Treatment of Mold Outbreaks / Water Intrusion (edited)     Home Up

     by Mary Wood Lee -- June 1988

See Also:
Mold & Mildew Summary
Understanding Mold
Prevention of Mold
Storage Materials

The most effective treatment in all but the most extreme cases is modification of the environment and removal of the mold growth from the affected item. Most mold outbreaks, if dealt with promptly, can be controlled without recourse to biocides. Fumigants should be necessary only in the most extreme cases, for example, a prolonged delay in beginning treatment following a major disaster. Even in this worst case scenario, options such as freezing, if available, may eliminate the need for fumigants entirely.
Selection of the appropriate treatment should be based on an analysis of the problem and the nature of the material. Different approaches will be required for different media, and different levels of treatment will be necessary depending on the size of the outbreak.

A variety of treatments will be discussed, many of them incorporating some form of vacuuming. It may be that the vacuum is one of the most important tools in the prevention and treatment of mold growth in tropical climates. The use of vacuum cleaners or vacuum aspirators to remove mold growth from the surface of items, is, in the author's view, preferable to other treatments currently available. The vacuum removes all elements of the colony (spores, conidiophores, and mycelium) and packages them neatly for disposal. It is non-toxic, and if used properly, does no structural or chemical damage to the item being treated. Vacuums are readily available everywhere, and are economical to operate. Even when electricity is not available, they can be operated with battery packs. The major disadvantage of vacuuming is that it requires handling each book individually and treatment is therefore labor intensive.

The equipment needed for the removal of mold growth as recommended in this study is quite basic, and should be readily available in most areas. It includes:

- Portable vacuum cleaner with flexible hose and crevice tool for the removal of mold from book covers.

- Mini-vac for the removal of mold from paper surfaces.

- Powdered art gum eraser for cleaning the surface of paper too brittle to be vacuumed.

- Soft dusting brushes for the removal of art gum the surface of paper.

- Watercolor brushes with a fine point for removing mold from pastels and other fragile surfaces.

- Fine pointed surgical tweezers which may also be used for removing mold from the surface of delicate materials.

This section will describe treatment for small, moderate and major mold outbreaks, and provide suggestions for treatment of specific categories of materials, including books, unbound paper, photographic materials and the general area affected. Readers should augment this information with materials included in the recommended literature on procedures for dealing with major disasters.

Small outbreaks - localized high relative humidity

A small outbreak is here defined as the occurrence of mold on not more than a few hundred items. In a small outbreak, the mold affects only selected items or a specific area of the building, the materials are not actually wet, the mold growth having resulted from changes in the environment (usually an increase in the ambient relative humidity).

Treatment and modification of the environment should begin as soon as the mold is discovered. The delay of even a few days may turn a minor outbreak affecting only a few hundred items into a moderate outbreak affecting a few thousand.


Small outbreaks of mold on bound materials are usually confined to the covers of books. They most often begin on the spine of the book, less frequently on the boards and around the turn-ins. Mold that occurs on the surface of book pages should be treated according to the recommendations for unbound materials below.

Mold growth should be removed from the covers of books by vacuuming, using small hand held or canister type vacuums with flexible hoses. The long slender attachment designed for cleaning crevices should be used, not the short round attachment with a brush. The brush attachment is not recommended as it will catch and hold the spores, conidiophores, and mycelium and prevent them from being drawn into the vacuum. The crevice tool will more effectively remove the growth by concentrating the pull of the vacuum on a relatively restricted surface area. A low power vacuum is best. One to one and a half horsepower is more than adequate. Large shop vacuums or wet/dry vacuums should not be used in the treatment of individual items.

The following procedures are recommended as a general guide:

- The affected books and the surrounding area should be examined to determine which materials are affected and why.

- Temperature and relative humidity readings should be taken in the immediate area. These readings should be compared to records for that area to pinpoint any changes. If records do not exist, readings should be taken in unaffected areas near by. As soon as the nature of the problems is determined corrective measures to modify the environment should begin.

- Affected books should be handled as little as possible during removal from the stacks. Touching the mold will transfer the spores to worker's hands and press the mycelium down onto the book surface. Books should be placed on a book truck, standing upright as they did on the shelves. They should not be stacked or carried by hand, as this will spread spores and compact the mold colonies.

- Treatment of the affected books should be carried out in a work area where there is adequate light for close examination. As each book is removed from the truck, the mold should be vacuumed from the surface. The entire book should be cleaned thoroughly. The mycelium may be present beyond the obviously affected area, but not visible.

- If the book has a hollow spine, the back of the book block should be examined to determine whether there is mold growth inside the spine. A flashlight may be used to see down into the middle portion of the spine. If there is evidence of mold growth on either the spine lining or the adhesive, alcohol or a mild fungicide such as Lysol (which contains orthophenyl phenol) can be used to swab the inside of the spine and the back of the book block. A cotton swab on a long stick (wooden or bamboo barbeque skewers are useful) should be used to apply the fungicide. The book should then be placed upright in an open position and allowed to dry thoroughly before the volume is closed and returned to the stacks. It is not advisable to use either alcohol or Lysol on the outer cover of the book. They may cause staining, changes in the color of the cloth, or loss of gilding. For mold on the outside of volumes, vacuuming is preferable.

- Continue to monitor the conditions in the affected area with a psychrometer or recording hygrothermograph until it has been established that the problem has been corrected and conditions have returned to normal. Do not return treated materials to the stacks until the environment has been corrected.

Unbound materials (documents, maps, works of art on paper)

Mold may occur on unbound sheets of paper exposed to a high ambient relative humidity, or on materials in enclosed spaces (such as cabinets or glazed frames) where a microclimate has developed. Mold is less likely to occur on the pages of bound materials unless they are, or have been, wet.

Since single sheets of paper are not strong enough to withstand the pull of an average vacuum cleaner without damage, variations on the procedures described above are required. Mini-vacuums designed for cleaning camera equipment, electronics and other delicate materials can be used to remove mold from the surface of documents without damage to the paper.

The following procedures are recommended:

- Affected items should be removed to a work room for treatment. If files are involved, the file folders should be placed upright in open boxes during the move.

- The procedures for monitoring the environment described above should be followed.

- Framed items should be removed from their frames and the mats and backing materials discarded. Any information on the mats or backings should be copied and retained. The glass should be cleaned thoroughly with glass cleaner or a dilute solution of household ammonia and water. The frame should be thoroughly vacuumed before reframing.

- Works of art on paper, documents and maps should be cleaned with the mini-vac or a vacuum aspirator. Both the front and back of the items should be cleaned. After vacuuming with the mini-vac, the surface of the item should be cleaned with powdered art gum eraser. The art gum residue should be brushed from the surface of the item after cleaning and should be vacuumed up with the hand held or canister vacuum.

- If an item is very brittle the surface should not be vacuumed. Instead, reversing the procedure described above, powdered art gum eraser may be used to clean the surface. Cleaning should begin at the center of the item, and proceed toward the outer edges working in all four directions. The residue should be brushed off and vacuumed up. This will not remove the growth as thoroughly as vacuuming, but will pick up most of the spores and mycelium.

- Works of art with pastel, chalk or other friable pigments should not be vacuumed. In such cases the mold must be lifted from the surface of the item using a fine pointed, stiff bristled brush. A head band magnifier or magnifying glass should be used in order to insure the removal of the mold and to prevent the disturbance of the surface. The mold picked up by the brush should be removed from the bristles after each area has been cleaned using the vacuum or mini-vac. Very fine pointed surgical tweezers may also be used to lift mold from the surface of delicate materials.

- If only the edges of file cabinet materials are involved, they can be vacuumed using the crevice tool described above. If mold growth is extensive, folders should be discarded. Information on the folder should be copied and retained with the items. The discarded folders should be placed in plastic trash bags and removed from the area. Care must be taken to insure that the removal of the mold growth is complete. If there is any doubt regarding the extent of the mold growth, each sheet should be cleaned individually with the mini-vac as described below.

- If the mold has developed-in drawers, cabinets or other confined spaces the relative humidity must be lowered before items are returned to that space. The RH can be lowered by opening the drawers and cabinets and using fans to dry the interiors. Desiccants, placed in trays at the bottom of the cabinets may also be used in lowering the RH. If desiccants are used, they should be monitored and reconditioned when exhausted. If the problem seems likely to be a recurring one, the measures taken to correct the environment may have to be continued in order to maintain it. Desiccants are the most effective means of maintaining an acceptable RH in cabinets and drawers once it has been achieved.

General area

In a relatively minor outbreak, improved air circulation is usually enough to bring down the relative humidity and lower the temperature in the immediate area. This may be accomplished by the use of fans alone, or by a combination of fans and dehumidifiers. Recurring problems may require the rearrangement of the area in order to improve air flow. The exact measures taken to correct a microclimate problem depend on the analysis of the situation at the time of the outbreak.

Moderate outbreaks - Major and prolonged periods of high humidity or minor flooding

A moderate outbreak is here defined as one involving a few hundred wet items or several thousand dry but moldy items located throughout the building. Two different courses of action are recommended depending on which of these conditions prevail.

Dry Moldy Items

For the treatment of mold resulting from prolonged periods of high humidity and affecting significant portions of the library collection, lowering the temperature and relative humidity through improved air circulation is the most viable option. Books should be vacuumed in the stacks if the number involved is too large to consider moving them to a treatment location. Cabinets and drawers should be opened and the contents vacuumed. They should remain open until the RH has reached an acceptable level and the situation is under control. Conditions should be monitored in all affected areas of the library. Any items that are felt to merit individual attention should be handled as described above in the section on minor outbreaks.

Wet Items

Detailed procedures for the salvage of large numbers of wet items has been covered in a number of publications. Two that are especially recommended are Procedures for Salvage of Water-Damaged Materials1 and An Ounce of Prevention. These recommendations should be followed for the handling and treatment of wet materials. The recommendations below will focus on the prevention of mold growth during the treatment and drying of items that are wet as a result of localized flooding.

Localized flooding may occur as a result of burst pipes, leaks in ceilings, walls or windows, or from backed up drains or flooding in the lower areas of the building. If the flooding involves water from rivers or any form of backup from drains, precautions must be taken to protect workers from possible infection and disease.


The recommendations below are intended as a general guide.

- Removal of wet items from the flooded area should be the first priority and should take place as soon as possible. Once the books have been removed, standing water should be removed. If left, it will contribute to continued high relative humidity throughout the area and may result in mold growth on items not directly affected by the flood. Water may be removed using pumps, wet/dry vacuum cleaners, or mops and buckets. Fans should be set up in order to lower the relative humidity and insure adequate air circulation.

- Wet items should be removed to a large dry area where fans can be kept in operation 24 hours a day to speed the drying and reduce the likelihood of mold growth.

- Items should be dried on tables. Drying wet books on the floor should be avoided since circulation will be worst at floor level. If the drying process takes several days, materials on the floor will be more vulnerable to insect attack, and the handling of materials and movement around the room will be more difficult.

- Items should be constantly attended during the drying process. Pages should be turned and inter-leaving materials replaced frequently in order to insure relatively uniform drying. Interleaving papers should hung up to dry if they are to be reused. If they are to be discarded, they should be placed in plastic bags and removed from the area.

- As items dry they should be removed from the treatment room. Each item should be carefully inspected to be sure that it is completely dry before it is transferred to a storage area.

- If mold has developed it should be vacuumed off the items only after they are reasonably dry. No attempt should be made to vacuum very wet materials.

- If there are too many items: for a limited staff to handle, or if there are delays in beginning the drying process for some items, freezing may be necessary.

Unbound materials

- Wet items should be removed to the drying areas as soon as possible. Unbound sheets should be treated in a separate area of the room from bound materials. This will allow better use of space and faster drying.

- Matting materials should be removed and discarded if this is possible without damaging the item. Relevant information can be copied and retained with the item. If the item is mounted overall to board, no attempt should be made to remove it from the backing unless it is obvious that the adhesive is water soluble, and the item is already partially detached. If this is the case, the backing should be removed from the item a layer at a time. Do not attempt to lift the item from the backing. If items must be dried on backing boards, they should receive special attention during the drying process, since they will dry more slowly, and the adhesive may increase the possibility of mold growth.

- Individual sheets should be spread on tables to dry and turned frequently as soon as they are dry enough to be safely handled. If space is a problem, trays can be constructed from fiberglass screening and wooden frames, and stacked, provided that there is adequate space between them to allow air circulation.

- Rolled items should be carefully unrolled after they reach the drying area. Multiple items rolled together should be carefully separated for drying.

- Care should be taken in positioning fans. They should provide good circulation but not blow directly onto drying items. Partially dry papers can be lifted and torn by the draft from an improperly positioned fan. Air movement should be constant above and below the items, but not directly on them.

- Documents in file folders may be dried upright in the folders if only the upper edges are wet. If the entire folder or the bottom fold is wet, they must be opened and the contents spread out to dry.

- Materials should be removed from the drying room as soon as they are completely dry. If there is residual mud or evidence of mold growth they should be cleaned with the mini-vac and powdered art gum as described above.

For unbound paper items affected by flooding, freezing is usually not necessary. Since they will dry more rapidly, unbound paper should be attended to immediately, and materials which will require several days or weeks to dry should be chosen for freezing. These frozen items can then be dried in smaller increments as staff and space are available.

General area

In most cases of localized flooding, the removal of standing water and the use of fans is sufficient to return the area to a functional condition. Conditions should be carefully monitored to insure that the relative humidity has returned to a safe level before items are returned. Materials should be checked frequently in the weeks after their return to the flooded area to detect any mold which may occur on items not completely dry.

Shelving and cabinets may be wiped down with alcohol or Lysol if there is evidence of mold growth on their surfaces. Sterilization of the area should be required only if the water is suspected of having been contaminated by sewage. Sterilization should be carried out by a qualified commercial fumigator, and staff and users should not return to the area until it has been thoroughly aired.

Equipment and supplies


Most of the equipment necessary for the prevention of mold growth should be readily available from a number of sources.

  • Fans

A variety of different fans may be necessary in order to effectively modify the environment and provide adequate air circulation and ventilation. Permanent installations in walls, ceilings and windows should be supplemented by portable fans which can be moved to problem areas of the building as needed. Fans are also necessary during emergencies, both to maintain air circulation in drying and treatment areas and to increase air circulation in flooded areas during the removal of water damaged materials. Libraries in tropical areas cannot have too many fans.

  • Vacuum Cleaners

For routine cleaning and maintenance of collections, portable canister or hand held vacuum cleaners are recommended. They should be equipped with a flexible hose and a variety of attachments. For general cleaning, the brush attachment may be used. For the removal of mold the crevice tool is recommended. Vacuums used for cleaning items from the collections should be no more than one to one and a half horsepower.

  • Dehumidifiers

Dehumidifiers may be either permanently installed or portable. The permanent systems will in general be more effective and cost efficient, but more expensive to install. Portable systems are useful in correcting localized problems and in emergency situations. The type of system chosen will depend on the prevailing environmental conditions as established by a monitoring program prior to purchase.

  • Desiccants

Desiccants are useful in humid tropical climates for maintaining microclimates within cases and cabinets. A variety of types and absorbencies are available, from scientific and chemical suppliers. Silica gel is widely used in the United States and Europe. Nikka pellets are more widely available in Asia. Desiccants should not be placed in direct contact with books or papers, but should be contained in trays or fine mesh cloth bags.

  • Air Conditioners

Lowering the temperature at which collections are stored is beneficial in terms of prolonging the life of paper and other book materials, but can cause problems in areas where relative humidity is high. Before air conditioning is installed, conditions must be carefully monitored to insure that relative humidity will not increase to dangerous levels. Local heating and cooling specialists should be consulted in order to determine which available equipment can most successfully modify both temperature and relative humidity.

  • Air Quality

Filtration of air to remove particulate matter can reduce the incidence of mold growth, but cannot eliminate it completely. Local ventilation specialists should be consulted in order to achieve the maximum filtration possible without interfering with air circulation.


The equipment necessary for the removal of mold growth should be acquired and maintained in working order in every institution in the tropics. At least one staff member should be trained and delegated to take charge of any treatment and to supervise other staff members in the event of a moderate or major outbreak.

  • Vacuum Cleaners

Low power hand held or canister vacuums should be used in removing mold from the covers of books. The crevice cleaning tool should be used rather than the brush attachment. The vacuums chosen should have disposable paper collection bags, not reusable cloth bags. See Prevention above.

  • Mini-Vacuums

Mini-vacs are used for the removal of mold from the surface of paper. They are most useful where mold is an infrequent occurrence. Most models may be operated by either direct electric power or with batteries. They are available through camera and electronic equipment suppliers.

  • Vacuum Aspirators

Vacuum aspirators, like the mini-vacs are used for the removal of mold colonies from the surface of both books and paper. They are more effective than the mini-vacs, and are a worthwhile investment where mold is a recurring problem.

Vacuum aspirators are relatively easy to construct, and require:

1. A small vacuum pump with regulator.
2. A 3' length of clear plastic tubing of appropriate inner diameter to fit the vacuum pumps intake port.
3. Two sections of 1/4" inner diameter glass tubing, one approx. 8" long and the other approx. 4" long.
4. A 1000 ml Erlenmeyer flask.
5. A two hole rubber stopper for the mouth of the flask.
6. A 5' length of clear tubing of appropriate inner diameter to fit the glass tubing.
7. An eye dropper with the suction bulb removed.

Clear plastic tubing is preferable, as it can be monitored for the build up of spores on the inner wall of the tubing and changed as necessary. Opaque rubber or plastic tubing may be substituted if clear tubing is not available. If the air intake port and the glass tubing differ in size, tubing of appropriate size may be joined with plastic tube connectors.

The aspirator is assembled by attaching the 3' length of tygon tubing to the air intake valve on the vacuum pump regulator. The other length of the tube is attached to the 4" glass tube and this is inserted into one of the holes in the rubber stopper. The 5' length of tubing is attached to the 8" glass tube, and the tube is inserted into the other hole in the rubber stopper. The stopper is then placed in the mouth of the flask. The large end of the eyedropper is inserted into the unattached end of 5' tubing. The eyedropper and the length of tubing form a tiny vacuum cleaner. The mold is collected in the flask. The mouth of the eyedropper should be smooth, and may be sanded with emery paper if there are any irregularities. When the vacuum pump is plugged in, the pull of the vacuum may be regulated by adjusting the intake valve.

In an emergency, when electrical power may be off for days or weeks, a vacuum aspirator can be improvised using a water tap. A special attachment (called a water-jet pump) is necessary for the tap, and can be obtained from chemical suppliers. A vacuum is created by the flow of water through the faucet, and the pull of the vacuum can be regulated by increasing or decreasing the volume of water. The 3' length of flexible tubing should be attached to the side opening of the water-jet pump and connected to an Erlenmeyer flask as described above. Any local university or high school chemistry department can provide assistance in constructing a vacuum aspirator. They are quite simple to set up and USE, but rather difficult to describe.

  • Magnifiers

The use of a magnifier will aid in the thorough removal of mold growth. A dissecting microscope with a long arm adjustable stand is best, but will not be available to most. libraries. A headband magnifier provides an acceptable level of magnification, and leaves both hands free. Hand held magnifying glasses may be user if no other apparatus is available.

  • Brushes

An assortment of brushes will be needed. Fine pointed artist's watercolor brushes should be used for removing mold growth from the surface of pastels and other fragile media. Wide crusting brushes of rabbit hair should be used for routine cleaning and the removal of pondered art gum eraser. These dusting brushes should not be used in the removal of mold growth.

  • Powdered Art Gum

The use of powdered art gum for the removal of mold growth from fragile paper is recommended. Powdered art gum is available through most art and drafting suppler stores. If it is not available locally in powdered form, art gum erasers can be cut into small squares and reduced to powder in a household blender. Several different grades or sizes can be made, from relatively coarse to very fine. The larger grains should be used first in order to pick up the mycelium from the paper, followed by the finer grain powder to remove remaining spores.

  • Tweezers

Very fine pointed dissecting or surgical tweezers may be used for lifting mold from fragile surfaces and pastels.

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