In this tutorial, I am going to show you how to replace the elastic in a swimsuit with a self-tie waist bottom.
There are some specific things you need to do compared to a regular leg bottom.
Here are the step-by-step written instructions on how to do it. If you prefer to watch the video tutorial, scroll down to the bottom of this page.
What you are going to need for changing the elastic in swimwear
When sewing with swim fabric, make sure you use an appropriate knit needle and possibly a knit foot or even better a walking foot to make it easier on yourself.
In this tutorial, I am going to show how to sew elastic in swimwear on a regular sewing machine with the universal foot. You are going to need only a piece of elastic.
In industrial sewing, it’s very common to use rubber elastic in swimwear. The reason is that rubber elastic doesn’t hold up to water that much. But at the same time it’s not very resistant to the water and salt exposure and gets destroyed in a relatively short period of time.
That’s why I like to use cotton elastic. It’s knitted and the structure it has makes it much more durable and resistant. It will hold on better over time than rubber elastic.
For this project, I’m going to use ¼ inch or (7 mm) wide knit elastic as this is the width used by the manufacturer. I’ll link to the type of elastic I use in the description below.
I have a rule to be as consistent as possible with the original materials and order of technical steps. This usually gives the best results in repairments and alterations, although there are exceptions.
In this case, the width of the elastic is appropriate for the seam allowance, so I’m going to keep it consistent.
Prepare the bathing suit - remove the ties
Here I have my daughter’s 2 piece swimsuit from last year that still fits. But the elastic has gone completely stretched and the bottom piece is moving around as she wears it.
Surprisingly, the top's elastic is in shape so I am not going to mess with it at this point. The reason for that might be that there is a binding over the elastic, but in any case the elastic is still functioning and that’s why I’m going to work only on the bottom.
What’s specific about this bottom is that it has 4 ties on the sides and the legs are not in a continuous circular shape (image 1).
If the legs are in a circular shape, you may check my other video on how to attach the elastic on waistbands. It might help you get a perspective on how to join the ends of the elastic and how to size the elastic to accomodate for the circular shape of the leg.
There are 4 ties at the sides, 2 at the front and 2 at the back. I need to remove them first in order to be able to start working on the legs and waist from the beginning.
To do that, I am going to look for the openings, left for turning the ties out (image 2). Sometimes these openings are topstitched closed. Very often on swimwear, they are left unclosed as the swim fabric doesn’t unravel. And this is our case as well.
To remove the tie, I m going to turn it inside out and get to the seam (image 3). Then, I’m going to unpick the seam and the tie will fall off.
It’s a serger seam and I have a video on how to easily remove serger stitches.
This tie is off now and I’m going to continue with the other three (image 4).
Unpick the zig-zag top stitching
Now that the ties are out of the way, I am going to start unpicking the zig zag topstitching (image 5). Honestly, for me this is the most unpleasant part. I do have some tricks on unpicking serger and coverstitch seams, but I’m helpless with the zig zag. So if you know any tricks for it, please share in the comments.
Remove the old elastic on legs and waist
As you can see, pieces of the rubber elastic started to fall off (image 6). It’s so damaged that it falls in small, rigid pieces. Sometimes, the rubber elastic gets melted inside of the swimsuit and it’s hard to remove. In all cases, you need to fully remove all pieces of old rubber elastic so it doesn’t stay in the way and make it hard to attach the new one.
You can see now why I prefer the knitted elastic as it can also get stretched over time, but never to this degree and after such a short period of time.
Once I am done with the topstitching, I am going to remove the serger seams that hold the elastic on all 4 sides of this bottom (image 6).
Once the elastic is removed all around, I am going to replace it with the new one.
Sewing the new elastic on legs and waist of the swim suit
In most cases, I would use a serger to attach the elastic. I would also use a walking foot or at least a knit foot to make it easier to feed the slippery swim fabric through the sewing machine. But in this video, for demonstration purposes I am going use only my very basic regular sewing machine with the regular foot.
Fix the lining to the fasion fabric
This bottom has the front lined (image 7). The lining can be on the whole bottom, partually on the front or all over the front as it’s here. In any case, you might want to stitch the lining to the fashion fabric first so that they act like one fabric before you attach the elastic.
I’m going to use a wide zig zag stitch and sew at the edge of both fabrics. This will serve as a basting stitch, although you won’t need to remove it at the end. Just make sure you sew close to the edge so that this seam is not visible on the face side later when you start topstitching the elastic (image 8).
Measure the amount of elastic you are going to need
The next step is to measure how much elastic I am going to need for every section. If this was a new swimsuit, the length of the elastic is usually given in the sewing instructions. But since this is not the case, we have to figure out the length of the elastic ourselves.
The elastic needs to be shorter than the section I am going to attach it to and that’s how it’s going to create some gathering. A bit of the gathering will disappear later with the topstitching as it stretches the elastic.