The Importance Of Interfacing When Sewing Facings
A faced finish is used when a clean, structured, stitch-less edge finish is desired. A facing is a separate compartment taht is cut at the exact shape of the garment area housing the faced edge. In order for the faced edge to remain properly structured and stable in the finished garment application, interfacing is used to back either the garment layer or the wrong side of the facing strip. Additionally, the interfacing allows the finished faced edges to remain stable enough to house the facing compartment, and result in a flat and more structured finished edge.
While your pattern set my not include separate patterns for the interfacing, you can use the facing patterns to cut the individual interfacing pieces. Make sure to cut the pieces such that each fusible surface corresponds to the wrong side of the garment edge it backs. Treating the interfacing's fusible side as the right side and cutting the patterns in the same way as the actual facing pieces will ensure the fusible interfacing is cut in the correct alignment.
To minimize bulk and thickness within the finished face edges, it is best for interfacing no t extend into the seam allowance. For that reason, you should trim the seam allowance off all interfacing pieces.
The resulting interfacing layers should then be aligned within the seamlines, not extending into the seam allowance area. Conventionally, interfacing is fused to the wrong side of the garment. However, if your facing is the one requiring more stabilizing or the garment design/fabric doe snot work well with interfacing, you can fuse the interfacing to the wrong side of the facing layers instead. The best example in this case is when the garment's edge to be faced features gathers or pleating, or it drapes out into a flowey shape that could be compromised by the added structure. In this case, the facing layer backing these edges should be interfaced instead.
If the faced edge houses a garment closure such as a zipper, the interfacing should stop at the seamline and not extend into seam allowance layers housing the closure.