Put on rubber gloves. Gently brush the beach chairs with an upholstery brush to remove loose mildew and dirt.
Fill a bucket with a pint of hot water. Add one tbsp. of perborate bleach to the water and stir to mix. Sodium perborate is a white, odorless compound used for bleaching and oxidizing.
Wet a sponge in the solution, and scrub the mildewed areas of the chairs. Leave the solution on the mildewed areas for half an hour.
Rinse the chairs with a garden hose. Leave the beach chairs out in the sunlight to dry fully before you use or store them.