Bookbinding Materials & Moisture: How to Prevent Board Warping

This video will explore how materials commonly used in bookbinding react to moisture and the resulting forces exerted on these materials, when they've been joined using wet adhesives. The materials most affected are paper, card, board, and leather.

And to a lesser extent, cloth. The main properties and processes will look at a grain stretch and pull. A common problem people encounter when starting with bookbinding is boards warping.

The misunderstanding is that this is caused by not pressing the book hard enough and that the solution is to get a book press - or maybe a bigger, stronger book press. To produce nice flat covers on your book, you need to understand the materials you're working with and how they

interact with moisture. The goal is to balance the forces, the pull on each side of the board, so it doesn't warp. Grain is a property of materials made with cellulose fiber, such as paper, card, and board.

Cellulose fibers are long and thin and in paper, they are bonded together with hydrogen bonds. And in machine-made products these long fibers are aligned in a direction known as the grain direction. If you don't know what the grain of paper is, you might like to watch the grain direction video.

When the material and thus the fibers get wet, the fibers swell in width, but not length. And that leads to the two processes of stretch and pull. So we've got a piece of machine-made paper and we've just pasted it out with wet starch-based adhesive.

The paper absorbs the water into the cellulose fiber that the paper is made of. And these fibers swell in width, but not length. The result is the paper expands perpendicular to the grain direction, but not in the parallel to the grain direction.

Initially, the side of the paper that the adhesive is applied to expands. And of course, the dry side doesn't. This causes the paper to curl away from the adhesive.

Once the moisture permeates through the paper, both sides will have expanded by the same amount. And the paper flattens back out. The expansion of the paper is usually described by bookbinders as a stretch.

Paper that has been moistened or pasted and has reached an equilibrium - not curled up - is said to be relaxed. Now we lay the wet pasted out paper on a piece of board and carefully rub it down, through some rubbing down paper, so that the materials are well attached.

The paper will dry through evaporation and the board absorbing some of the moisture. And eventually everything will reach an equilibrium we will call dry.

But the fibers in the paper have lost the additional moisture and want to return to their original thickness. The paper wants to shrink down to its original width, but is now attached to a rigid piece of board. The board will try and resist the paper's want to shrink, and the mechanical forces of the rigid board and the

shrinking paper will reach a balance which will result in a warped board. Paper warping a board as the adhesive dries is called pull. So this all sounds like a nightmare.

How can you end up with flat boards? The solution is to balance the forces on each side of the board. To do this, you need to understand the characteristics of the materials used to cover the boards.

Let's say we cover the front of the boards with a paper that stretches a lot. But the paper that we want to use for the paste down on the inside of the boards doesn't stretch as much. One way of dealing with this is to put a draw sheet under the paste down, where a draw sheet is a paper with a similar

pull to the front paper. The draw sheet will make up for the lack of pull by the paste down. Maybe the paste down stretches a lot and you're going to cover the outside with cloth.

Cloth doesn't stretch a lot like paper, but it does resist pull well. So even if it doesn't have a strong outward pull, it will resist the inward pull, reducing the warping. I mentioned that the pull due to the drawing paste down needs to be considered in the book construction.

Another consideration with the paste down is the stretch after it is pasted out. Initially, the paste down will curl, making casing in a slight challenge with cased books. A bit of patience and letting the paste down relax and flatten out is a good solution for this.

However, now the paste down is wider than the text block due to the stretch. It is desirable that when the book is closed, the paste down is not visible as extending past the edge of the text. This can usually be remedied after the paste downs have dried, by carefully cutting through the paste down at the

width of the text, being careful not to cut through the turn ins, and peeling off the thin strip of excess paper. Or, the paste downs can be trimmed by the expected amount of stretch before pasting out, which is my preferred method. A scrap piece of paste down paper can be pasted and used to estimate the expected amount of stretch.

You can control pull by using different types of paper. If you want a lot of pull, then use a paper that will stretch a lot. A thin, strong absorbent paper such as bank layout is often used as a draw sheet.

Also thin craft paper. But if you want to minimize pull a coated or heavily-sized hard paper and thicker paper usually stretch less. However, a paper that stretches less may still have strong mechanical strength and may overpower a weaker paper, even

though it's stretched more. Testing and knowing your materials is key. Card and board react a bit differently to paper.

In paper, the moisture quickly equalizes out across the thickness, and the paper relaxes. The curl goes away, but it's stretched. The card and board are usually too thick to relax like paper, but the side that is exposed to moisture will expand

and the board will warp. It will go back to its original shape after moisture evaporates, just as paper shrinks back to its original size. Bookbinders have a couple of rules of thumb for laminating paper and board.

The thinner material should receive the adhesive, and the thinner material should be nearer the text block. So when laminating board and paper, the paper is pasted out and presented to the board. And that side will face the text block.

Another example would be laminating two boards of different thicknesses. The thinner board would receive the adhesive, and the side with the thinner board would face the text block. But as Julius Sumner Miller would say, why is it so?

Let's go back to the board and paper example and imagine we are using thin bank layout paper. If we pasted out the board and put the paper on it, the paper would absorb the moisture from the adhesive, and because it's bank layout, would stretch significantly.

But it's already attached to a board and is restricted in how it can stretch. And the result will be wrinkles in the paper. The immediate impulse is to try and smooth the wrinkles out, which just sets the wrinkles permanently.

This is what gives us the first rule of thumb. Another rule is that the boards should hug the book, not gape open. A slight inward warp on the boards is desirable so that in changing environmental conditions, the worst that occurs

isn't the boards end up flat. No one likes a book with the boards warped outwards. The best way to ensure this is to have the pulling material closest to the text block, and the material that will pull

the most is thin material. Thus the second rule of thumb. But rules are meant to be broken.

You just need to be smart about breaking them. If you do plan to apply the adhesive to the thicker material, make sure the thinner material is the type that will not stretch much, and minimize the amount of water introduced maybe by using a drier adhesive such as PVA.

While we're talking about breaking rules, I'll mention that I do not believe in, or use, the technique of laminating boards cross grain to produce rigidity like in plywood. The only case I have grain running spine to fore edge is in making the lever of springbacks, which is a very specific

and unusual case. Cloth is different to paper, obviously. Bookbinders talk about cloth having a grain, but it's not to do with the alignment of cellulose fiber, but rather the

type of weave and thread twist, the details of which we never really know. The reaction of thread to water and the subsequent action of the cloth is complex, depending on so many factors. It is easier to accept that bookcloth just reacts in some generalized ways and to test, if unsure.

Bookcloth will stretch more - in the traditional use of the term stretch of pulling on the material - in the weft direction than the warp direction. So we say that the grain is in the direction of the warp threads, which is into the roll.

If you have some of the selvedge on the cloth, the grain is parallel to the selvedge, and sometimes fabric will shrink when wet rather than stretch in the warp direction and slightly expand in the weft direction. But luckily, the material that stops adhesive striking through the bookcloth prevents a lot of moisture getting to

the thread of the bookcloth, and these effects are small. Leather is also very different to paper. It also expands when wet.

The direction of expansion is not as predictable. The biggest effect is the leather being stretched slightly when being applied to the book. A small amount of pull is used to set the leather firmly on the spine.

This can stretch the leather from the spine to the fore edge. You try and minimize this, but you do need to get the leather well-adhered to the spine. When the leather dries, it will try and pull the boards outwards.

Leather can apply a very strong pulling force and require significant counter pull to keep the boards flat. I often hear people say that handmade paper does not have a grain direction because the vat man shakes them all in all directions after scooping up the pulp.

I think it is better to think of handmade paper as having two grain directions, and the vat man seldom shapes the same amount in each direction. So one of the grains is stronger than the other.

The issue is that handmade paper stretches in both directions and usually not the same amount in each. This brings all sorts of trickiness to the table. If you are using a beautiful Nepalese handmade paper for endpapers, everyone expects the paste down to stretch from

machine made paper, and you can either trim it before pasting down or maybe after - easy enough to do. But how do you deal with a paste down that stretches in both directions? How do you avoid wrinkles at the fold where the dry and wet paper meet?

There are ways that can get ugly. But I hear you say "My press does make a difference." I've focused on the chemical bonding of the cellulose fibers in paper and board. But these materials have mechanical properties, too.

I guess this is what we consider with stretch and pull. It is possible to permanently deform the paper or board through compression or extension. The material has some elasticity and will bounce back to some extent, but changes in the mechanical properties can be

made permanent. An example of this is drying laminated boards, designed to counter the pull of leather, in a press. Hopefully the boards will resist the same amount of pull by the leather. But you don't have to work with heavily warped board during

lacing in and covering. Flattening boards in a press can be a tricky business. They can respond slowly during and after pressing.

A board that seems flat for a few days may start to warp over weeks or even during changes of season. So where does this leave us on covering boards? As mentioned, the ideal final state of boards is for them just slightly curl in, to hug the book.

This final state is achieved through the design process of making the book. Bookbinders learn the most by binding books, not reading books or watching YouTube videos. The first stage of learning bookbinding is to copy someone, and this is where the books, workshops, and videos come in.

In this stage, you learn the techniques and about materials. Then, based on this knowledge, you start to make design choices such as how do I keep my boards flat while using the desired materials in this book.

Finally, I'd like to suggest a way to deal with pull by simply avoiding gluing out the board paper altogether. Instead, drum it on. Drumming is to attach a material by only gluing the turn ins or at the very perimeter of the material.

From the narrow glued strip of paper, there is insufficient pull to bother the boards. This technique has been used on and off in the history of the book and is now popular with sewn board bindings. I hope this has helped you understand what happens when you laminate materials together with wet adhesive.

I've tried to keep it simple, but provide sufficient detail that you will be able to make design decisions when planning your own bookbinding projects. I should also mention that the terminology I've used - stretch, pull, and draw sheets - is the terminology that I

was taught and has a strong English trade influence. This terminology is not uniform across the English language bookbinding world, but I hope you can translate it into the equivalent of where you are.

Thanks for making it to the end of this very wordy video. I hope you've got something useful out of it. And as always, I really appreciate you hitting the big thumbs up button.

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