The Book Doctor Is In: Book Repair Supplies and Materials

book doctorSince Demco has many kinds of repair tapes and liquid adhesives people have asked for more details about the materials we have been using for these repairs. In this post we discuss some of these product variations and why some may work better than others in specific instances.

An important factor to consider when selecting repair tapes and adhesives is their acidity since bringing acidic materials into prolonged contact with paper will accelerate the natural aging process of that paper. Acidity is measured on the pH scale. In case you’re curious, the term pH is an abbreviation for pondus Hydrogeniun which is a measure of the amount of hydrogen in virtually any material.

The pH scale is a series of numbers ranging from 0 (or sometimes -1) to 15. Somewhat counter intuitively, lower numbers indicate a higher level of acidity. The pH of hydrochloric acid is 0, stomach acid is about 2.75, and wine is about 3.5. Things at the other end of the scale are alkaline, or basic. Oven cleaner has a pH of about 13 and commercial chlorine bleach measures around 9. Pure water sits right in the middle at pH7.

Acid is the primary cause of the deterioration of paper over time. Many books printed before the mid-12th century have pages that still look almost new, but as mass production of paper became commonplace, the manufacturing process introduced harmful amounts of acid into the paper. Probably the bulk of books published from the 1920s into the ‘70s or ‘80s show significant yellowing of pages and are becoming increasingly brittle and more delicate. Since then the better quality books have been printed on acid-free paper which should last well as long as acid isn’t introduced into that paper.

Common sense dictates that you’d want to avoid putting stomach acid or oven cleaner on your books, but what about things with less extreme pH levels? Anything that has an acidic pH will introduce acid into materials it comes in contact with. A good example is found in books that have had pockets glued in with an acidic adhesive — a common practice when pockets were in use. Almost invariably, on the reverse side of the page that the pockets are glued to will be discolored due to the acid migrating into the paper.

So what should you use to repair your damaged books to be sure you don’t introduce acid? Anything with a neutral pH or that is slightly alkaline should be safe.

How do you know what the pH of a product is? In the case of liquid adhesives, Demco has been listing the pH in the product information for quite some time. In general, the pH of tapes is more difficult to determine. The information below is the best that I have been able to obtain from manufacturers.

Liquid Adhesives

Demco Norbond
pH 5.5-6.5
About as acidic as cows’ milk. Probably not a concern in the short run.

Demco Neutral Bond
pH 7-7.5
Neutral to slightly alkaline. Perfect for long-term repairs.

Demco Rubber Cream
pH 9.6
A bit more alkaline than baking soda. That is probably not harmful over time.

Demco Bond-Well 
pH 4-5
About as acidic as wine or coffee. Remember those discolored squares under the book pockets? Don’t use this for long-term book repair.

Repair Tapes

3M 845 Clear Book Repair Tape
pH 7
Should not introduce acid into the books.

Demco Fastape Repair Tape and Demco Vinyl-coated Cloth Tape
pH Neutral to slightly acidic
Used to repair book covers rather than pages so a small level of acidity probably won’t matter.

Filmoplast P Paper Mending Tape (Transparent) and P90 Paper Hinge Tape
pH 7-9
Slightly alkaline. This may help neutralize acid in high-acid paper.

Demco Cloth Binding Tape (Cloth hinge tape, single-stitched and double-stitched tape)
pH can vary toward acidic
Normally coated with Norbond or Neutral Bond when installed so any acid will be blocked from reaching the paper.

As always, feel free to use the link below to post any comments or questions and I’ll respond. I may use your input in future posts.

Throughout this series, we’ll be referring to two resources from Demco. The pamphlet Demco Collection Care Guide and the Demco Collection Care DVD are both available to help you through your book repair challenges.


John Ison

John Ison

John Ison retired in 2011 after working with Demco for more than 25 years, most recently as the Director of Library Relations. During that time he conducted over 300 book repair workshops, wrote the Demco Collection Care Guide, and wrote and produced the Demco Collection Care DVD.