When first learning about the effects of grain the focus is on the negatives of not having the grain run head to tail in a book. But there are times when paper grain can be used to advantage. The issues come about because when paste (moisture) is applied to paper the fibre in the paper expands in width not length. So, when you paste out a piece of paper it expands or stretches perpendicular to the grain. Once the paper is adhered to a board and dries it contracts applying a strain to the board. If this strain is from head to tail the board will buckle head to tail and tear the joint between the boards and the text block. But this strain can also be used to advantage. Some people in a recent class noticed that after covering the boards curled out towards the fore-edge. But once the text is cased in the drying pastedown will counteract this and pull the board back in towards the text.
Last week I had a problem while doing a springback binding. The way I’d constructed the tabs had resulted in them curling out. Since they have to be inserted into split boards, I wanted them flat. So, I pasted bank paper on the tab to pull them back in straight. When doing this you want the paper to expand as much as possible. So, paste out the paper with wet paste and leave it for awhile and then paste again. The result was nice flat tabs.
An interesting side note. While researching springback bindings I found a number of authors suggest that for the piece of thin board or card used to make the tab it is one of the few cases when it might be advantageous to have the grain run spine to fore-edge. The reason being that the leaver will be cut out of the tab and needs to be as stiff as possible because it will be used to open the spring.
DAS Bookbinding 