Pour 1 gallon of warm water, 3/4 cup of bleach, and 1 tbsp. of laundry detergent into the bucket. The laundry detergent and water will clean away the white powder if it is dust or pollen, and the bleach will get rid of the white powder if it is mold.
Use the sponge to wash the lawn chairs off with the cleaning solution. Wipe down the chair slats, applying gentle but firm pressure. Don't forget to turn the lawn chair over and wash underneath the seat. Switch to a scrub brush for any spots that are not coming clean with the sponge.
Let the cleaning solution remain on the chairs for 15 minutes after you finish scrubbing them clean.
Turn your garden hose on and rinse the cleaning solution off of the lawn chairs.
Dry the lawn chairs with a towel, or allow them to air dry in the sun.