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There are a lot of ways to sew a facing in a garment with an invisible zipper.
I will share my way of finishing a facing with an invisible zipper this be used for any facing, like a faced neckline, skirt or pants waistline. I always add a small flat button and fabric loop at the top to reduce the stress of the zipper. (the fabric loop is made of bias cut lining and steam pressed into a small flat loop shape)
Cut the facing the same length as the waistband including the seam allowance.
Sew the facing at the waistband but leave the first 3 inches (7,5 cm) from the zipper on both sides free, these will be sewn later.
If you want to add a button and fabric loop, sew the fabric loop at the zipper tape about 1 cm below where the zipper pull if the zipper is zipped up. For this example for a skirt I sewed it at the left side.
The facing seam allowance at the top should be moved/angled about 1 cm away from the seam allowance of the zipper.
The lower part of the facing matches the seam allowance.
Sew the facing at the zipper tape
If you plan to line the garment, do not sew the last ½ inch (1,5 cm) from the facing, so you can insert the lining at the facing bottom later.
Push the zipper coil flat and fold the zipper towards the facing part.
Stitch the remaining facing at the waistline but do not back stitch.
Turn the facings to the inside, and check if the stitching line of the facing is even.
If the facing is even on both sides turn the facing again towards the inside and back stitch , grade the seam allowances and cut the corners at an angle.
Finish the faced zipper by sewing on a flat button.