I have a quilt on my bed that's over 10 years old. It has many types of blocks so there's many pieces to it. I made it before I knew anything about thread and I am sure bought thread at Joann's. Because I have dogs, it gets washed and dried about 6 times per year. I used to use quilt soap bought at LQS but now I just use Tide. It still has all the stitching intact except for one appliqué that needs a little repair.

Is this the thread you are referring to?
http://www.quiltingboard.com/main-f1...e-t238138.html

If so, I don't think deterioration of the thread is the culprit. The thread would have to already be deteriorated before being sewn (dry rot) to account for this kind of breakage. It's good to keep in mind that the farther apart quilting lines are, the more stress will be put on the thread when the quilt is used or washed. Also, it's a good idea when using a top loading washer to never actually let the machine agitate the quilt. Rule-of-thumb is to stop the washer, agitate by hand (pushing down on the quilt), then advance to spin for both wash and rinse cycles.

If you think about it, hanging a quilt on a clothesline puts tremendous stress on the quilting lines; water is very heavy, and the added water weight in the quilt can cause thread to snap. The same thing can happen in a top-loading washing machine with the typical central post agitator. Thinking back to when I washed clothes in a top-loader, there were many times when the clothes came out all twisted (and sometimes knotted together). This wasn't so much of a problem with small loads (and may not affect smaller quilts, such as those for kids) because they had space to slosh around in the water. A large quilt stuffed into a top-loading machine could get twisted enough to put tremendous stress on quilting lines, especially if the quilting lines are far apart. (The further apart the quilting lines, the more stress on each quilting line.)

I believed in the "break" test for thread too, until I went today and tried out threads I have successfully used in quilts that have been washed and dried. Both the Signature and Glide threads broke easily when I jerked my hands. I think a bigger factor is how close together the quilting lines are and, of course, whether machine agitation in a top-loader was used.

There is a reason why some thread is twice the price of other thread.

A while back last summer actually, I got some thread at an estate sale. $.50 for a bag and took what they had. I had my DH tug on it. It is some sturdy thread and we've both used it. He learned real quick how to wind the bobbin and has patched a couple of his "grunge" shirts. He goes into the bag every once in a while and will not use anyother thread. When he's done he attaches the bobbin to the spool like I showed him with the rubber band. If it passes his tug/snap, it's good to go.

I made my early quilts with Coats and Clark and they have survived decades of washing. I would not worry.

For me, it is now a matter of what my machine likes and the ONLY thread she balks at is Coats and Clark. I buy Connecting Threads thread and like it - even if it is a bit linty. The key is more in the construction than the thread. As long as you use quality thread (not something that's been in grandma's basement for 40 years) you will be fine.

If the thread breaks after the quilting is done tells me that the stitches were too small. Lengthening the stitch length (I generally use 3 mm) allows the thread to work through all 3 layers.

Another possibility - the stitching lines were tight - and broke when more tension was put on them.