Spending a little time each fall performing some maintenance and repair--along with a good cleaning--will keep your chairs looking good for years to come.
Turn the chair upside down. If the damaged straps are held on by metal screws, remove the screws; for plastic rivets, pop them off with a flathead screwdriver. For fasteners inside a slot in the frame, cut the strap with a utility knife very close to where it goes into the slot. The fastener should then fall loose.
With a measuring tape (or a length of twine you can measure later), measure the length of the strap you'll need. The tape or twine will need to go over the hole or slot in the frame, around the frame, over to the other side, and then around the frame again to cover the opposite hole or slot. Pull as tight as you can when measuring.
Cut a length of strap 1 inch (2.5 cm) shorter than your measurement. This will ensure that you stretch the strap as tightly as possible when installing it.
With an awl or the point of a screw, make a hole about 1/4 inch (6 mm) from each end of the strap.
Attach one end of the strap with a sheet-metal screw (see A). If you are using plastic rivets, you'll need to drive them in with a rubber mallet or very gently with a hammer. Loop the other end of the strap around the other side of the frame, pull tightly and attach in the same manner. Replace any other straps as necessary.
With a screwdriver, remove the screws or metal clips holding the webbing. If only one or two straps are torn and the rest look good, you may want to replace only them. If the chair has a drooping seat or many frayed straps, you'll need to remove all the webbing.
Using the method described in step 2, above, measure the distance from the slots or holes for each of the horizontal straps. Remember, the chair back and seat may not be the same width, so take measurements for each.
Unroll a length of nylon webbing. If you are attaching the horizontal straps with screws, add 2 inches (5 cm) to each measurement, and cut the roll into strips of that length with scissors. If you are using clips, add 1 1/2 inches (4 cm).
For chairs with screws, fold down the corners at one end of the strap to form a point (you'll be able to see from the old webbing how this is done). Make a hole with an awl or screw about 1/2 inch (12 mm) from the tip of the point. Screw in one end of the strap, pull it around tightly, and screw in the other end.
If you're using clips, fold 3/4 inch (2 cm) of strap around the clip and insert it in the slot (again, you should be able to see from the old webbing how to do this).
After all the horizontal webbing is done, install the vertical webbing using the same methods as above. You'll need to weave the vertical straps in and out of the horizontal webbing (see B). Make sure the vertical straps all run behind the bar that is the pivot between the back and the seat.