Leave it to the Longarmer 

by Lyn Crump
Are you a topper?  A person that likes to make quilt tops, but not the wrestling of them through the small space on your domestic machine needed to quilt them. You prefer to leave it to the longarmer to quilt.  Then this article is for you plus every other patchworker.
The backing fabric you use on the back of a quilt can make a large difference to your finished quilt top.  You have most probably cursed the fact that your longarmer wants you to have 8 inches more fabric on both the length and width of your quilt top.  I know that is one fifth of a metre and on a double bed quilt it is the equivalent to at least another metre of fabric. There are multiple reasons for this request.
Most cotton fabrics will shrink up to 5%, on a large backing fabric this can be up to 5”.  If you wash and iron your fabric for your backing before sending it to your longarmer you may be surprised to find it is now much smaller. If you don’t iron your backing, your longarmer will still want to get the wrinkles out.  They may lightly spray it with water and yes it will shrink.
Backing fabrics are attached to the poles of longarm machines by pins, zippers or grips.  Usually with a selvedge edge along the pole as this is a straight edge. All of these methods require about 2 inches of backing fabric on both the top and the bottom of the quilt.  So that the needle plate of their machine does not hit the pins etc another two inches of grace is required.  There goes your extra 8 inches so I hope it hasn’t shrunk too much.
The 8 inches at the side of the top – do you make sure the backing fabric is completely square?  Is the grain of the fabric true to the selvedge? Has it been cut or torn from the bolt?  If you have a large flat surface that you could lay your backing fabric on then you might see that the straight of grain actually moves quite a few inches away from that cut edge.  Longarmers use the extra fabric at the sides to keep your quilt top square to your backing fabric.  Most longarmers will clamp the sides of the backing fabric so that pleats are not formed in the backing. It also gives them a small space to check their threads and tension on your fabric with your wadding.
If you are going to use normal width fabrics for your backing then there are some things you can do to piece your backings to achieve better results.  You will still need to have the extra fabric in the length and width of your backing!  All seams in backing fabrics need to have the selvedge removed from them.  They need to be stitched with a smaller length stitch, a  ½” seam and backstitched at the ends.  The seam then needs to be pressed open.
If your top is going to be quilted with a pantograph then the seam in your backing will need to go across the quilt, so that it runs parallel to the rollers of a long arm frame.  If you have the seam so it runs vertically down the quilt there will be a build up of fabric in one place on the roller and the sides of the backing fabric may be loose.
If you are going to piece your whole quilt backing, make sure that the seams lines of your backing are not close to where the seam lines of your top are. Make sure the grain lines of your different backing pieces are the same.  Lay it out on the floor and make sure it is laying  flat. It is not possible for a longarmer to guarantee that they get the centre both vertically and horizontally on a pieced top and back.  The process of quilting itself will shrink a top depending on the density of the quilting.
Consider the colour of your backing fabric.  Most longarmers will use a similar coloured thread in the bobbin as they do on the top of a quilt.  So a similar coloured backing fabric to the thread you would prefer on the top is preferable.  If you are going to want your longarmer to be changing coloured threads and doing more custom type quilting then a busy printed fabric is better choice for your backing.