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Preservation Department



Mold Damage



The only real way to reduce the threat of mold in a library is to maintain an environment that is not hospitable for the germination of mold spores. The temperature should be 68-72 degrees F, and the relative humidity of 65% or less. It is important that the air conditioning system be kept on 24 hours a day, 7 days a week. Fluctuations in the temperature and humidity are the cause of many serious mold outbreaks.


What is mold?

Mold and mildew are generic terms for various types of fungi, which are spread by air currents and will germinate if they find a hospitable environment. Once small patches of germinating spores appear, they will lead to a mold bloom unless measures are taken to contain the outbreak.


What causes mold to grow?

moldy booksMold will grow on any organic host material that offers suitable nutrients, including paper, adhesives, bookbindings, microfilm, slides, videotapes, dust, etc.  Books and paper especially provide a perfect host for mold to germinate since they are hygroscopic and absorb and hold moisture.
A mold bloom in a library indicates that there has been an increase in relative humidity. This could be caused by any number of things:
  • Changes in the natural environment (e.g. rainy season in Hawai'i)
  • Fluctuation in interior environment (e.g. turning off the AC at the end of the day and on weekends)
  • Construction/building disasters (e.g. roofing, leaks)
  • Natural disasters (e.g. floods, hurricanes)

How to prevent mold?

Controlled environment is essential to preventing large-scale outbreaks of mold. This means:
  • Moderate, constant temperature (68-72 degrees F). 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%). Room dehumidifiers need to be emptied or they can re-introduce moisture into air.
  • Good air circulation. Fans can be installed to improve air circulation.
  • Good Housekeeping. Dust books and library materials regularly.
  • Regularly monitor the library for mold.

How to combat a mold outbreak?

really moldy books
First, verify that the problem is mold (stains from earlier mold damage or silverfish damage can resemble a mold outbreak). If mold is confirmed, respond immediately and organize a team to cleanup the mold. If possible, isolate contaminated materials by bagging them.

Fungicides are not recommended for treating mold in libraries due to the concerns about both toxicity and long-term effects on collection materials. Household chemicals (e.g. Lysol, Clorox) are also not appropriate to use on books.

Vacuum books (binding, spine) as well as book trucks, shelves, and other work surfaces. Using a vacuum with HEPA filter will prevent spreading or further embedding the mold spores. Wipe all surfaces and walls with householf cleaner (e.g. Simple Green) and clean (or remove) any carpets or drapes in the affected area.

Installing fans after the cleaning process is completed can improve air circulations and prevent mold spores from returning.


For more information

and links on mold prevention and management visit the Pest & Mold Resources page.


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