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3.12 Freezing and Drying Wet Books and Records

The successful recovery of water-damaged library and archival materials depends on timely response to a disaster. Rapid response maximizes recovery of collections materials and expedites the restoration of services. To extend decision-making time regarding salvage and replacement, freezing is the most viable option for most institutions. Because it inhibits mold growth, freezing allows the time to determine if value, use, and format of the original are important, or to de-accession or purchase replacement materials or materials in a different format. Freezing also provides a respite to review insurance policies and vendor contracts. Finally, freezing will allow time to find space for air drying, determine if there is adequate staff and time to air dry, and to handle large incidents in a smaller, more controlled atmosphere.

This leaflet will walk you through the process of freezing books and records, and it will explain how to dry them once retention and funding decisions have been made. For a more general introduction to recovery, see NEDCC Leaflet 3.6 “Emergency Salvage of Wet Books and Records.”

Freezing Books and Records

Before beginning any recovery efforts, the water source must be considered. Rarely is the water clean and free of debris. What is contaminating the water? Is the contamination corrosion from a pipe, dirt and debris from a flood, salt water, or is there sewage involved? If the water is sewage-contaminated, call in a professional recovery service immediately; do not deal with the salvage in-house. If the water is only contaminated by rust, dirt, or salt water, rinsing wet books and records before freezing helps by removing debris that could be difficult to clean off after drying. If sufficient trained labor and time are available for this step, set up three or four bins of clean water. Holding books closed tightly, dip them gently in the water moving each book from bin to bin. This process will expose them to successively cleaner water and remove much of the surface debris. Over time, make the last two bins the first two, replace the dirty water in the first two bins, and move the clean water bins to the final rinse stage. If records are mud-covered, rinse by supporting the records on a piece of plexiglass or other rigid, inert support, and rinse with a gentle stream of water from a hose or pitcher. Do not rinse if the inks are soluble; instead, freeze them immediately, mud and all.

Begin by working with priority items first, if you know what they are. Realize that these materials are going to be fragile, especially if wet, and that they will be larger and heavier than normal. Sort materials by degrees of wetness as you remove them from the shelves. Taking time to do this will make drying much more efficient. Degrees of wetness can be considered with these main categories in mind:

Damp: Cool to the touch, having been exposed to high humidity; can be identified after the event by mold formation.

Slightly wet: Noticeably wet with staining to the textblock, binding, folder, or pages, no more than ½” in from the edges. These areas will have been in immediate contact with water.

Wet: Noticeably wet with staining more than ½” in from the edges up to saturation; can be based on the length of time exposed to water.

When packing materials for freezing, work with sturdy, uniform packing containers. Label each container as to content and the degree of wetness. Loosely wrap books with wax or freezer paper and pack one layer deep, spine down. Pack books of similar size in a box to prevent distortion.

When packing records, leave documents in their boxes and folders if possible. If boxes are damaged, pack folders into containers laid on their sides for ease of filling. Interleave with wax or freezer paper every couple of folders.

Pack oversize materials of similar size and wetness between flattened cardboard boxes and wrap with tape. There is no need to interleave with wax or freezer paper unless the items are printed on coated paper or have colors that could bleed. Move packed items to a freezer immediately.

Ideally, your disaster plan identifies local freezer space that is available in the event of an emergency. If there are no such spaces in your area, it is possible to rent a freezer truck or portable walk-in freezer. Make sure whatever you rent is of sufficient size and can maintain temperatures at or below 0° F to prevent the thawing and re-freezing that exacerbates distortion in paper-based materials. When filling the truck, do not over-pack. Spreading materials out as much as possible will speed the freezing process.

Because freeze drying will cause more harm than water for some commonly held non-book materials, the following materials should NOT be frozen:

  • Audio and video tapes – Air dry or keep wet until sent to a professional recovery company
  • Computer tapes, disks, compact discs, or CD ROMs – Rinse if water was dirty; air dry
  • Ambrotypes, daguerreotypes, or tintypes – Air dry

Drying Frozen Materials

Materials can remain in the freezer indefinitely and will eventually dry there. If drying in the freezer, expect items to be inaccessible for several weeks to many months, depending upon the temperature of the freezer and the degree of wetness. However, the goal should be to return these materials to circulation as quickly as possible to maintain service continuity. There are two primary options for drying frozen materials: air drying and vacuum freeze drying.

Vacuum Freeze Drying

Vacuum freeze drying is best suited for large numbers of wet books and records as well as for materials with water-sensitive inks and coated paper. Frozen books and records are placed in a vacuum chamber. A vacuum is pulled and a source of heat introduced while the overall temperature remains below 32° F. The materials are dried by a process called sublimation: the water in the solid phase (ice) is removed from the materials in the gaseous phase without passing through the liquid phase. Thus there is no additional wetting to cause distortion beyond that incurred before the materials were frozen. If materials have been stabilized quickly after becoming wet, very little extra shelf or storage space will be required when they are dry.

Although this method may initially appear to be more expensive because of the equipment required, the results are often so satisfactory that additional funds for rebinding are not necessary. In addition, mud, dirt, and/or soot are lifted to the surface, making cleaning less time-consuming. If only a few books are dried, vacuum freeze drying can be expensive. However, companies that offer this service are often willing to dry one client's small group of books with another client's larger group, reducing the per-book cost and making the process affordable. When dealing with commercial vendors for drying, communicate clearly from the beginning about costs, handling, and expectations.

Air Drying

Air drying is the most common in-house method of dealing with water-damaged books and records. Because it requires no special equipment, it is often believed to be an inexpensive method of drying. However, air drying is labor intensive, diverts many hours of staff time to regularly monitor the process, and often results in a distorted finished product. It is not an option for books with coated paper. The rehabilitation costs after air drying tend to be greater than other methods because most bound materials require some form of treatment from pressing to full rebinding; documents often need flattening and rehousing.

Due to the time required for air drying, it is not unusual for mold to develop during large-scale operations.

In addition to mold growth and coated papers blocking, another consequence of air drying is the extra amount of shelf space required for collections. Depending upon how long materials spend in the freezer and the length of time spent air-drying, the amount of additional shelf space required after drying can be 20% or more.

How to Air Dry Frozen Records

Air drying is most suitable for small numbers of records, so work with small batches from the freezer at a time. Records with water-sensitive media should be left in the freezer as long as possible or vacuum freeze dried.

  1. Identify a clean, dry, secure space where controlled temperature and humidity are available. Reduce the relative humidity as low as you can to prevent mold growth and improve drying conditions.
  2. Set up the space: Cover tables, non-carpeted floors, or other flat surfaces with unprinted newsprint, blotting paper, or paper towels, and hang clothesline.
  3. Keep the air moving at all times using fans in the drying area. This will accelerate the drying process and discourage mold growth. Aim fans into the air rather than directly at drying records.
  4. Thaw out small groups of records at a time. A small group will be one that you have the space for or time/staff to deal with from beginning to end. Depending on how long the items were in the freezer, the top and bottom pages may already be dry and separated.
  5. Carefully separate the frozen records as they thaw. If the paper is stable or strong, you can carefully peel the pages as they thaw and lay them out on your prepared surface or hang them up to dry. If the paper is fragile, you can put a support sheet of Hollytex or Reemay (an open-weave spun polyester fabric) on the top document and carefully peel the single item back. Move the single document on its support to the drying space and lay face down. Take the support sheet back to remove the next document. If you encounter any resistance as you are separating a leaf, stop. Resistance indicates that the paper is still frozen and damage will occur if you continue.
  6. If work on a group of items cannot be finished in time, the items can go back in the freezer until time is available.
  7. Once completely dry, records may be rehoused in clean folders and boxes, or they may be photocopied or reformatted in other ways. Dried records will always occupy more space than ones that have never been water damaged.

How to Air Dry Frozen Books

Note: Books containing coated paper should be vacuum freeze dried and not air dried after freezing.

  1. Identify a clean, dry, secure space where controlled temperature and humidity are available. Reduce the relative humidity as low as you can to prevent mold growth and improve drying conditions.
  2. Set up the space: Cover tables, non-carpeted floors, or other flat surfaces with unprinted newsprint, blotting paper, or paper towels, and hang clothesline.
  3. Keep the air moving at all times using fans in the drying area. This will accelerate the drying process and discourage mold growth. Aim fans away from the drying books.
  4. Start thawing out small groups of books. A small group will be one that you have the space for or time/staff to deal with from beginning to end.
  5. Stand books on end with boards fanned open in a space with good air circulation, but – again – do not aim fans directly on the books. As the text block continues to thaw, fan open pages. Turn books head to tail daily.
  6. To minimize distortion of the edges, place volumes in a press or press under a board with a weight just before drying is complete. Paper- or cloth-covered bricks work well for weights.
  7. Wet books should be left frozen longest before air drying or vacuum freeze dried. As the books thaw, assess the degree of wetness remaining. If the books are slightly wet or damp, proceed as in step 4. If the books are still wet, as the books thaw, interleave every 16 pages or so with paper towels or clean, unprinted newsprint. Be careful to avoid interleaving too much or the spine will become concave and the volume distorted. Complete the interleaving by placing clean blotter paper inside the front and back covers. Close the book gently and place it on several sheets of absorbent paper. Change the interleaving frequently. Turn the book from front to back each time it is interleaved. Once the book is only damp, proceed as in step 4.
  8. Frozen pamphlets should be thawed and removed from any pamphlet binders if possible. If the pamphlet opens well, open it to the center fold and carefully hang it from clothesline. If the pamphlet is thick or opens poorly, dry it on a flat surface as above. Flatten when dry.
  9. Dampness will persist for some time inside the book in the gutter, along the spine, and in the boards. Due to their thickness, boards retain moisture much longer than fanned out leaves in the text block. Mold is often found between the boards and flyleaves in books that are not dried completely. Check for mold growth frequently while books are drying.
  10. When books are dry but still cool to the touch, they should be closed, laid flat on a table or other flat surface, gently formed into their original shape, and placed in a press or held in place with a board and weight. A piece of Melinex or blotter paper should be put between the boards and the text block to prevent moisture wicking into the text block from the wetter boards. Press overnight and set up to dry during the day. Continue this cycle of air drying and pressing until books are dry. Do not return books to the shelves until they are thoroughly dry; otherwise mold may develop, particularly along the gutter margin.
  11. If you can establish an air-conditioned room capable of maintaining a constant relative humidity of 25 to 35% and temperature between 50 and 65°F, books with only wet edges can be dried successfully in approximately one week once fully thawed. A wet book may take up to two weeks to dry so it is best to leave in the freezer as long as possible before thawing and drying. As stated earlier, exceptions are books printed on coated paper and those with water-sensitive media.


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