to wash first or not
 

I purchased backing for my king sized quilt in a 108" x 4.5 yd. piece of muslin. I dread having to iron this large piece of muslin if I wash it first. Any problems with too much shrinkage if I don't wash it first?

I understand your dread of that ironing chore. However, in my experience there are many grades of muslin and some shrink a lot!! I would much rather get the shrinking done before I invested all the time in quilting it. Too much of a risk for me. But I do prefer less shrinking/crinkling in my finished quilts than more.

Wash it... mine shrank close to 9 inches.... rather before than after.

I bought legacy muslin from joann. Nice quality. 90 inches length shrank to 85 inches in length. This muslin did not shrink in width.

I had "pre- shrunk" roc- lon shrink a lot when i washed it. I do not remember the exact numbers now.

I measure most of my fabrics befor and after washing.

I would wash it for sure. Adjust it a couple times while drying and take it out promptly to minimize wrinkles.

Oh yes!!! Wash it first! Muslin shrinks a lot. I prewash everything. I don't want any surprises with the end product.

i agree. i once did a test on a 3 yard piece of yardage and it shrank almost 4 inches in one direction and more than 1 inch in the other

I would suggest you wash it. Muslin especially shrinks and you don't want to be disappointed if you don't wash it and put it on the back of your quilt which I am sure you put alot of time and effort into and have it shrink up. Good Luck.

All fabrics shrink. I washed 3 pieces of backing fabric to get the sizing out. They were so stiff. Each shrank 5" crosswise and 1" lengthwise.
That's a lot of shrinking even if you want a crinkly look.

I prewash 99% of my fabric, including all my backing - and never had to iron any of it. I put a large 100% cotton towel in the dryer, dry on mid-low heat and take out as soon as it's dry, which isn't all that long.

I find with backing, ones it's washed it relaxes and is more straight of grain. Some of it gets quite stretched out of shape when folded at the factory.