Mold control and prevention in libraries

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An example of mold damage

Mold prevention is a conservation activity that is performed in libraries to protect books and other materials from deterioration caused by mold growth. Mold prevention consists of different methods, such as chemical treatments, careful environmental control, and manual cleaning. Preservationists use one or a combination of these methods to combat mold spores in library collections.

Due to its resilient nature, mold prevention has become an important activity among preservation librarians. Mold reproduces by releasing spores into the air. It becomes active after being in a dormant state and responds to fluctuating temperature, air flow, and humidity within the surrounding environment. Library holdings have been deemed vulnerable since mold digests paper and other organic materials that collection items consist of. Moisture in the atmosphere contributes to irreparable damage caused by mold growth.[1]


Mold is a generic term for a specific type of fungi. Since there are so many species of mold, their appearance varies in color and growth habit [1]. In general, active mold has a musty odor and appears fuzzy, slimy, or damp. Inactive mold looks dry and powdery [2]. Mold propagates via spores, which are always present in the environment. Mold spores can be transferred to an object by mechanical instruments or air circulation. When spores attach to another organism, and the environment is favorable, they begin to germinate. Mold produce mycelium which growth pattern resembles cobwebs. Mycelium allows the mold to obtain food and nutrients through the host. Inevitably, the mycelium produces spore sacs and release new spores into the air [3]. Eventually the spores land on new material, and the reproductive cycle begins again. Identifying mold can be a challenge, because some species resemble dust, dirt, or spiderwebs. In addition, staining caused by mold can be confused with water damage. Ultraviolet light and magnification are two tools to aid in identifying mold on library collections [4]. Poor air circulation, moisture, high temperatures, and environmental humidity are the main causes of mold outbreaks in library collections. When the temperature is above 70 degrees Fahrenheit and the relative humidity is above 55 percent, mold begins to develop [5]. Collections kept in basements or uncontrolled environments are most likely to be impacted by a mold outbreak [2]. Mold is a dangerous library pest because of the damage it causes to the collections. Mold eats paper and books; these objects provide the fungi a source of nutrition. Mold feeds on cloth, leather, glues, adhesives, cellulose starch and starches in the sizing. Frequently, mold is noticed on the bindings long before it begins on the text blocks . By feeding on books, mold can cause the paper to become thin, soft, or spongy. Images and decorative elements can be completely destroyed or, at the very least, become stained. Beyond the collection, mold can cause harm to anyone who becomes exposed. Especially to those who have allergies or suffer from respiratory problems such as asthma. Some mold species can irritate other parts of the body through prolonged exposure. Closed areas with germinating mold can lead to damage of the lungs, mucous membrane, cornea, respiratory tract, stomach, and intestines . In some cases, protective clothing is necessary when handling mold found on library collections.

Impact on Materials[edit]

Mold is harmful to materials and can cause mold health issues in humans. When a library collection experiences a mold outbreak, actions need to be taken to ensure preservation of both materials and the good health of the humans involved. When a book or paper becomes moldy, the fungi will digest its food source, paper and cloth (such as book covers and bindings), in order to survive. This process stains and destroys books, papers, and other library collections over time.[6] During their growth mold and mildew produce citric, gluconic, oxalic, or other organic acids that can damage paper, leather, cloth, etc. They also at times produce color bodies, leading to staining which is difficult to remove.[7] Mold will continually grow until it uses up its food source, which means a library collection could be totally consumed. Unless every mold spore is treated, the issue will just return. Mold's enduring nature makes treatment difficult and prevention all the more necessary.


Conservation staff drying mold-damaged materials

The only way to control mold is by altering conditions conducive to its growth.[8] The generally accepted threshold for mold growth is about 15% moisture content. The predominant cause of mold is excess water. Excess water can come from liquid water, as a result of leaks, or water vapor, as a result of high relative humidity due to improper storage, faulty humidifiers, or HVAC malfunctions. While most research shows that fungal growth is most prevalent in conditions in which relative humidity is above 60%, humidity levels below this threshold alone will not prevent mold growth, given the fact that favorable germination environments vary from species to species, mold is often a persistent threat to many collections.[9]

Environmental Controls[edit]

Many libraries monitor a building's atmosphere through the use of HVAC systems. These built in ventilation systems help to combat mold growth that occurs as a result of relative humidity levels greater than 65% and temperature greater than 70° Fahrenheit, as well poor air circulation [10]. Proper use and monitoring of HVAC systems can help to prevent mold problems before they occur. Air ventilation removes existing mold spores from the air and keeps the atmosphere relatively dry and cool. Effective HVAC systems have good system design as well as the ability to provide environmental control over entire building areas. Proper maintenance of equipment also lowers the chances that issues will arise due to system outages .[11] At 70° Fahrenheit and 50% relative humidity, the equilibrium moisture content of the environment would be 9.2%, low enough to prevent mold growth. However, proper air flow and air exchange is required to effectively disrupt the boundary layers of air around room contents, which can have high water vapor levels within the surrounding dry air and promote mold amplification.

Manual solutions[edit]

Manual methods such as HEPA filtered vacuuming serve as a backup to eliminating mold via environmental control. HEPA vacuums possess air filters that do not allow mold to be spread into the air again. Installing drying fans, dry wiping books and surrounding furniture, as well as air ducts and shelves also help to prevent further infestations. In extreme cases, some books and items are discarded to protect the rest of the collection from being affected. These preservation activities are provided by available library staff or hired contractors.[12]


Proper storage practices can be effective in preventing mold growth. Storing materials away from exterior walls and damp areas like basements can reduce the risk of mold growth.[13] In addition, the use of desiccants can control humidity inside enclosed containers.[14]

Safe Handling[edit]

Proper handling of affected or damaged materials prevents mold from spreading. Because mold spores are released into the air, it is recommended to wear an NIOSH-rated respirator before coming into contact with affected materials.[15] Nitrile gloves protect the skin from contact with mold.[16] In extreme cases, a full-body hazmat suit may be required. Materials must always be treated on a surface that can be cleaned with bleach or on neutral, disposable materials such as unprinted newsprint.


Mold spores are always present in the environment and when conditions are favorable, mold will occur [17] . Regular monitoring of the collection through visual inspection and environmental controls is essential to prevent an outbreak.

Mold leaves a visual indication of its presence. Though mold can be any color, gray and black spots coupled with a musty odor can indicate the presence of mold.[18] . Books with these indicators can be isolated and treatment steps can be implemented. Books in the surrounding area can be monitored in case of further infestation. Presence of water/condensation and dust are other factors to look out for that can encourage mold growth. Regular cleaning and inspections will help monitor for mold growth.

Control and regular monitoring of temperature and humidity levels is vital to prevent mold growth. Guidelines suggest that temperatures be maintained between 65°-70° Fahrenheit and relative humidity between 45%-65%.[19]. HVAC systems can be utilized and monitored to ensure these levels are maintained. Temperature and humidity values can be systematically measured and recorded to document conditions, to alert of severe fluctuations, and to indicate the functionality of the climate control systems.[20]. The systems themselves can be regularly checked for accuracy and functionality.

Treatments for Mold Damage[edit]

Chemical Treatments[edit]

Preservation librarians use a number of different chemicals to prevent the growth of mold spores. Chemical compounds such as ethylene oxide, thymol, and orthophenyl phenol are regularly used.[21] Chlorine dioxide is a chemical that is growing in popularity due its safety level for library employees and patrons. These chemicals act as effective sporicides in a variety of library settings. They are applied on books and surrounding shelves by manual wiping or using chlorine packets that release the chemicals in gaseous form into the air.[22]

Chemical treatments are often used in enclosed storage areas with little air circulation. They are also used to deal with emergency situations involving mold outbreaks caused by pipe leaks in buildings. In 2000, the University of Oklahoma Libraries conducted an evaluation of the effects of chlorine packets on mold growth. Paper items that had been exposed to the substance showed lower overall pH levels than items that had not been treated. Although long-term effects of chemical treatments on paper permanence and other library materials have not been documented, libraries use this newer method of controlling mold in the stacks.[23]

Freeze Drying and UV Light[edit]

Freeze drying or ultraviolet light exposure are other ways to inhibit mold growth, although they do not kill mold spores permanently. Eliminating mold through these methods is challenging due to paper degradation caused by light exposure over time. There are also some mold species that have preferences for colder temperatures. Freezing and UV exposure are used as a temporary means to stop mold from spreading throughout library collections.[24]

See also[edit]


  1. ^ Baker, Whitney. "Preservation Perspectives: Mold in the Stacks: A Universal Problem. Kentucky Libraries. 65(3)(Summer 2001):20-22.
  2. ^ Brown, Karen E.K. (November 13, 2013). "Mold in the Library: Prevention and Response" (PDF). University Libraries University at Albany State University of New York. University Libraries, University at Albany. Retrieved November 8, 2019.
  3. ^ "EMERGENCY MANAGEMENT: 3.8 Emergency Salvage of Moldy Books and Paper". NEDCC website. Northeast Document Conservation Center(NEDCC). Retrieved November 8, 2019.
  4. ^ Brown, Karen E.K. (November 13, 2013). "Mold in the Library: Prevention and Response" (PDF). University Libraries University at Albany State University of New York. University Libraries, University at Albany. Retrieved November 8, 2019.
  5. ^ Nyberg, Sarah (November 1987). "Invasion of the Giant Mold Spore". Conservation OnLine (CoOL). Solinet Preservation Leaflets. Retrieved November 8, 2019.
  6. ^ "Mold In Libraries Causes Significant Indoor Air Quality Problems". Extract All. Retrieved 2019-11-01.
  7. ^ "Mold : Preservation Resources : Minnesota Library Storage (MLAC) : Products & Services : Minitex". Retrieved 2019-11-01.
  8. ^ "Mold | Library Preservation and Conservation Tutorial". Retrieved 2019-11-01.
  9. ^ "Mold, Pest, and Water Damage Response – Staff Website – U of I Library". Retrieved 2019-11-01.
  10. ^ Nyberg, Sandra. "Invasion of the Giant Mold Spore". Retrieved 1 November 2019.
  11. ^ Brown, Dors R. "Collection Disaster: Mold in the Stacks." College & Research Libraries News. 64(5) (2003):304-306.
  12. ^ Alleman, Steve. "Coping with an Outbreak of Mold." LLA Bulletin. 61(4) (Spring 1999):217-220.
  13. ^ "Managing a Mold Invasion |" (PDF). Retrieved 2019-11-01.
  14. ^ "Mold | Library Preservation and Conservation Tutorial". Retrieved 2019-11-01.
  15. ^ Stauderman, Sarah (2013-02-21). "I've got mold in my files". Smithsonian Institution Archives. Retrieved 2019-11-03.
  16. ^ "Gloves or No Gloves? On the Proper Handling of Rare Books & Manuscripts". Portland State University Library. 2015-06-04. Retrieved 2019-11-03.
  17. ^ Livingston, Preston. "Mold Prevention and Remediation in a Library Environment". Questia. Retrieved 1 November 2019.
  18. ^ "Mold : Preservation Resources : Minnesota Library Storage (MLAC) : Products & Services : Minitex". Retrieved 2019-11-01.
  19. ^ Nyberg, Sandra. "Invasion of the Giant Mold Spore". Retrieved 1 November 2019.
  20. ^ Ogden, Sherelyn. "2.1 Temperature, Relative Humidity, Light, and Air Quality: Basic Guidelines for Preservation". Northeast Document Conservation Center. Retrieved 1 November 2019.
  21. ^ Southwell, Kristina L. "The Use of Chlorine Dioxide as a Mold Treatment and its Effect on Paper Acidity: a case study." The Journal of Academic Librarianship. 28(6) (2002): 400-405.
  22. ^ Southwell, Kristina L. "Chlorine Dioxide: a treatment for mold in libraries." Archival Products. 10(3) (2003)
  23. ^ Southwell, Kristina L. "The Use of Chlorine Dioxide as a Mold Treatment and Its Effect on Paper Acidity: a case study." The Journal of Academic Librariansip. 28(6) (2002): 400-405.
  24. ^ Baker, Whitney. "Preservation Perspectives: Mold in the Stacks: A Universal Problem." Kentucky Libraries. 65(3) (Summer 2001): 20-22.

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