Prism99

I have been giving this quilt some thought. If you are willing to take the quilting out, as in option #2, I think there are several things you can do to make this quilt strong. If you decide to take out the quilting, be sure to Google "how to skin a quilt" before you start to get some tips on how to make this job easier and faster.

After looking at your quilt some more, I think that a lot of the issues arise from the use of cotton interlock for the sashing and backing. I used cotton interlock for my daughter's dresses years ago, so I know how soft and stretchy it is. Most people who make t-shirt quilts, whether or not they first use fusible interfacing on the t-shirts, use regular quilting cotton for the sashing. Sewing a stretchy fabric to a non-stretchy fabric will prevent the seam from stretching enough to break the thread, even if you use a straight stitch instead of a small zigzag.

It is not a good idea to try to replace the sashing fabric. However, I am thinking you could replace the backing with a woven quilting cotton. Quilting would do what I described above -- secure a stretchy fabric to a stable fabric, preventing the quilting thread from breaking. I do think you might have to change to a smaller, closer-together quilting pattern (it could still be straight lines) to make sure that only small distances of the interlock seams are exposed to stretching.

Replacing the backing fabric and adding closer quilting would probably be enough. I am not an expert on fusing interfacing to stretchy fabrics, but I am thinking that trying to fuse a single piece of interfacing to your quilt top would be difficult because of all the seams. If you do want to try fusing, definitely make up a test block with your fabrics first, including seams, to make sure it will do what you want. Also, the brand and type of interfacing you use would be very important. The wrong kinds would add considerable weight and stiffness to the quilt. My concern about using a lightweight fusible such as Pellon P44F, which is often used to line tie silk before cutting into shapes for quilts, is that it might not be heavy enough for the cotton interlock. Again, if you want to try this, test the fusible on a scrap of the interlock to make sure it will prevent it from stretching.

It seems to me that changing the backing fabric to a woven cotton would be enough. I would spray baste the quilt sandwich together to ensure the top fabric does not stretch while you are quilting. If you really, really want to line the quilt top, then instead of fusible interfacing, I would look for an extremely lightweight muslin, prewash and dry it for shrinkage, and spray baste that to the underside of the quilt top. Muslin will not dissolve or come apart the way fusible interfacing eventually does, even if the muslin is very fine. You would want to spray-baste these two layers together -- which makes it a temporary fusing. The muslin would be the very cheap kind -- as thin and flimsy as you can find. You do not want a heavy, good quality muslin for this job.

Honestly, though, I don't think you need to line the quilt top if you (1) replace the backing with a woven cotton, and (2) quilt more closely. Maybe make up a test strip to test. If threads still break, then add the fine muslin lining to the top.

Edit: Peckish has a point. What thread did you use for the quilting? In addition to all of the above, I would recommend switching to the heaviest polyester thread that looks good. Polyester thread is stronger than cotton thread, so a polyester thread the same weight and ply as a cotton thread will be less likely to break. Glide is an excellent brand, but Superior Threads has good ones too. I would look for a poly thread with a weight similar to Glide. Bottom Line, for example, would be too fine. Look for a matte finish in the poly thread, if possible. (Glide is slightly shiny, as are many polyester quilting threads.)