Originally Posted by
juliasb
Unbleached muslin is one of the few things I prewash. I use of great deal of both bleached and unbleached muslin for blocks as well as backing and do not take a risk at unbleached muslin since it is not washed or treated the same way as bleached muslin.
I found out this the hard way, though shrinkage was not the issue. I wanted to use muslin for a quilt back. I normally don't prewash. I do spray baste. Whatever the muslin was treated with it cancelled out the sticking property of the spray baste. I started quilting and the whole back just wasn't stuck on. I thought maybe I didn't spray well so I "unquilted" and sprayed a second time. The same thing happened!! Ended up scrapping that back and using something else. Now, if the fabric I have chosen for the back seems treated or "sized" I wash it first.