity 65% or less. It is important that the air conditioning system (HVAC) be kept on 24 hours a day, 7 days a week. Fluctuations in the temperature and humidity are the cause of many serious mould outbreaks.

Mould and mildew are generic terms for various types of fungi. Fungi produce enormous quantities of microscopic spores. These spores are always present in the environment and are spread by air currents. When these spores find a hospitable environment they will germinate.

If small patches of germinating spores are ignored they will become a mould bloom or outbreak. A mould bloom is basically millions of fungi producing enormous quantities of spores.

Causes of mould growth

Moisture is required for spores to germinate.
  • Mould will grow on any organic host material that offers suitable nutrients including paper, adhesives, book bindings, microfilm, slides, videotapes, dust, etc.

  • Books and paper provide a perfect host for mould to germinate. They are hygroscopic and absorb and hold moisture.

  • A mould bloom in a library indicates that there has been an increase in relative humidity. This could be caused by any number of things.

There are many negative aspects to a mould outbreak. Firstly, health concerns. All moulds can result in serious health concerns including respiratory problems, skin and eye irritations and infections.

Mould spores enter the body by inhalation and through small breaks in the skin. There are also costs associated with mould outbreaks.

There is the cost of the clean-up, the lack of access to the facility, the replacement costs of damaged materials.

Damage to materials includes staining of book bindings and weakening of paper. It can completely digest the image layer of photos, slides, and microfilm.

Combating mould

A controlled environment is essential to preventing large-scale outbreaks of mould. To achieve this, the institution requires:
  • Moderate, constant temperature (20-22°C). Turning off air conditioning causes fluctuations in temperature and the relative humidity to increase.

  • Low, constant relative humidity (if possible less than 60%, max. 65%). Reheat systems can be installed to remove moisture from outside air brought in through the HVAC. Room dehumidifiers need to be emptied or they can re-introduce moisture into air. They can also be a source of water leaks.

  • Good air circulation. Fans can be installed to improve air circulation.

  • Good housekeeping. Books and library materials should be regularly dusted.

Mould will stop growing and become inactive or dormant in a controlled environment, however the spores will remain viable on the host material. Increases in relative humidity or other moisture will facilitate a mould bloom. The use of ultraviolet units will inhibit the spread of spores.

Mould will stop growing and become inactive or dormant in a controlled environment.

Cleaning affected books and materials

Fungicides are not recommended for treating mould in libraries due to the concerns about both toxicity and long-term effects on collection materials.

Also these compounds provide no residual protection. The only way to stop mould is to control relative humidity and clean materials.

  • Chemicals used to clean walls (e.g. Lysol, Clorox) are not appropriate to use on books.

  • Vacuum with HEPA filter should be used to prevent spreading or further embedding the mould spores.

  • Vacuum binding, spine, and text block.

  • To remove additional mould residue from bindings use a commercial wipe with a small amount of isopropyl alcohol. Always test a corner of the binding to be sure the alcohol will not stain or damage the binding.

  • Air circulation is important. After you have cleaned mould off of materials, install fans in area.

  • If you have a small outbreak, you could take your materials outside on a dry, sunny day to vacuum them. A brief exposure to ultraviolet rays will kill mould spores. However, ultraviolet can cause long-term, irreversible damage to library materials. Indoors it is essential to use ultra violet units that are shielded whereby only the air is irradiated.

  • Clean all work surfaces, including book trucks, shelves, and walls thoroughly. Vacuum then wipe all surfaces with a Lysol type solution.

  • Clean or remove carpets and drapes in area.

  • Clean and disinfect A/C coils, filters, drip pan, and ductwork of the HVAC system.

  • Monitor library: Regularly check stacks for evidence of mould, especially during the rainy season.

  • Monitor temperature and humidity daily in problem areas. A hygrothermograph will record fluctuations in temperature and humidity over a 24-hour period.