Instead of junking your old sling back chairs replace the backs for a fraction of the cost of replacing either the patio set or premade slings.
Step 1: Removing the Old Slings.
I started by removing the sling on the back of the chair. To do this you must remove the garnishing bezel that covers the bolts on the back of the chair. The bezel hooks on the stretching bolts at the back of the chair.
Step 2: Cutting the Back
The easiest way to pop the bezel over the stretching bolts is to cut the back. Due to the material being pretty rotten I easily cut through it with a serrated knife. I then used a flat head screw driver to lift the bezel over the bolts for easy removal.
Step 3: Desplining the Back and Measuring
The next step is to unscrew the stretching bolts that were under the bezel. Make sure not to lose the washers. Set them in a safe place and start desplining. There are two pieces of spline on each sling. (If you're not sure what spline is its a hard plastic rod that keeps the sling from coming out of the retaining brackets.)
Start with the bottom spline, push the fabric into the gap to loosen the spline and then pull it sideways and out. You can also use a screwdriver to push the spline out and remove the fabric from the stretching bracket.
Next take your screwdriver and insert it into the pocket in the top of the sling and pull it back loosening the fabric on both sides then push the spline out with your screwdriver. Once about an inch of spline is exposed you can use pliers or vice grips to pull it out. Feed the fabric back and your top section is removed.
Now take your removed back undo the seams and get your total size for your pattern.
Step 4: Fabric Selection and Sewing
For the fabric you will want a UV resistant fabric rated for sling chairs, I used Sunbrella. Pay attention to the grain of the fabric you will want it to match for both slings. For sewing the fabric make sure you use a leather needle and UV resistant thread (don't forget to fill the bobbin also). Last thing you want is your thread to break.
Next check your completed replacement against your old back. Now lets get to installing!
Step 5: Installing the Back Sling
Now that we have measured the back make not of any taper to the piece so you don't install it upside down. Insert the spline and slide the bottom into the stretching bracket.
Once the bottom is in place tuck the top through the slot in the top of the seat and respline. Make sure the fabric is centered on the stretching bracket and the top of the back also check centering of your spline.
Align your holes for the bolts as well as possible (starting with the center) then apply vice grips to hold it in place. Start the bolt then move to either of the side bolts. Apply the vice grips on the inside(towards center) of the bolt and start it. Then repeat process on other side. Now that all the bolts have been started we can begin tightening the back. Place the vice grips on the outside of the bolt and align as much as possible. Repeat on other side. Once the sides are secure tighten center bolt and replace bezel cover. The back is now installed and finished!
Step 6: Now to the Bottom
Remove the bottom of the chair from the frame, mine was four bolts. Once free of the frame roll the two sides outward and remove the spreader bar. Now that the tension is relieved the fabric can be pushed into the slot to free up the spline. Work out about an inch of spline and pull out with pliers. The sling should then slide easily slide out if not just feed a little more into the slot. Again as before remove all seams and create pattern, cut fabric to match. Check against old piece.
Step 7: Stretching the Bottom Sling.
Install your spline into your replacement sling and insert it into the chair rail, again check for tapering front to back so you don't install it backwards, take your time and line everything up with the front of the chair. Once everything is in place you will notice the spreader bar will not fit back in place. Now you can rent a professional sling chair stretcher for $25.00 plus a deposit, you can buy one for $100.00, or you can make one for $3.00. I decided to make one. I bought a set of hinges (you may have one laying around) and a 2x4. I cut the 2x4 to a length just short of the spreader bar, cut it in half and installed the hinge on one side. I started stretching at the front of the seat by placing the bent jointed 2x4 on the inside of the chair rails then pressing down to straighten the board and stretch the material if you have a hard time doing this you can even use a foot. This started stretching the fabric, I then moved right next to the hole in the chair rail for the spreader bar and easily installed it.
Step 8: Finishing Up.
Now reinstall the bottom sling. Start by using the bolts in the back to secure and spread the sling then secure the front and.... you guessed it you're done, with one at least, now do it five more times for the rest of the patio set. To redo the whole patio set I have which is six chairs it cost me approximately $115.00. not too bad.