​How To Sew A Self-Finished Zipper Underlay

A self finished technique is the simplest way to sew a conventional zipper underlay. This underlay style is constructed from a single fabric layer that is self-finished by folding onto itself to enclose its raw edges.

1. Measure and mark the rectangular fabric strip directly on the wrong side of the fabric. This rectangular fabric strip should be at 1" longer than the zipper length and double the width of the final underlay. Since the underlay should entirely cover the zipper, it should be about 2-3" in with, thus the initial fabric strip in this case is 6" wide. 

Carefully cut along the marked lines. 

2. Fold the fabric strip lengthwise with face sides touching and all edges aligning. Insert pins through the bottom horizontal wedge corresponding to the underlay's bottom edge. 

3. Stitch the horizontal bottom edge at 1/4" seam allowance. Flip the underlay on its right side and iron the clean-finished bottom edge fo r smooth flat finish.  

4. Clean finish the underlay's vertical raw edges  using the technique of your choice. In this case a serging stitch is used to encase more edges together. Similarly, you can use a zigzag stitch available on your home sewing machine. 

5. Place the underlay on the wrong side of the zipper application such that it covers the entire zipper length. Align the underlay's vertical clean-finished edge with the zipper's seam allowance (or facing edge as shown above). Insert pins horizontally through both layers to secure. It may help to move the garment layers completely out of the way in the process so you can comfortably pin only through the seam allowance layer. 

6. Machine stitch the pinned edge together halfway down the seam allowance as shown. 

7. Tack the underlay's  bottom open corner to the opposite seam allowance or facing edge using a hand-applied whipstitch as pictured above. This stitch should only be appleid through the layers on the zipper's wrong side and not visible on the garment's face side.