Moisture in close conjunction with books is one of the most common ways to lose your collection. Even if you are able to salvage the books and dry them out, they will always show the effects of the environment. When you store them in a place with high humidity, or if a storm or leaking water pipes causes the problem, there are some steps you can take to protect your books from moisture.
There are several steps you can take to provide protection for your book collection, even when the books are subject to high moisture levels. These include choosing the right location, controlling humidity, and keeping the air moving.
From a preservation standpoint, both humidity by itself and humidity combined with temperature extremes are challenges for book lovers in all sorts of environments. If you are looking for some solutions which are affordable and can be easily accomplished, read on.
What causes book damage from moisture?
The fibers which comprise the pages in your books and the covers are largely made of trees and wood pulp from recycled paper, cardboard, and similar products. These fibers are made of lignin and cellulose, plus some glues which hold the fibers together.
The covers of the books may be manufactured from thick cardboard or card stock, sometimes covered with a fabric of cotton, linen, or even man-made materials. The covers of high end books can be made of leather. The pages of the books are created from paper with varying levels of chemical bleaching and treatments. When more bleaching is applied, the paper is a whiter color. Some grades of paper will be more likely to absorb moisture than others.
Because of the different levels of treatment to arrive at the final paper or boards, different absorption rates are found when comparing pages and covers. The result is rippling of the pages, and often bowing of the boards which form the covers of the books. It is likely that page edges of the books that have been exposed to moisture show stains or ‘high water marks’.
Other types of damage which are caused by dampness include fading of dyes from the covers onto the pages. The type face may also be affected by moisture on the pages. Glues used in affixing the paste downs and the binding at the spine may be more or less water soluble. In worst instances, books may literally fall apart and become a sodden mass of paper pulp.
As a secondary problem when books become moist, mold spores may take up residence on the covers and on the page edges. Mold and mildew are destructive to the paper, and can quickly infest an entire collection of books. For all these reasons, it is important to identify problems with moisture in an area where books are stored, and to take steps to correct the issues.
TIP: More information about book storage conditions is available at ‘How Do You Store Books In Your Basement’.
What is too humid for books?
The humidity of your book storage area can vary significantly, depending upon the ambient conditions outside and inside the building. When there are elements in the building and in the book storage area that add to the moisture in the air, the relative humidity goes up, while when the surroundings are drier, the relative humidity is lower. You may think that keeping the books as dry as possible is the best solution, but air that is too dry can cause damage to books as well.
Humidity in your book storage area is also limited by the temperature of the surrounding air. The common belief is that warm air holds more water than cold air, but this is an oversimplification. The fact is that water molecules in warm air hold more energy and are more difficult to condense, while water molecules in cool air condense more easily. When humid warm air contacts a cool surface, the loss of energy causes rapid condensation.
When your books are stored in an area with high relative humidity, your books become a breeding ground for insects, mold, mildew and formation of acid spots known as foxing. Mold will quickly take hold when the air temperature and even slight moisture are present. Mold not only grows quickly, but the spores can ‘jump’ from one book to the next quickly, infecting your entire library. When mold is detected, the book(s) involved should be moved into isolation and treated.
So, there is a recommended level of moisture in the air and the temperature of the air. Cooler temperatures and lower relative humidity are preferred to high temperatures and higher relative humidity. Book restorers and archivists suggest that a good balance between temperature and relative humidity is 68°F to 72°F and 45% to 55%, respectively. These are the same levels that humans would find acceptable.
Cooler temperatures are not damaging to books; in fact some books are frozen as part of a treatment for insect infestations.However when low temperatures are combined with low humidity, it can cause the paper to dry out and become brittle, while low temperatures and high humidity cause condensation. High heat and very low humidity can also result in brittleness and damage to the glue in bindings, especially.
When discussing the best humidity levels for books, it is important to keep in mind that rapid fluctuations in the humidity/temperature balance in either direction can be as much or more of a problem to the condition of your books as temperatures and humidity somewhat above or below the ideal. This caution is particularly important when there are dramatic changes in the temperatures in the surroundings.
An ice storm with resulting power outages can affect the condition of your books. Similarly, a heat wave when the air conditioning system is struggling to keep up may cause the books to warm up too rapidly and they may be affected by the heat/humidity combination.
How do I protect my books from moisture damage?
Moisture damage is the result of high humidity, causing the paper pulp to swell unevenly. The way to protect against such damage lies in storing books correctly. There are several elements which affect storage. These include location, temperature/humidity, air flow, and cleaning.
Book storage places often are wherever the owner can find room to put a bookcase. Bookcases or books packed in storage containers should not be placed against an exterior wall. Temperature/humidity levels tend to vary too much there. Books should not be placed in damp basements or musty attics, because of temperature and humidity variations, as well as the prevalence of insects and pests. Books should not be placed in an area where they are exposed to ultraviolet rays of the sun, which damage the composition of dyes and paper.
For those who live in a smart home, a device which automatically adjusts the temperature and moisture levels of the area where books are housed can help to avoid sudden fluctuations. Dehumidifiers are another device which can be linked to operate automatically so that the humidity levels do not change dramatically.
Avoid placing books in cardboard boxes, particularly if the boxes are stored in an area that might be subject to flooding, dampness, other elements that put moisture into the environment, or pest predations. Some examples include placing live plants near the books, an aquarium with aquatic plants and fishes, near a laundry facility, on a covered porch, and near a pool or water feature.
Temperature and humidity
Keep the temperature in a range between 68 and 70 degrees, or even somewhat cooler, but changes in the temperature should not be sudden, but rather spread over several days. The recommended humidity level is 45 to 55 percent, but some archivists recommend a relative humidity of as low as 35 percent. The appropriate temperature and humidity levels have the effect of warding off insect attacks, which is not directly linked to moisture damage, but is a secondary cause.
Mold and Mildew
Regular cleaning of your books and bookcases is one of the best ways to avoid a proliferation of mold and mildew blooms. These fungi rely on moisture and dust mites, as well as other organisms to provide food to utilize in growing. Mold is not only harmful to your book collection directly, but can cause health problems with anyone who comes in contact with harmful spores.
Insects and other pests
Insects look for moisture, food supply, and appropriate temperatures for their nesting locations. They can feed on the pages, glues, and bindings of the books, without leaving the book. Making the surroundings less comfortable for the pests may help to prevent damage.
Moisture in association with your book collection, directly or indirectly, is one of the most frequent problems for book owners. Keeping the humidity levels at the appropriate levels through mechanical or digital means is important to maintain the best condition of your books.