A zipper that is going to be used in a cardigan must be able to separate – an open ended zipper. It’s best to plan knitting so that the front opening will be just the right size for a “standard” zipper length, typically 18″, 22″, 24″, etc. But if you finish the sweater and discover that the opening isn’t quite the same as a standard zipper length, then purchase a zipper slightly shorter than the opening. Sometimes the front edge may be “eased” a little bit into a shorter length zipper…or, the zipper can begin and end half inch from the top and/or bottom of the sweater. When selecting a zipper, if you can’t find an exact color match, go a little bit darker, or go with something neutral, such as black or navy to go with darker colors, etc.
There are also choices of zipper style, such as sport versions having large plastic teeth, or coiled teeth, or metal teeth, etc. These are all a matter of personal preference. Most critical is getting the right length, color, and that it will separate – open ended.
To prepare the zipper for installation use Wash-A-Way Wonder Tape …. It is not necessary, but you will find that it is helpful.
With zipper still zipped, align each cardigan front edge with the zipper tape, taking care to position the front edges of the cardigan where you want them to be. (Sometimes you want the zipper to be seen when it is zipped. Sometimes you want the zipper to be hidden when it is zipped. For the latter case, there will probably be some sort of special treatment on the front edges, such as a folded over placket, or an I-cord knit in, which will form the portion which will cover the zipper.) Many sweaters have the front edges that are made up of garter stitch which is two stitches wide. This particular stitch does not lend itself well to covering over a zipper, so the zipper teeth will be seen when the zipper is closed.
When placing the zipper into position, it is also critical that any horizontal “lines” inherent in the garment match up. For instance, the part where a collar is attached needs to line up, that is, to be in the same position on the right side as it is on the left side. Similarly, the top edges should line up, and the bottom edges should line up when the zipper is closed. (The horizontal white strips shown in this next photo mark the places in which alignment is critical.) This photo shows the zipper taped in place, though I’ve added some stick pins to hold it together, too.
Press down firmly on the taped areas to allow the tape to adhere well. (If the assembly is allowed to sit for a few hours, the tape seems to become a bit tackier and adheres better. However, this also will make it be a bit “gummy”, but for me, it is a small price to pay for the “help” in holding things together better.) Carefully unzip the zipper. I generally add many pins to keep the zipper/garment properly in place.
Any zipper may be sewn in by hand but only certain zipper installations allow for sewing in by machine. If the zipper is going to be hidden by a folded over or I-corded front edge, it will probably work best to sew by hand, since you don’t want the machine stitching to ruin the look of the folded over facing, etc. If the zipper isn’t going to be hidden, and if the front edges of the garment have a bit of texture, such as seed stitch or garter stitch, then if a nice matching thread is selected, the zipper will lend itself well to being sewn in by machine. The stitches may be detected if studied closely, but for the most part, they are very difficult to see. These next photos illustrate this – all of these zippers were sewn in by machine, yet it is extremely difficult to see the lines of stitching.One drawback of machine stitching is that it may be more difficult than hand stitching to remove if any adjustments are required in the zipper installation. A couple of advantages, however, are that machine stitching is quite fast, and also very secure.
Sew a stitching line on each side of the zipper as close to the front edge of the fabric as the garment allows, about 1/8″ away from the edge of the knitting is good. If using a sewing machine, a standard straight stitch (2.5mm) is best, though a longer stitch length (3.0 or 3.5mm) may be better for bulkier knits. If sewing by hand, use a backstitch, being careful to keep stitches from showing on the outside of the garment.
At this point, feel free to cover the inside of the zipper with your choice of trim. I’ve never used any sort of decorative covering over my zippers, because I think that if the zipper tape edges are secured neatly by hemming them in place, it already has a very clean finish…but using a nice trim to hide the inside of the zipper might be fun. Again, make sure to keep the edges of the trim far enough away from the zipper teeth to allow free movement of the slider.
For a sweater with a folded down collar facing, use a matching thread to secure the front edges of the facing to the zipper tape, again making sure the slider moves freely.
Feel free to let me know if any of this is confusing, or if anything is missing, or if you’ve found this information helpful, or if you have a better idea! Have fun!