The vertical border material can be as thick as you like, 1-2" of finished material is standard, be sure to add 1/2" for seam allowance. For example, for a 2" border, cut a strip of fabric that is 2 1/2" wide. Cut the strip as long as possible.
Sew the t-shirt squares to the long strip of fabric, 1/4" from the edge, right-sides together. Stitch the strip to the right-hand sides of each square, as shown, excluding the squares that will be on the ends of each rows. The t-shirt squares positioned at the ends of each row don't need the in-between fabric because they will be up against the larger, border fabric we will be adding later.
Next, we can turn the squares into rows...
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