Mold can be a problem for libraries and archives, especially those with faulty or non-existent HVAC systems or those that have experienced floods or leaks. Mold is a general term given to a wide variety of fungi common to most parts of the world. Mold grows through the propagation of its spores, which are always present in the air waiting for the right opportunity to germinate and develop new colonies. Wet surfaces or even high humidity can provide the necessary conditions for mold germination. The visible signs of mold result from the development of the spores into a mycelium (colony), the familiar, velvet-like surface covering. The mycelium, in turn, generates more mold spores that become airborne to continue the cycle. Mold spores and mycelia can be allergenic or toxic at any point in their development. Consequently, the treatment of mold-infected material must be handled with care to avoid inhalation or ingestion. Although not all molds are toxic to humans, any mold may produce allergic reactions. It is important to regard all infestations as possibly toxic and take the appropriate precautions (respirator, apron and gloves) when entering an infested area.

It is important to remember that mold is usually the result of high humidity and poor air circulation. Temperature is less of a factor, except, of course, as it affects relative humidity (low temperatures result in moisture condensation on surfaces). Mold can grow on any moist surface, including materials such as paper, leather, and book coverings. As it grows, it digests the substrate thereby causing stains and losses.

Detecting mold

Mold grows in conditions of high humidity, direct wetting, and poor air circulation. Sometimes mold develops in a small, isolated area within a larger space served by a generally efficient HVAC system. In this case, a survey of the area will usually reveal inadequate air circulation. In some cases, a micro-environment such as an exhibit case can be conditioned to control humidity through means of a desiccant like silica gel, which absorbs moisture and thereby reduces humidity. This approach is only effective in an enclosed system.

Mites known as book lice** ** can be a useful indicator of mold. These tiny grey/white insects inhabit the inner margins of damp books and feed on microscopic mold embedded in the paper. Hidden mold can also be detected with ultraviolet light, exposure to which causes the fungi to turn fluorescent. Mold can also be detected by the musty odor common to damp basements.

If mold is discovered, take immediate steps to discover the cause. Check for water infiltration (wet floors, ceiling, or walls). Is the HVAC functioning correctly? Does it provide the appropriate level of air flow, and are the pre-heat coil and misting unit working? Is there a structural problem causing rising damp or condensation? Did the mold come in with a new acquisition?

Preventing mold

The only way to control mold is by altering conditions conducive to its growth. For example, paper collections should not be stored in a basement with a low temperature, high humidity, little light and very low air circulation—ideal conditions for the growth of mold. Even if remedial treatment is undertaken, the material will quickly deteriorate again if returned to the environment in which the mold first developed.

When the cause has been traced, take immediate steps to remove it. Vacuum or mop up standing water, adjust the HVAC, and/or activate electric fans to speed up the circulation of air. If dehumidifiers are available, they should be employed with both HVAC and fans.

Mold is the prime enemy of film materials, attacking the surface and emulsion. If film is unprocessed and stored in a moisture-proof container, it is usually safe from mold. However, when the package is broken, mold threads or filaments develop and immediately become apparent when the film is exposed. Film left in a camera in humid conditions is especially susceptible to mold. Coating microfilm during processing is regarded as a useful preventive measure, as this reduces the risk to the emulsion layer and allows the mold to be removed before serious damage occurs. One such coating is polysulfide, developed by the Image Permanence Institute of Rochester, New York (USA).

Treating mold-infected books

In the past, various chemicals were used to “kill” mold spores, including ethylene oxide in a vacuum chamber (now effectively banned because of health concerns) and heated thymol and para-dichlobenzine (now recognized as mostly ineffective). No matter what chemicals were used to kill mold, materials would again become moldy if returned to the same environment. Chemical treatment is no longer viewed as an effective way to control mold. Instead, mold is treated by lowering humidity and increasing air circulation.

If a large number of books are wet or damp, freezing is a way of quickly stabilizing the infestation until appropriate treatment can be dispensed. The books will have to be air dried  or freeze-dried  before being treated.

The treatment of mold-infected books requires that they be taken to a well-ventilated area with electric fans to increase air movement. A good arrangement is to stand the books on edge with the boards slightly opened have a fan blow across them through an open window or to handle the books inside a running fume hood (cupboard) that is connected to a <a href="/glossary#Hepa" title=“The term for “high-efficiency particulate air (filter).” HEPA filters in vacuum cleaners and respirators, etc, remove 99.97% of particles more than 0.3 microns in size.

" class=“lexicon-term”>HEPA filter or a biohazard cabinet. Rapidly moving air will dry out the moisture and desiccate the mold spores, rendering them inactive. If possible, take the books outdoors and place in an area with a mild breeze for a short time. Ultraviolet light is harmful to library materials, so exposure to sunlight should be limited. In handling infected books, staff should wear N95 face masks or respirators and plastic or rubber gloves. Nitrile gloves (synthetic rubber) are preferred.

Once the books are dry and the mold is inactive, a HEPA filter vacuum cleaner may be used to remove as much of the inactive mold as possible from the covers of the books.

If the library does not have a HEPA filter vacuum, activated dusters (dusters with an electrostatic charge can be used. The dusters should be laid over the infected area, the mold spores gently picked up and then the dusters discarded. This procedure prevents mold spores from being released into the air. Inactive mold is potentially toxic and allergenic.

When the inactive mold has been removed, the outside of book covers can be wiped with a 7-% solution of ethyl or isopropyl alcohol. This acts as a mild solvent to remove some of the outer staining. Care must be taken not to wet the area too much.

The inside of the books can now be examined. In many cases, mold stains will be seen on the inside of the binding, near the joints and at the head and tail. The stains can be gently swabbed with ethyl or isopropyl alcohol, but it is unlikely that they will be completely removed. Although mold stains can be treated with chemical bleach, this is not recommended because bleach can cause the paper to deteriorate rapidly, especially in humid conditions, and the mold stains are likely to return.

Returning treated books

Books should not be returned to their shelf location until the space is declared completely free of mold and the cause identified and rectified. Affected surfaces in the room can be washed down with a liquid bleach solution (1 cup of bleach to 1 gallon of water), but this should be completely dry before the room is again occupied.

All cleaning supplies such as rags or sponges and filters from the HEPA vacuum should be discarded. The hoses of the vacuum should also be cleaned.

Following the return of books to the shelf, the room should be inspected periodically to ensure that mold has not returned. HVAC components should be checked, especially in vent areas, and HVAC filters changed on a regular basis. In the absence of HVAC, ensure that air circulation is improved.

What not to do

  • Do not increase the temperature in the hopes of drying out the materials. This may encourage mold growth. Rather, focus on lowering the humidity through increased air circulation and use of a de-humidifier.

  • Do not spray or swab the books with bleach or cleaning agents. This can cause severe damage to the books.

  • Do not use a chemical fumigant without first checking to see if it is toxic. It will be necessary to first identify the mold to make sure the fumigant will be effective.

  • Do not inhale or ingest mold spores. Wear personal protective equipment (PPE) such as gloves, respirators and aprons.

Mold damage to non-book materials

Prints, maps, framed items, and other artwork needs to be handled with great care, as careless vacuuming or dusting can damage fragile surfaces. A useful mold removal method is to place a piece of fiberglass insect screening over the piece, then vacuum through the screen to remove as much of the inactive mold as possible. If you are working outdoors and wearing a respirator, a soft brush may be employed to gently remove the mold. Take care not to grind the spores into the medium or the paper fibers. If framed materials show signs of mold on the inside of the frame enclosure, the artifact should be unframed, treated, and reframed using new matting and a frame that has been thoroughly cleaned and dried.