In both our Tis the Season and Urban Country Quilts books, we discuss this exact topic. You will see the very same topic in our book Tis the Autumn Season that releases in June 2013 as well. And in each book we say basically the same thing, only in a different manner in each one!
So.....do we prewash? Or don't we?
drumroll please.......and the answer is........
That's right we don't prewash our fabrics. (as i look over my shoulder looking to see if the quilt police are on their way......)
We all have a lot of laundry to do already so why add to the load? Pardon the pun!
The fabric that is being manufactured in this day and age doesn't have the shrink rate it did even 20 years ago. The dye is much more stable, so unless you are using a hand dyed fabric, this shouldn't be an issue. (Having said that, let a quilt sit somewhere soaking wet and you will almost always have trouble!)
The sizing that is in the fabric cut directly off the bolt makes for a crisp hand and are definitely easier to work with this way.
In todays fabric market, we have access to all varieties of precuts, 5" squares, 10" squares, 2-1/2" strips, and much more. These items are not meant to be pre-washed, to do so is asking for trouble! These items will simply fray too much to be manageable. And besides, who wants to iron those little bitty squares into submission?
The other thing you most certainly do not want to do is prewash a finished quilt top. That is a recipe for disaster. You will end up with frayed seams, threads hanging everywhere, and depending on the type of fabric, maybe some very frayed edges. And you most certainly will have to iron it before you could even think about basting and quilting it.
We don't prewash our quilt batting, or our backing fabric. If you really feel the need to wash the quilt top, be sure to do it after the quilt is put together, quilted and bound. This way, all the fabrics will do whatever shrinking they might do (minimal!) and you will end up with a beautiful quilt with an overall scrunchiness that says....use me!