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Seam allowance in my quilt blocks comes undone

I have sewn my quilt blocks squares together and the squares are pulling apart because I didn't lock in my stitches.

I tried to do a zigzag stitch over them but my bobbin keeps bunching up.

How can I reinforce my squares?


This has got to be frustrating for you! One of the best things about quilting (unlike all the other things you have to do around the house like laundry and dishes) is that once you finish a block it stays DONE. So let's see if we can't help you find a solution.

It is rarely necessary to reinforce, back-stitch or backtack to secure your seam allowances in your quilt blocks.

Check your Tension

Before anything else, I suggest you check your sewing machine tension settings. A balanced stitch is pucker free with the needle and bobbin threads joining in the middle of the seam. No needle thread shows on the bottom; no bobbin thread shows on the top. it is possible that your needle tension may be too loose.

Shorten Your Stitch Length

After your tension is balanced, next check your stitch length.

You want a stitch that is small enough to hold the piecing together and yet long enough to easily rip out with a seam ripper.

So I use a 2.0 stitch length setting—about 10-12 stitches per inch— for traditional piecing. (Honestly, I'd go down to a 1.75, but my machine is calibrated in .5 increments.) This should be adequate for almost all your piecing needs.

The exception is paper piecing, when stitch length is lowered to 1.0 to 1.5 stitches per inch. This shorter stitch length helps to perforate the paper more closely and facilitate removing the paper.

Back-stitching—generally a No-No

I do not recommend back-stitching to secure the ends of your patchwork blocks or units for the following reasons:
  • It adds bulk.If you back-stitch back into the block to secure the seam allowance, you've added two extra strands of thread. Now multiply that by 2 for the simplest of piecing, like a four patch block. If it's a pinwheel, multiply is by 8. Even with a nice quality 50 wt cotton thread, that adds a lot of extra fiber right where you're trying to match seams.

  • It wastes time without any real added benefit. Most seams don't need back-stitching to secure them. Adding the subsequent unit will cross this seam and secure it. That leaves you with either securing all seams (wastes a lot of extra time) or securing some and not others (adds unnecessary bulk and you're constantly having to decide which seams to backtack.)

If you backtack by back-stitching once you hit the edge of the block, then you'll either spend more time clipping threads...the thread tails aren't at the edge of the block or unit, but in from the edge...or adding another short line of stitches back to the edge of the block. Again, that's a lot of extra fiber in the seam allowance.

There's always an exception... every rule, even, perhaps especially, in quilting.

Do you take your quilts to be quilted on a long arm quilting machine? If so, check with your long arm quilter. She/he may want you to back-stitch on seams that run clear to the outside edge of the quilt.

Racking the quilt top onto the machine puts extra stress on those seam allowances. Back-stitching helps to keep them from pulling apart.

For the long arm quilter, once the quilt is racked, there's no way to go back and re-stitch those seams unless it's done by hand...NOT!

You may want to do this for your own quilts. Again, keep the back-stitching to those outside seam allowances only, to reduce bulk.

I hope this information is helpful in your quest for seams that stay stitched.

Readers, if you have more suggestions, we welcome them! Just use the 'comments' link below to add yours.


Julie Baird

Comments for Seam allowance in my quilt blocks comes undone

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Back stitch or lock seams for quilts
by: Anonymous

I recently made a disappearing 9 patch (which you must cut through the seams). To my dismay, some of the blocks came apart when I washed the quilt. I have a good machine with good stitches so I was terribly disappointed. I'm planning to make another similar type quilt.

What to do?

Julie replies...

Not knowing anything else, I would suggest shortening your stitch length. Also use a 3-ply 50 wt cotton thread for piecing like Aurifil (this is my regular piecing thread.)

I use a 1.6mm stitch length (you can read more about stitch length here which is about 16 stitches per inch.

I am concerned, though, that you said it came apart when you washed it.

Regularly in quilting the seam that crosses a previous seam is what secures it—we rarely backstitch in quilting. That does make me wonder if you possibly ended up with a particularly old spool of thread.

I wish I could be of more help. I am perplexed, too.


Reinforcing seams each end
by: Jackie

Thank you for your post, I am a novice quilter and have been reinforcing my seams each end for fear of them coming undone, I want to make a 'disappearing nine patch' for a child and in this pattern you have to cut through the centres, so obviously you cannot reinforce here, so I was wondering about making it, then I saw you made your stitches much smaller (I was using 2.2)so will try that, I feel much better about making this quilt now.

Thank you from down under.

Thank-you SOOO much!
by: Nicholas

I am working on my second quilt without back stitching any of my block seams and I was talking with a tailor friend who said that i should be back stitching every time, no questions asked.

I said there was no need because every seam edge gets sewn over again when piecing the block but he insisted that my quilts will fall apart. But after reading your comment I feel incredibly reassured about my work!!!

Thanks again, from a novice quilter!

From the Editor: You're welcome! I come from a sewing background and a long line of professional seamstresses. When sewing garments I would always back stitch at the beginning and ending of a seam. It makes sense. Garments are frequently tried on to check the fit during the construction process. You don't want those seams to split. But a quilt doesn't get 'tried' on. The only place that I'd do any back stitching is at the very outside edges. Those are the only places on the quilt where stitching lines don't cross as you are basting your quilt sandwich.

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