The Welt Seam or Folded Seam method is an alternative method of corset construction that involves constructing all layers of a corset at once, panel by panel, from the front busk to the rear lacing. Bones are enclosed in the seam allowance of all the layers, on only one side of each seam. I was never satisfied with calling this method the 'Welt Seam Method' because I don't feel that is precisely accurate, so I dubbed it the 'Folded Seam Method'.
This is my personal favorite method of constructing a corset, and one that I recommend to beginning corsetmakers. The strengths of this method are that it is quick, doesn't require extreme accuracy and precision in sewing, and that it produces a very durable corset. It has its limitations, such as not accommodating double-boned seams, and it may not be the best method for every corset, but I feel it deserves consideration as one of the easiest corset construction methods. I've taught this method to beginners and had great feedback regarding its ease of use.
Before construction begins, there are a few things to note. First, because the bones will be encased in the seam allowances, make sure the seam allowance of your panels is large enough to completely cover your chosen boning. For ¼" (6mm) bones, I find 5/8" (15mm) works fine, generally. I also like to have extra large allowances at the front of the first panel and the rear of the last, to enclose the busk and rear bones. In this case both of those allowances are 1½" (38mm).
The folded seam method can be used with a variety of layers, although it requires at least two fabric layers. I typically use one fashion layer, one strength layer, and one lining layer - but it can also work with two strength layers. The thicker and more numerous the layers, the thicker your seams will be, and at some point your sewing machine will struggle to sew through them. I find this method works particularly well when your lining layer is also a secondary strength layer, like twill or even a second layer of coutil.
My example corset is a commission and the fabrics were chosen by my client. The fashion fabric is a printed thick cotton, strength layer is very sturdy white cotton duck, and the lining she chose was a thin natural muslin. I flat-lined this muslin to another layer of muslin to decrease any pressure points or visible seam allowances on the inside.
1. The first thing you have to do for the folded seam method is to decide which are your top layer(s) and which your bottom. Generally I like to have my fashion fabric and strength layer on top and my lining on the bottom. The only reason it matters is that the seam allowances and waist tape may be visible through fabric that is too thin, so you need to make your decisions about where your thicker layers are needed. All the 'guts' of your corset will be sandwiched in between your top and bottom layers.
I have left the seam allowance off my lining piece for my first panel due to my method of busk installation (below).
2. Install your busk in your front panels. You can use any method you may be used to. In this case, I wanted to avoid the bulk of doubling the duck in the first panel and wanted my busk to be securely covered, without any seams. So I installed the loops via buttonholes in the top layers, wrapping the fashion fabric and duck around the busk, folding the raw edges under, and stitching next to the busk. I installed the knob side in the same fashion. You may insert your waist tape at this point as well.
3. Now we are ready for our first seam. Place your top layer(s) of panel 2 right side to right side on your first panel. Match your waist and any other markings. Pin lightly.
Next you want to also align panel two of your bottom layer(s) or lining in the same way underneath your first assembled panel.
You want to pin through all the layers, keeping everything correctly aligned. This is the most challenging part of this method.
You'll notice in the photos that I have my waist tape stretching off to the right. I cut the tape the approximate length of the waist, leaving it a bit long, and attach it to the first panel. Throughout the corset assembly, it's important to keep the tape aligned at the waist. It will be stitched into each seam as you go and will be in the very middle of your corset layers.
4. Now that all our layers are pinned together, stitch your seam through all layers at once.
You may mark your stitching line or not, whatever you are used to. With a 5/8" (15mm) seam, I typically can use the guides on my machine with decent accuracy. The nice thing about this method that makes it beginner-friendly is that because you are stitching all layers at once, you don't have to worry that slight inaccuracies in stitching will prevent your layers from lining up correctly.
5. Now you fold the top and bottom layers of the corset into place. All the seam allowances of all layers are now in between your top and bottom layers. If you are very concerned about the bulkiness of your seams, you may trim some of the seam allowances now, but I've never found it worth the trouble. I like the strength the added layers give to the bone channel and added structure to the corset.
Press your seams into place, pressing both top and bottom. I then secure my layers with three pins at the edge of the new panel: top, waist, and bottom. I make sure to pin down the waist tape so it doesn't shift or get caught in my stitching. I also am careful to pin the lining correctly because it can easily shift and wrinkle during the next steps, causing problems.
6. Topstitch close to your seam line, within 1/8" (3mm). This is the left side of the bone channel.
7. Stitch a line for the right side of the bone channel the appropriate width away from the first line of stitches. You will find you need to make your channel wider than you might with other methods because of the room all the seam allowances take up. Test your first channel by inserting your chosen boning and adjust your width as necessary. Make sure your stitching IS catching the seam allowances, though, to prevent them bunching up within the channel and causing bulges.
Here is what the interior of the corset looks like. If you have a lot of seam allowance left, you may want to trim it to prevent the edge from showing through.
8. Repeat steps 3-7 for each seam of the corset, on both halves. I typically will do both halves at the same time: panel 1, panel 1, panel 2, panel 2, etc. It's easiest to keep track of the cut panels that way.
For very curvy seams, it may be necessary to cut notches in the seam allowances to get them to lie flat, but I try to cut as few notches as I can get away with because that weakens the bone channel. So I only cut notches on the side seam of an underbust and nowhere else. Obviously this will differ based on pattern.
9. Finally, after stitching all your seams, you reach the rear of the corset. To form the rear seam, we will be folding the seam allowance of the top and bottom layers inwards, pressing, and top stitching. I mentioned that I leave a large seam allowance at the back, and that is to give two layers of strength fabric between which to slip the rear bones. So your seam allowance at the back should be however wide your rear bones and grommets will be (unless you are using two strength layers, in which case the extra seam allowance is not necessary).
Here you can see I have folded and pressed the top layer's seam allowance under, but not the lining yet. (I will cut the waist tape to the appropriate length.)
I press the lining layer so that it is JUST shy of the edge of the top layer, to keep it from being visible from the back. Then I topstitch as close to the edge as I can while still catching the lining. You may want to stitch this seam twice, for security.
10. I then mark and stitch the channels for my two rear flat steels, measuring from the back edge of the corset.
If you wish at this point you can put in your grommets and try your corset on. I waited to grommet until last.
11. Now you have a corset with all the panels together and boning channels at each seam. Now you can decide if your corset needs additional boning. As mentioned earlier, double boning, i.e. having one bone directly on either side of each seam, doesn't work well with this method. Because the seam allowances are all on the far side of each seam, any bone you insert on the near side won't look as thick and will be lopsided in appearance.
I prefer to insert bones into the center of each panel (or in smaller sized corsets, leave just one bone per seam). You can insert bones anywhere you wish either by slipping a tubular bone casing in between the corset layers or by inserting a strip of coutil or other strength fabric. I am using the latter method.
Here is a strip of the same duck I used for my strength layer. I will slide it between my lining layer and the existing duck layer to create a thin two-layer section. Pinning it in place, I mark my stitching lines with chalk and stitch my bone channel.
12. Now all the bones can be inserted into the channels. You can also do this as you go, but I find it faster to cut, tip, and insert all my bones at once at the end. I try to insert all my bones between two layers of strength fabric at the center of the seam. There are many layers of fabric protecting the bones in the seams and there is NO way they are going to work their way through all those layers. (As someone who wears my corsets very frequently, it's one of my favorite things about this method.)
13. And that's essentially it! All that remains is binding the corset and adding grommets and it's done!
It is also possible to use this method and have a floating lining. You can either attach the lining after all the panels are together, OR you can assemble your lining first. If you have your lining panels completely assembled and pressed, you can then attach them to the front when installing the busk.
Then for the rest of the construction, simply keep this layer folded away from your work. Here is an example of that technique:
I still constructed the corset as described above, simply didn't include the lining in my stitching of each seam.
I hope this tutorial has been helpful and clear. I'd love to hear your experiences with this method, whether or not you've ever used it before.