How bad is it to mix prewashed and not washed cotton fabric?
 

I am the lucky recipient of several tote bags full of prewashed fabric. I don't usually prewash my fabric. If I'm making wall hangings the fabric may never get washed at all. I'm reluctant to wash some of my precuts. so it is a big no no to mix prewashed and unwashed fabric in a quilt?

I do it all the time with great results. When done I wash with color catchers.

I also do it all the time. Once the quilt is quilted you can't tell. Color catchers are a good idea. I usually prewash darks, but not my whites and light neutrals if I am feeling lazy.

I prefer to wash everything washable before cutting it.

That said, the sun will probably rise and set no matter what we do or do not do.

I DON'T! If project gets washed, the crosswise grain almost always shrinks a bit. (Newly arrived fabric visits the washer at my house before the sewing room.)

I wash before I do anything, but that is because the chemicals on the new fabric destroys my fingernails. But people on here report all the time they use both - washed and unwashed together. If you are going to do a tight quilting one it you shouldn't have any trouble.

Pretty much every quilt I've made ( hundreds) has contained prewashed and unwashed cotton fabrics. I've never had a bad thing happen because of it. Generally I prewash if I'm using deeply saturated colors of hand dyes or batiks that might bleed, if a fabric smells funky or feels funky or if the weave seems kind of loose & I want to tighten it up. If none of those issues are present I don't bother. I always wash and dry my finished projects. I consider it the final step after binding

Initially I prewashed everything. Now I usually just do flannels as they can have such different rates of shrinkage from one piece to the next. So most of my quilts have both prewashed and not prewashed in them. I'm not aware of any major problems as a result.
Where my problems occur are due to either failure to square up before stitching to next section or scant 1/4" getting too scant for whatever reason.

Mixing washed and unwashed fabrics may result in different shrinkage rates, creating different looks between the fabrics. Even wall hangings get dusty and need cleaned once in a while. ;)

Thanks ladies, This was very helpful. I've decided I'm not going to worry about whether a fabric is prewashed or not.