Scrub the rust on the metal lawn table with steel wool. Brush the loosened rust from the table with your hand. Continue scrubbing and removing as much of the rust as possible.
Apply 2 tbsp. of phosphoric acid to the remaining rust stain with a small sponge. For large rust stains, apply additional acid. Follow instructions on the phosphoric acid container as to how long to leave the acid on the rust stains.
Wipe the acid from the metal table with a clean rag.
Sprinkle baking soda on the area to neutralize any remaining acid. Allow the baking soda to remain on the table for 20 minutes.
Rinse the baking soda from the table with buckets of water or water from a garden hose. Dry the lawn table with clean rags.