Conservation issues: treating mold or mildew

Mold and mildew are both types of fungus. Mold and mildew spores are always present in the air and on objects. The spores only need an appropriate temperature and moisture content in the environment to grow thread-like filament called a hyphae. Using the object it is growing on as a food source, the hyphae form a mass, called a mycelium, and begins to produce more spores. At maturity, spore sacs burst and release the new spores, which eventually land on other material and begin the reproductive cycle again. Cellulose-based materials, such as cotton, linen, and wood (which are all the materials paper is made from), and proteinaceous materials such as leather (used in book bindings) are particularly desirable food sources for mold and mildew spores. Therefore, to protect library materials, the most important thing to do is to maintain an appropriate temperature and relative humidity level in the collection areas.

Even in an environment that is maintained properly, regular inspections for mold should be done in order to quickly contain any possible outbreaks. The first sign of mold or mildew is often the characteristic musty smell associated with an infestation. Careful visual examinations will often located spots or stains on library materials. Another way to inspect for mold and mildew is by using UV lights. Mold and mildew is luminescent in such lighting.

When mold or mildew is found, the first thing to do is to identify if it is an active or inactive infestation. An active infestation will smear and be moist when touched. And inactive infestation will appear powdery. The second thing to do is to isolate the infected materials. Limited numbers of materials can be sealed in a polyethylene bag or enclosed in polyethylene sheeting. If whole areas are infested, they should be quarantined. These measures will prevent the spread of mold or mildew spores.

Fixing a mold or mildew problem has two steps: treating the infected materials and locating/eliminating the source of the problem. To treat infected materials, first the mold or mildew must be inactive. This can be accomplished by freezing the material the infestation is growing on. Once the mold or mildew is inactive, vacuuming is the best way to remove spores. For this purpose, a vacuum cleaner which will not exhaust the spores back out into the room, such as a vacuum fitted with a HEPA filter, is recommended. A wet vacuum, filled with a solution of water and Lysol or bleach to kill the mold or mildew can also be used, but the material must then be thoroughly dried.

Once the mold or mildew is removed, to eliminate the associated odor from a small number of items, place an odor absorbent material, such as baking soda, charcoal briquettes (without injected lighter fluid), or kitty litter into a small container and seal the materials, along with this container, into a larger container. The baking soda, charcoal or kitty litter will absorb the smell over the course of several weeks. For larger numbers of items, a freeze drying company should be contacted for this service.

To treat the source of the infestation, vacuum the floor, walls, ceiling, and shelving units in the affected area. Then ensure the temperature and humidity levels are correct. Inspect for water leaks in the area from broken/poorly sealed windows or from air conditioning units. Check for moisture on the outside walls. Also check the coils of the air conditioning unit for mold or mildew--it might be blowing spores throughout the environment.

Remember: preventing mold and mildew through vigilant monitoring of environmental conditions is far preferable to treating outbreaks!


Nyberg, Sandra.(1987). The Invasion of the Giant Spore. SOLINET Preservation Program, Leaflet Number 5, 1. Available http://palimpsest.stanford.edu/byauth/nyberg/spore.html

Alabama Deprtment of Archives and History Government Records Division. (2003). Responding to a Mold or Mildew Outbreak. Available http://www.archives.state.al.us/ol_pubs/mold03.pdf

The National Archives. (1993). Mold and Mildew: Prevention of Microorganism Growth In Museum Collections. Available http://www.archives.gov/preservation/conservation/mold-prevention.html

For more information: http://palimpsest.stanford.edu/bytopic/mold/