How to Manage Sewing Tension When Pressing Leaves Gaps Between Signatures

First distinguish a gap visible with the textblock closed from one that appears as you open a spread between signatures. Record whether it occurs everywhere, at one end, or beside a particular sewing station. These observations give you a more useful starting point than repeatedly pressing the entire book.

Opening changes the relationship between adjacent folds. Steere explains that the folds move with some independence and that an unfinished textblock without linings or adhesive can visibly separate when opened. Sewing, supports, and linings all influence that movement. Therefore, judging tension solely by the appearance of an opened, unfinished spine can lead to unnecessary tightening. Materials and mechanics for book conservation: Part II

Use the following as a diagnostic sequence derived from those structural principles, rather than as a measurement standard. Examine the thread and paper as well as the gap.

Observation	What to investigate next	First action
A visible loose loop accompanies the gap	Slack in that sewing run	Seat the sections together and take up accessible slack progressively
Separation is concentrated at the head or tail	The end connection between signatures	Check that the kettle stitch follows your binding’s sewing pattern
Thread is seated, but the spine remains bulky	Thread thickness and accumulated swell	Compare the materials in a small trial before resewing the whole book
Separation appears chiefly when opening	Movement of the unfinished spine	Assess it alongside the intended lining and finishing method
Tightening puckers the fold	Excess tension or unsuitable hole spacing	Stop tightening and inspect the affected sewing station

Keep adjacent signatures pressed together while drawing the thread snug. Jana Bouc’s journal-binding instructions specifically recommend holding the signatures together and pulling the thread sideways, parallel to the paper surface, rather than upward. This gives you a practical way to seat the stitch without pulling directly against the edge of the hole. Jana’s Journal Binding Steps

For the signature you are currently sewing, use this working sequence:

1. Align it with the sewn stack and hold its fold against the preceding signature.
2. Inspect the thread inside the fold for an unseated loop.
3. Draw through the accessible slack at the current station, keeping the pull close to the paper’s plane.
4. Continue along the sewing path, checking each accessible span before completing the end connection.
5. Release your hold and inspect whether the sections remain aligned without puckering.

This sequence is an application of Bouc’s seating and pulling instructions, not a specified tension test. The useful endpoint is a seated thread and an undistorted fold. Avoid treating the final pull at the end of a signature as a substitute for checking the preceding stitches.

If the suspect span is already locked beneath later sewing, consider undoing back to it. That makes the affected thread accessible for inspection instead of attempting to correct an unidentified problem through the working end.

Check the connection between signatures at both ends. In Brian Sawyer’s tape-sewn binding instructions, kettle stitches connect the adjoining signatures at the head and foot specifically to prevent gaps at those otherwise unstitched contact points. Compare your actual thread path with the pattern you chose, especially where a gap begins. Stitch the Signatures — DIY Bookbinding

A missing connection requires correcting the sewing path; extra pull elsewhere does not supply that connection. Where the path is correct, compare the appearance of the two ends before continuing. Peachey notes that excessive sewing tension can produce a curved textblock that is thinner at the kettle stitches, and stresses the importance of even tension. A Guide to Swell

Make this a checkpoint after each new signature: inspect the head, inspect the tail, then look along the whole spine. It is easier to investigate a change when you know which signature introduced it.

Swell is the added thickness at the spine associated with sewing thread. Peachey identifies thread thickness and hardness, paper characteristics, signature makeup, sewing style, and consolidation as contributing factors. Thick or hard thread can leave considerable bulk even when the sewing is snug. Compression during sewing also affects the result. A Guide to Swell

Once the thread is seated, further tightening is a poor way to investigate material bulk. Instead, make a small comparison using the same paper and sewing pattern. Try a finer thread while keeping the other choices consistent. Look for a combination that seats cleanly and produces a manageable spine without requiring distorted folds.

Also inspect the holes. Sawyer recommends openings only large enough for the needle to pass through. For sewing around tapes, his paired holes are slightly wider than the tape to avoid puckering. Those details help distinguish a tension problem from a preparation problem. Prepare Signatures for Stitching — DIY Bookbinding

Use a short trial textblock to isolate the variable you suspect. Henry Hebert’s sewing-model project held the paper, thread, section count, and folios per section consistent while comparing sewing structures. The models showed different opening behavior as the supports and sewing changed. This demonstrates why a result from one binding structure should not automatically become a rule for another. Sewing Models

For your own comparison, prepare two small stacks with matching paper, folds, hole positions, and signature counts. Choose only one change: the tensioning sequence, thread thickness, or consolidation during sewing. Write down what you changed so that the comparison remains useful.

Inspect both stacks closed, under comparable compression, and opened to similar positions. Note loose loops, fold puckering, alignment, and where separation appears. These are observations to make, not predicted results. If you change several things together, the better-looking sample will tell you less about which adjustment helped.

Resewing is the practical next step when an identified sewing problem remains inaccessible: a missed end connection, trapped slack, or a distorted span you cannot correct locally. Undo to the affected area while keeping the signatures in order, then inspect the paper before sewing through the existing holes again.

If the thread is seated and the remaining separation chiefly occurs on opening, assess the planned finishing stage. In Sawyer’s case-binding method, the aligned textblock is held in a press before the spine receives adhesive and mull. This places spine consolidation within a defined binding sequence. Glue the Spine — DIY Bookbinding

Use the adhesive treatment specified for that structure. Bouc’s journal instructions call for an even spine coating while avoiding adhesive seeping between the signatures and onto page edges. They do not prescribe flooding an open gap. Jana’s Journal Binding Steps

Before committing to glue, identify what you can actually see: a loose stitch to correct, a bulky material combination to reconsider, or opening movement to assess through the intended finishing process. That decision gives each next step a purpose and keeps additional pressure or tension from becoming the default response to every gap.

• A Guide to Swell — Peachey Conservation
• Materials and mechanics for book conservation: Part II. The impact of sewing on spine structure — The Book & Paper Gathering
• Jana’s Journal Binding Steps — Jana Bouc
• Prepare Signatures for Stitching — DIY Bookbinding, Brian Sawyer
• Stitch the Signatures — DIY Bookbinding, Brian Sawyer
• Sewing Models — Work of the Hand, Henry Hebert
• Glue the Spine — DIY Bookbinding, Brian Sawyer