You don't have to put those plastic lawn chairs out on the curb just because they no longer look brand new. Instead, revitalize them with a thorough cleaning treatment and a secret substance for a factory-fresh shine: car wax.
If the chairs have sat unused outside or even the garage for months on end, they may be covered with cobwebs, dust or dirt. Wipe them off with a dry rag or soft brush to remove all the loose debris; brush off the underside area as well. Spray the chairs down with a mist of the garden hose; then select a "jet" or powerful spray setting to knock off any dirt trapped in the textured plastic resin.
Sometimes, dirt bakes into the plastic a bit, or the plastic becomes discolored from pollution and particles into the air. If those chairs still look unsightly after a spray of the hose, wet them again; then rub them down with a nylon scrub pad. These pads remove gray discoloration that sits on the surface of the plastic. Follow up with a little baking soda sprinkled on a wet sponge to remove excess dirt. An old toothbrush reaches into the grooves and textured areas molded into the chairs. Baking soda serves as an alternative to harsh chemical cleaners that may damage or bleach the plastic resin.
Sometimes the discoloration is so embedded in the plastic that even a mild abrasive doesn't remove it. In this case, a power washer often does the trick. Select a gentle setting on the power washer at first to avoid damaging the chair; try several different settings until you find one that cleans the chair well without carving grooves into it. The power washer removes a thin layer of plastic and may leave the surface a bit rough in some areas. If this happens, sand the chair smooth with a fine-grit sanding block.
Restoring the Shine
Once the chair is clean and smooth again, it's ready for a wax treatment. Rub an automotive paste wax over the chairs with a soft rag, allowing it to set for several minutes or as recommended on the packaging. Wipe off the excess wax with a clean soft rag afterwards. Do not wax the chairs if you think you'd like to paint them eventually, as the wax prevents the paint from adhering well.