Adding blocks to backing question
 

I am thinking of adding a column of 9 in. square blocks to yardage.
The quilt top is 49 in. wide, yardage is 43 in. wide.
Can I get by with a 1/4 seam vs 1/2 seam?
If my math is correct, the semi finished backing = 51.5 in.
quilt top =49.0 in.
The column would be on the side of yardage.

Thanks for your help!!
Jo Anne B.

I don't use a wider seam allowance when piecing backing, so I think you're fine there. I only use a wider seam allowance for rag quilts, or when the fabric weave is very loose. I assume you're cutting the selvage off the backing.

The problem is that when you quilt, it is very hard to keep the top and backing exactly straight together. This means that when you trim the quilt, you will probably be cutting off some of your blocks that are on the back. Also, it's better to make the back more than 2.5" bigger than the top. Would it be possible to put another strip of fabric next to the line of blocks, so that the top is wider? It could be a different fabric, if you're out of the one that is 43" wide.

The idea behind the 1/2" seams on the back is that you press the seams open rather than to one side. The purpose is to reduce bulk & make it easier to quilt. Generally, the back does not have foundation quilting like the front so those seams do not get any extra reinforcement from the quilting. As a result, the only thing holding together a seam that's pressed open is the stitching itself. If you don't have enough fabric to do 1/2" seams, I'd definitely shorten your stitch length to between 1.4 - 1.6mm (16-18 stitches per inch) so it has that added reinforcement and would probably backstitch the beginning & end of any seams that won't be enclosed when you start quilting. Also, I'd strongly recommend using a cotton thread in that case as it will swell and shrink closer to the same rate as your cotton fabric when washed, reducing the rubbing & stress on the seams.

EDIT: You can also get a tiny bit more mileage out of the WOF by leaving part or all of the selvedge edge on. I do this all the time & it works out quite nicely.

I do have enough yardage to add a strip, my concern is the alignments(?) (the fabric is directional) will come out wonky.
I have the option not to add the blocks and just piece the yardage.
I can make the blocks a column or a row. Here's a pic of the backing.[ATTACH=CONFIG]551354[/ATTACH] The design is bigger than a quarter, smaller than a 50 cent piece.

My thought is: if adding blocks it will break up, a less noticeable probable off center direction of the print when pieced together.
Or... the original hope of adding a column of blocks and avoiding directional wonkiness.

If you have enough, I would definitely make it finish more than 2.5" beyond the quilt top ... but that's me. I like to have 2-3" on each side to quilt on my DSM so what I'd do if quantity of fabric isn't an issue would be to find a place on the flower print where I could match them up nicely & then just cut the excess seam allowance down to 1/2". In theory, sewing the two selvedges together should match up perfectly, but I know it doesn't always work out that way in reality. Having just the one seam would certainly be the easiest option for quilting. I did that for a similarly arranged backing fabric with matryoshka nesting dolls by Robert Kaufman. The backing came out perfectly straight & you couldn't see the seam unless you were within a couple inches of the quilt and were looking for it.

The other option I'd consider if I really wanted those 9" blocks on the back (they sound lovely) would be to add a 2-3" finished strip between the 9" blocks & the print fabric to give you a bit more backing to play with. I'd seam them in with a 1/2" seam and press open.

I would add a column wider than 9" inches. Maybe two strips running either side of the blocks. If you make it off center, there is less of a need to make it straight.

It will be tight but it will work since I have done this before. I piece the backing the same as a top with 1/4" seam.

If I sew large pieces of fabrics together to make a back I usually use 3/4 - 1" seam and press them open.
They do not cause a problem when quilting.

Think I will concede, keep it simple and add the blocks as a row even though it speaks to me as a column.
I have 3 yds(108 in) of the backing fabric, cut at the 54 in. add the row of blocks and then add more yardage.
This quilt was one of my first, and I am replacing the backing, maybe best to get it right the second time.
Thanks everyone for your input!! JB