180 pages of 120gsm, sewn on three tapes. It opens to about 90 degrees and then the text block springs shut, and if I push it flat there's an audible crack from the middle of the spine. Straight PVA on the spine, dried under weight overnight. Did I glue it too rigid or is this a sewing problem?
Did you round and back the spine? A flat-back block of 180 pages sewn on tapes is always stiffer than it looks. Rounding gives the sections somewhere to go when the book opens, and backing creates the shoulder the boards hinge against. Without it you get exactly the 90 degree wall you're describing.
I didn't. I'd assumed that was decorative. Adding it to the next one.
Also look at how much glue went on. Thin coat, worked into the folds with a stiff brush, then wiped back. You want it between the sections, not sitting on top as a layer. A thick bead across the spine is a hinge that can only break.
You can partly rescue this one. Open it in stages from the outside in: front board, back board, then twenty pages at a time front and back, pressing the gutter gently with the flat of your hand. It won't undo the grain problem but it'll stop the cracking getting worse.
@coptic_cleo · 2mo ago · 3 replies
Two things and they compound.
Grain direction first. For a book that opens flat, the grain of every sheet, the endpapers, the spine lining and the boards has to run head to tail, parallel to the spine. If your text paper runs the wrong way the block fights you forever and no glue technique fixes it.
Second, straight PVA dries into a hard plastic shell. A spine wants flexibility, so either cut the PVA with about 25-30% wheat or methyl cellulose paste, or buy one sold specifically as flexible bookbinding grade. The crack you're hearing is that glue film failing, not the sewing.
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@abd_avery · 2mo ago
Tore a test sheet both ways and my grain runs across the spine. Well, that explains the entire first book.
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@margot_teller · 2mo ago
The tear test is good, the wet test is more definitive if you're unsure. Cut two 2cm strips at right angles, wet them both, the one that curls more across its width is running the other way.
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