Now to continue...
7) Sewing and Stapling
All your hard work laying out fabric, thinking about which direction the motif should run, and planning how the seams will meet pays off when you begin sewing the pattern pieces together. I began by sewing the decking to the lip fabric, an odd rectangle piece of chevron that has mitered corners. Decking fabric is usually not the same as your pattern fabric but of a similar weight, so choose wisely. Once I joined the grey decking fabric to the lip, I returned to my chair frame to staple them in place. Staple the bottom of the lip to the front bottom of the chair, starting in the center and evenly distributing your fabric over the batting to the right and left, a little bit at a time. Staples should be a couple inches apart–not super close, but not really far apart. When stapling fabric, don't stretch it too tightly, or it will weaken and possibly tear. Finesse it, be gentle but firm. The fabric will go where you tell it to, but don't be harsh with it.
After stapling the fabric to the bottom of the lip, pull the top of the decking fabric underneath the chair back and staple to the chair base, starting at the middle and working your way to either side. Next reach the sides of decking fabric underneath arms and staple them to sides of the chair base. You may need to cut slits near the base of chair arms so that the fabric stays smooth and doesn't fold awkwardly. Use a curved needle and upholstery thread to anchor the decking to the springs below, near where decking fabric is sewn to patterned fabric.
Now it's time to sew the welting. Join 1 1/2 inch wide strips to one another to form one really long strip of fabric the same way you would make bias tape (but ignoring all the double-folding). Then wrap the strip of fabric evenly around cording, place under cording foot on the sewing machine, and sew in place. The cording foot on the industrial machine is so dreamy to use.
To make the arm covers for the Chevron Chair, I placed the welting on top of the center top strip of arm fabric with all the raw edges facing the same direction, then pinned it in place. After pinning, I basted the welting in place to keep it from moving around during sewing. If you omit basting, you MUST remove each needle before it goes under the sewing machine foot. I have broken way too many sewing machine needles by not doing this. Basting the welting in place is really the best method, looks the most tailored, and is how all the couturiers make garments of old. Sew welting to arm top fabric, then sandwich the welting in between the right side of the next piece of arm fabric to be attached, pin and baste; then sew from the side you haven't sewn on yet (this ensures the welting will be evenly placed between layers). Fit arm fabric over chair arms, remembering to smooth the batting. Staple inside arm fabric on top of where you placed the sides of the decking fabric. Before I stapled the outside arms in place, I made sure to place dust cover fabric over the outside arms in order to have a surface on which to place outside arm batting. Staple both in place, fluff batting, then cover with outside arm fabric.
I used cardboard tacking strip to give a nice, sharp edge to the welting and arm fabric that reaches down the side of the chair frame past where the arm ends. Sneak cardboard tacking strip underneath the arm fabric, and carefully staple in place. Staple outside arm fabric underneath chair frame at the sides. Lastly, staple the back of the arm covers to the back of the chair frame.
8) Reuse Old or Cut New Foam
For several decades now foam has replaced traditional stuffing like horsehair in making chairs cushy to sit on. I'm really not a fan of petroleum based products (one of the many reasons I hate polyester), but it's increasingly unavoidable. You can purchase soy foam, but it's only about 20% soy-based with the rest of the mix produced like polyfoam. The healthiest, least toxic chemical-laden option is to use natural latex rubber foam made from the rubber tree. But in terms of cost-effectiveness, reusing your chair's old foam is the winner. Again, if your chair came from a smoker's house or has cat pee on it, look into buying new foam; otherwise reusing the original stuff is the cheapest and greenest option.
I reused all my old foam and batting for the Chevron Chair cushion, arms, and inside back. If you purchase new foam, cut it into the same shapes as the old, using an electric turkey carver. Sounds crazy, but it works. Staple it in place, and cover with batting.
9) Sewing the Deck Cushion
Sewing the deck cushion is just like making the arm covers. Pin and baste welting to the top and bottom pieces first, then sew in place. Reuse your old zipper, if possible, for the middle piece of the cushion cover. Sew the zipper to the middle piece, then pin and baste the middle piece to the top and bottom of cover. Remember to sandwich the welting between right sides of the cushion cover, this time sewing from the side you haven't done yet. With the cushion foam wrapped in batting, stuff it into the new cushion cover and zip closed. You can sew a simple muslin cover to go over the foam and batting first, and then put that inside the upholstery fabric cover, but that is an extra step you may not want to take. I didn't.
10) The Inside Back
Completing the inside back of the chair is one of the easiest parts to do because it requires no sewing. Place chevron fabric right side up (because you marked which direction that was) over inside back foam and batting, making sure the batting looks smooth. Staple in place at top and bottom first (on the backside of the frame), working from the center to the right and left. Distribute taut fabric evenly. Then draw the fabric through the left side and right side and staple the same way. This was when I noticed where all the change from your pockets disappears to over the years. You can reach your hand pretty far back between the decking fabric and inside back fabric.
11) The Outside Back
You're almost done! Staple dust cover fabric over the outside back of the chair frame, the same way you did for the outside arms, and place batting over it. Staple the batting in place and fluff it over the staples. Next, take the remaining welting and staple it, raw edges facing inward, around the outside back of the chair. I stapled welting on the top and sides but not the bottom of the chair back because I wanted the bottom of the chair to look the same on all four sides.
How do you staple the outside back cover of the chair, you ask? You don't. This is where you employ flexible metal tacking strip. It's tricky to use and will definitely bite you, but magically works. Staple the metal tacking strip inside the welting, with claws poking outward at you, but in the center of the chair. You're going to bend these claws toward the welting, grabbing the outside back of the upholstery fabric and enclosing the back of the chair. Bend the claws toward welting with your fingers, then pound completely closed with a rubber mallet.
After finagling the flexible metal tacking strip, the only part of chevron left to staple is the bottom. Work from the center to either side of the bottom of the chair frame like you have before.
12) The Dust Cover
¡Finalmente! You're really almost finished! Carefully turning your chair upside down on a clean surface (you don't want to get the fabric dirty), place dust cover fabric over the bottom of the chair. Tuck raw edges in and staple in place to keep critters out.
13) Reattach Chair Legs
Lastly, importantly, reattach your chair legs by screwing them in place through the dust cover fabric. Dust cover fabric is not super strong and easily tears. But that's ok, because you need to have chair legs go through it. Once the legs are secure, turn your chair over, and sit in it. Revel in a job well done.
You can use these instructions as a supplement to a book about upholstery, such as Furniture Upholstery by Sunset Books. I also HIGHLY recommend taking an upholstery class at your local community college. Hands on experience with a teacher at an affordable price + whatever you spend on fabric and tools you'll keep. Happy upholstering!