Buy a can of lacquer in the spray paint section of the hardware store.
Make sure the humidity is low the day you plan to waterproof your lawn furniture. The temperature should be between 50 and 85 degrees.
Remove all the loose dirt from the item with a brush. Sand with 220 grit paper and wipe down with a tack cloth. Make sure all dirt, grease, and oil has been removed.
Cover your work area with a drop cloth.
Begin spraying the air next to the item and sweep sideways until you are spraying the air on the other side of the item. Apply several thin coats. This will help you to avoid drips, runs, and having more lacquer in some areas than in others.
While the lacquer should be dry in 15 minutes, do not handle for 24 hours.