When you cut sashing strips, remember that you'll lose a total of 1/2" from their width after sewing strips to the quilt blocks.
Once you've decided how wide sashing strips should be, determining their length is simple -- cut strips that equal the unfinished measurement of the quilt block. If your blocks are square, all of your strips will be the same length. If you're making rectangular quilt blocks, you'll need strips for each dimension.
Take care when making your quilt blocks, pressing as you go to ensure that blocks are the correct unfinished size. Even if they differ slightly, cut strips to equal the length the unfinished block should be. My patterns all tell you how wide and tall a block should be after it is assembled, but if your pattern does not, add 1/2" to the finished width and height of a block to determine its unfinished size.
What About Cornerstone Size?
Cornerstones have sides that match the width of your sashing. For instance, if you cut sashing strips that are 3-1/2" wide, your cornerstone squares (or patchwork cornerstone units) should measure 3-1/2" x 3-1/2".
How Many Sashing Strips & Cornerstones Are Needed?
Make a sketch of the quilt's layout -- nothing elaborate, all you need is a quick look at the basic design. Refer to the drawing above and ask yourself:
- How many blocks will be sewn across in each row?
- How many rows will the quilt have?
- Do I want sashing on the outer perimeter of the quilt, as shown above, or will I reserve that space for a first border?
Sketch-in the sashing strips and cornerstones and count them -- the elements that you'll sew between blocks in each row and strips and cornerstones that will be used to create the narrow rows that separate blocks. Read a few yardage calculation basics if you're not sure how much fabric you'll need.
Assemble the Quilt, Sashing & Cornerstones
- Sew sashing units vertically between each quilt block in a row, and to the ends of rows if you've chosen that look. Press seam allowances towards the sashing strips. Repeat to assemble all rows with quilt blocks.
Be sure to carefully align the ends of sashing strips to the ends of each block they're being sewn to. If the lengths match exactly, that's excellent. If they do not, fold the sashing strip crosswise to determine its midpoint. Determine the block's midpoint, too. Match midpoints and ends carefully before sewing to help square-up the block.
- Sew cornerstones and sashing together to create the narrow rows that are placed between rows of blocks. Begin and end with a cornerstone unless you are not sewing sashing around the outer perimeter of the quilt. Press seam allowances towards the sashing. Repeat to assemble all narrow rows.
- Sew all rows together, matching seam intersections carefully. Press the quilt.