How to Finish Seams With a Zigzag Stitch
A zigzag stitch is the simplest way to stop woven fabric from fraying without a serger. When the stitch wraps over the raw edge it traps the loose threads and keeps the seam allowance tidy through repeated washing.
Materials
- Woven fabric
- All-purpose polyester thread
- Spare thread for test stitches
Tools
- Sewing machine
- Zigzag presser foot
- Fabric scissors
- Seam ripper
Steps
- 01
Test on a scrap first
Thread the machine and sew a few zigzags on a scrap of the same fabric. Set the stitch width to 3 to 4 mm and the length to 2.5 mm as a starting point, then adjust until the stitch wraps the edge cleanly.
- 02
Position the fabric on the edge
Lower the presser foot so the left point of the zigzag falls just off the raw edge of the fabric. About half the stitch should sit on the fabric and half should hang beyond the edge to fully encase the threads.
- 03
Sew at a steady speed
Hold the fabric lightly and let the feed dogs pull it through at a moderate, even pace. Watch the edge rather than the needle so the zigzag stays half on and half off the fabric.
- 04
Handle curves and corners
On outward curves, stitch slowly and pivot the fabric in small increments so the stitch keeps hugging the edge. At inward corners, stop with the needle down, lift the foot, and turn the fabric before continuing.
- 05
Secure the ends
Overlap the start and finish of the zigzag by about 1 cm, or backstitch gently so the threads do not unravel. Trim any loose thread tails flush with the edge.
What the Zigzag Actually Does to a Raw Edge
A zigzag finish is not a seam — it is a binding laid over the raw edge. Each swing of the needle crosses the edge diagonally, and because the needle only enters the fabric on the left half of the swing, the bobbin thread loops over the loose warp and weft ends and pins them under a column of thread. That is exactly why the half-on, half-off position matters: a stitch that lands entirely on the fabric never captures the edge threads, and a stitch that hangs mostly in the air forms arches that collapse the first time the piece is washed.
Stitch length does structural work too. At the 2.5 mm starting length the diagonal bars sit close enough together that a fraying thread has nowhere to escape sideways — the damage stops at the first bar it meets. Lengthen the stitch too far and you get a comb of wide gaps that loose fibres can work through; the edge looks sealed while it is still on the machine and starts shedding in the laundry basket.
The finish sits on the seam allowance, never on the seam line, so it changes nothing about fit or about the seam itself. You can zigzag an edge before you sew the seam, after you sew it, or on a piece that is already assembled — the stitch only guards the raw edge.
Mistakes That Show Up on the Finished Edge
The classic failure is the stitch drifting off the edge, which leaves a row of fuzzy loops hanging in the air — sewers call it eyelashing. It happens when the fabric creeps left under the foot, usually because it is being pulled or because the edge was trimmed unevenly. Check for it by looking at the finished edge from the wrong side: if you can see loops of thread that never touch fabric, that section of the finish is not doing anything.
The opposite mistake is going too short and too tight. A very short zigzag on a loosely woven fabric perforates the edge along a dotted line, and the edge then tears along that line instead of wearing out gradually. If the edge feels stiff, puckered, or crinkled after stitching, lengthen the stitch (toward 3 mm on loose weaves) and stop pulling the fabric — let the feed dogs do the moving and only guide it.
A zigzag finish is also awkward to unpick, because the stitch wraps the edge instead of sitting in a straight line. Work from the right side with the seam ripper: slide it under the diagonal bars and cut every third or fourth one, then pull the loosened thread out by hand. Cutting along the whole row in one pass is what leaves an edge nicked and frayed, which means more work than the mistake you were fixing.
Thread, Needle, and Tension Choices That Change the Result
All-purpose polyester thread is not just the default here, it is the right choice: the finish sits on the most exposed part of the seam allowance, where abrasion happens first. Polyester has a little give, so it flexes with the fabric in the wash instead of snapping, and it resists the rubbing that cotton thread loses to. Match the thread colour to the fabric if you want the finish to disappear into the edge; choose a contrast colour deliberately if you like the visible stitching as a design detail.
The needle matters more than most people expect. Use one suited to the fabric weight, and change it the moment it starts snagging or making a popping sound — a dull needle pushes the weave apart at the edge instead of piercing it, which makes fraying worse rather than better. The bobbin should hold the same all-purpose polyester as the top thread, so both threads behave the same way where they wrap the edge.
Tension shows up fast in a zigzag. If loops of thread sit on top of the fabric instead of being pulled into it, the upper tension is too loose; tighten it in small steps and re-test on the scrap before you touch the real piece. And use the zigzag presser foot — a straight-stitch foot has a narrow slot that the swinging needle will hit, which is a quick way to break a needle and mark the plate.
Two Variations: Three-Step Zigzag and a Folded Edge
If the machine has a three-step zigzag (sometimes sold as a multi-step or stretch zigzag), try it on anything loosely woven or stretchy. Instead of one stitch per side, the needle takes three short stitches on each side before crossing, which spreads the same coverage over a flatter, denser edge. It sits lower against the fabric and is less likely to bunch the weave, so the finished edge looks calmer. Set the length a step longer than you would for a plain zigzag, because each group of three counts as one swing.
For a finish that hides the raw edge altogether, press a narrow fold to the wrong side first and zigzag over the folded edge instead of the cut one. This is the version to reach for when the inside of the piece will be visible — an unlined jacket or a tote bag — because the cut threads are folded out of sight and cannot shed at all. It is slower and adds a little bulk to the seam allowance, so it is not the one to choose on a close-fitting garment.
Skill level decides which way to go. Stay with the plain close-to-the-edge zigzag while stitch position is still new to you, since it forgives a slightly wobbly edge, and move to the folded version once you can keep the stitch half on and half off for a whole seam without stopping to check.
Pressing, Trimming, and Washing So the Finish Lasts
Press the finished seam allowance before you judge it. A quick press sets the stitch into the cloth where the needle perforated it and stops the finished edge from rolling up into a tube, which is what makes a zigzag look untidy on the inside of a garment. Press the allowance to one side, or open, whichever the seam itself calls for.
Trim after stitching, not before. Snip the thread tails flush with the edge as the last step, and take off any whiskers the zigzag missed with sharp fabric scissors rather than the seam ripper — the ripper can catch a diagonal bar and pull the finish open. Cutting the loose ends first just gives the edge more time to shed while you handle the piece.
In the wash, turn the garment inside out so the finished edge rubs against itself instead of against zips, hooks, and buttons. That single habit is what lets the zigzag do its job over repeated washing: the encased threads stay inside the stitch, the polyester holds its shape, and the seam allowance stays flat and tidy for the life of the garment.
Frequently asked questions
- Should I zigzag the raw edges before or after I sew the seam?
- Either works, but the order changes the result. Sewing the seam first and finishing the two edges afterward is easier, because you can press the allowance flat and work along a long, flat strip instead of a loose piece. Finish before construction only on a fabric that frays badly while you handle it — a loose linen or a bouclé — because otherwise the edges will shed across your work surface before the seam is even sewn.
- Can I use a three-step zigzag instead of a plain zigzag?
- Yes, and on loosely woven or stretchy fabric it is often better. A three-step zigzag takes three short stitches on each side before crossing, so it covers the edge more densely without bunching the weave, and the finished edge lies flatter. Set the stitch length about one step longer than your plain-zigzag setting, since each group of three counts as one swing of the needle.
- My zigzag keeps slipping off the raw edge. What is wrong?
- It is nearly always alignment rather than the machine. Check that the left point of the zigzag falls just inside the fabric, with roughly half the stitch hanging off the edge; if the fabric has crept left, the whole swing lands on the cloth and the edge threads are never caught. On curves, slow down and pivot in smaller increments, and re-trim the edge if it has gone uneven — a wavy edge throws the stitch off no matter how carefully you steer.
- Will a zigzag finish survive repeated washing?
- Yes, on woven fabric, which is what this finish is designed for. The stitch encases the raw threads, and because the thread is polyester it flexes with the cloth instead of snapping at the edge where the abrasion happens. Turn the garment inside out before washing so the finished edge is not rubbing against zips or buttons, and it will keep the seam allowance tidy through wash after wash.