|This is my preferred method of construction in an elastic waist pant or skirt. The credit for this goes to Sandra Betzina.
1. cut a length of non-roll elastic 4" less than your waist size
2. butt the ends together and place a piece of cotton fabric (or a piece of gross grain ribbon) on the ends and carefully zigzag over the ribbon or fabric catching both ends of the elastic. Do this on the other side also to secure the ends properly.
3. Now in your pants or skirt, serge, zigzag or fold under 1/4" ( I prefer zigzagging to turning under, it eliminates all bulk) and neaten the edge, then place your elastic and fold the fabric over the elastic, sandwiching elastic between two layers of fabric.
4. using a zipper foot or a regular foot, sew through both layers of fabric close to the elastic edge(be careful not to sew over the elastic). Keep stretching and pulling the elastic as you sew. This way you get a very 'snug' casing and there is very little bulk which is impossible to get with the conventional elastic casing method.
Try it and you will never go back to the conventional 'elastic casing' method. I have never gone wrong with this method!