The way to Remove Mildew From Painted Rails on a Porch
Mildew on decorated porch rails generally occurs because of moisture buildup and a lack of sunlight. Mildew spores thrive in such conditions and leave behind dark, brown, gray or green spots that give off a foul, musty odor. Chlorine bleach kills mildew spores, washes away dirt and brightens surfaces, so it is great for removing mildew from painted surfaces. Regularly cleaning painted porch rails can enhance their appearance and help prevent future mildew or mold development.
Fill a bucket with 1 part liquid bleach and 3 parts water.
Don gloves and safety goggles. Dip a soft-bristled nylon scrub brush into the bleach solution and then scrub the painted rails to remove the mildew and any other deposits. Wash the brush in the bucket as you go. When you are finished scrubbing, let the diluted bleach to sit down around the surface for 10 minutes.
Wash the bleach in the rails using a garden hose along with a cloth dipped into a clean bucket of water. Permit the rails to air dry.