The inside of the drawstring waist band was badly deteriorated. But the rest of the pants was in perfect shape. So, I was asked to do something to make it better again.
The first step is to remove all the worn part of the waist band. (This is the part that takes a long time because I have to do this by hand with a seam ripper.)
Then, I prepare a new waist band to attach to the pants and just sew it on!
This process is the fast part. And it's all done.
Sometimes people ask me why it takes a long time to "just cut off the bad parts and sew in a good part". If I simply cut off the bad part, then, the seam allowance will be cut off as well, and the fit of the pants will be different. So, in order to preserve the same shape, I have to take the original seams out and sew on a new waist band where the old one was. My contractor friend always tells me that the most important part is the preparation. This so applies to sewing as well. It takes time to prepare well to come up with a good result.