many years ago, tg found a couple of chairs in the garbage. they were great except for not having seats! so i cut out circles of mdf and upholstery foam, covered them with cotton twill, and voila! they looked great, for a little while.
but i learned a few things.
like, cotton twill does not stand up to being left outside in the rain and snow for six or seven years.
and, piping is not just decorative, it's also strengthening. i had just cut a biiiiig circle of the twill, gathered all the extra and stapled it under. so there was no reinforcement of any kind at the "edge" of the foam. and eventually, the fabric wore away. if i'd seamed and piped, first off the fabric on the piping isn't under much strain the way structural fabric is, and secondly, even if it does start to wear through, you just lose a bit of piping, as opposed to having the whole covering fall apart. lesson learned.
this time i did it right: indoor/outdoor fabric, and piping!
being exceptionally slow these days, i bought the fabric about 6 weeks ago, and a week after that got the chair seats measured, and a week after that got the fabric cut, and the week after that got it sewn, and then last friday i finally stapled the new covers on. whew. i have more cushion covers cut out, but they may just wait till next year.
recovering upholstered seats:
you'll need a staple gun for this, and fabric and cording.
first remove the seat from the frame. turn the chair upside down. on my chairs, there were three screws holding each wooden seat base to the metal frame. remove the screws and save for later. now you can work with the seat independent of the chair.
measure the seat. trace the shape onto a piece of paper, measure around the outside, and measure the total depth (foam, wood, everything).
cut out fabric, making sure to add seam allowances - 5/8" on each edge, with an extra 2" for the edge which will be stapled to the wood underneath. also sut a strip of fabric for piping, and cord the same length.
step one: right sides together, sew ends of each long rectangle, making two loops (one for the seat edge piece, one for the piping).
start by making the piping. fold the fabric in half lengthwise wrong sides together, and set the cord into the valley of the fabric, trimming cord to fit if necessary. sew the length of the fabric, as close to the cord as possible.
fit the edge piece around the edge of the seat piece, wrong sides together, sandwiching the piping in between. stagger the seams of the edge piece and the piping, so the fabric doesn't get too bulky. sew through all layers.
turn the seat cover right side out, and pull it over the seat. turn the seat upside down, tug the fabric firmly over the wood at one edge, and staple down. next, rotate the seat 180 degrees, and pull & staple the fabric snugly at the opposite side of the seat. continue in this way around the edge, going back and forth to opposite sides, to make sure the fabric is evenly stretched in all directions. think about it this way: if the first staple went in at 12 o'clock, the next should go in at 6 o'clock. then, you'd do 3 o'clock and 9 o'clock. then 7 and 1, 10 and 4, and so on and so on.
once the fabric is nice and snug, and you've got a staple every 1/2" to 3/4" around the edge, drop the seat back into the frame, and screw in using the screws you removed earlier.