Hose down lawn chairs periodically to remove grime; scrub stubborn dirt with detergent. At least once a year, clean the exposed aluminum frame with 000 steel wool and kerosene; renew pitted areas with an aluminum cleaner. Wax the frame with car paste wax. Check frequently for loose fasteners and tighten them.
Kits for replacing broken plastic webbing are available at hardware stores and home centers. To measure for a replacement strip, stretch the webbing taut across the chair frame from screw hole to screw hole, then add 3 1/2 inches (for reinforced ends). At one end make a 45-degree fold, then another, forming a triangular tip.
Using a leather punch, make a hole 3/4 inch from the apex of the triangle. Insert a washer head sheet-metal screw (these come with most kits) through the hole; then screw it into the fastener hole in the chair frame.
Weave the webbing so that it duplicates the position of the broken strip; fold and fasten the other end as before. For chairs that take clip-type fasteners instead of screws, follow the instructions on the kit package.