Folding chair straps don't usually last as long as aluminum frames. To reattach the seat and back, nylon cord works best because it is strong and weather resistant.
Use a screwdriver to remove the old straps from the chair frame.
Use steel wool to gently clean the chair frame. If the chair has wooden arms, sand lightly to prepare for new paint or stain.
Tie a double knot in the bar through the seat with the craft string. Place your craft ball of string on the ground inside the seat frame throughout the weaving process.
Bring the rope behind the folding bar on the seat. Continue around the back of the chair, then loop the rope over the bar (by the headrest) and bring it forward from the back. Just like if you were to weave on a loom, you are creating your "warp" at this point.
Route the cable to the seat that goes under the center seat bar. Bring the rope under the lower tie bar and over creating another loop. Again, use the widest part of your second hook to hold your loop.
Go back to the top, again behind the center seat bar, over the top bar and push the loop between two ropes. Grab the new loop with your crochet hook and pull it through to start the chain stitch that will run across the top of your chair. Use the wide part of your crochet hook again to hold this new jump and lower the pattern.
When you have finished your 'warp' and covered the entire chair vertically, take the last strand and cut it long enough to make one last loop. Bring your last loop to the outside to lock it. Thread and tie a double knot.
Trim off any excess wire and use a flame to seal.
At this point the horizontal pieces of the chair are complete.
Creating the 'raster' or the horizontal part of the chairs is exactly the same process. Again, you'll want to use your large needles to create a single chain stitch near the horizontal bars of the chair to anchor everything.
As the chair backs are woven, consider adding patterns and colors, like a pineapple or cactus. Maybe glue on some pom poms just in case..