Book Repair for BookThinkers

by Craig Stark

15 May 2012

How to Straighten Warped Boards

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By Craig Stark

One of the most commonly encountered condition issues booksellers face is warped boards. Fortunately, it's also one of the easier problems to solve - as long as you can bring a few simple items and some patience to the task.

But let's look at why boards deform in the first place. As an erstwhile furniture designer/builder I can tell you that this happens because the bookbinder has violated the first principle of woodworking: Whatever you do to one side of a board, you must do the same thing or something similar to the other side - or compensate for not doing it.

Example: If you apply a polyurethane finish to one side of a board but the not the other, over time the unfinished side will curve outward, that is, become convex. Why? Because a finish will help seal the wood against moisture, and when moisture is absorbed by the unfinished side, it expands. And when it subsequently dries out it rarely returns to its original shape because some of the wood fibers have been torn. There's much less chance of this happening if both sides are finished or if the unfinished side is supported by some sort of stabilizing (compensating) framework, such as an apron below a table top.

Now, binders boards (also called davey boards) used to make hardcover books aren't wood as such, but they consist of wood fibers and thus behave very much like wood. (And much older books may have boards actually made from wood.) Typically, binders boards are manufactured as single ply, and the best quality boards are also dense. This density helps prevent deformation because the less porous a material is, the less moisture it can absorb. Still, if we do something different to each side, say, glue porous, uncoated cloth to one side of a board and a less porous endpaper to the other - and also expose the fabric directly to the environment while keeping the endpaper closed against itself - small wonder that deformation occurs to some degree, and sometimes to a dramatic degree if the book is exposed to markedly variable humidity over time or if a poor quality binders board has been used. Of course, some board covering materials can also prevent deformation. Calf, for example, is usually less porous than cloth or paper, though vellum absorbs moisture at a much higher rate than calf.

But enough of this. How do to we straighten things out?

I suppose all of us have tried the Harry Handyman approach - pinching the corners of the deformed board, applying pressure with a thumb at mid-point, and bending it in the direction opposite the warp. With practice, it's possible to develop a more refined feel for how far a board can be bent short of creasing or breaking it. The problem with this method is that it places enormous stress on the joint, especially at the extremities, sometimes to the point of causing noticeable damage or even splitting. And there is always the risk of over-bending, no matter how much experience you have - and in any case, the board tends to spring back into the warped state or very nearly so.

So, several things are called for here - a means of stabilizing the joint, a means of uniformly applying bending pressure to the board and safely calibrating the degree of bending ... and time.

Two blocks of wood placed as near as possible to the joint and hinge, respectively, and two spring clamps tighten things up, preventing any bending. A spacer block - I used a section of a foam paint roller to distribute the tension created by the clamps evenly - is then clamped between the fore edge of the board midway between the two corners and another block of wood running parallel to the fore edge. Finally, two C-clamps are placed near the corners and carefully tightened so as to bend the board. It's important to use C-clamps, not spring clamps, on the corners because this allows you to adjust them to any tension. It looks like this:

Once the clamps are in place, let things be for a day or so. If it seems to correct the problem, let the book sit for awhile to make sure it doesn't return to its warped shape. Another clamping may be necessary. And please - try this on a book you can afford to experiment with first.

If the board covering is on the convex side of the board (and the pastedown on the concave side) - it happens occasionally - it's possible that the outer covering material has been stretched and/or separated from the inner board, and restoring it to its original position will produce wrinkling in the cover material. In this case it's probably best to leave well enough alone.

Another possible situation: If both the boards and the spine of the book are warped in the same direction, prop up one end of the book, convex side up, and place a weight - I use my geode for this - on top of it. Be prepared to wait for several days, perhaps a few weeks, before the book returns to normal. And it will!

Questions or comments?
Contact the editor, Craig Stark

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