Fill a pump sprayer with 1 part bleach and 3 parts water.
Spray down plants and shrubs surrounding your home with plain water from a garden hose. This protects them from any bleach solution that may fall off of the roof.
Spray down the roof with so that it is damp and then spray the bleach solution evenly onto the shingles.
Wait 15 minutes for the solution to break up mold, grease and oil on the shingles and then scrub down the shingles with a plastic push brush.
Rinse the shingles clean with water. Wait for the roof to dry completely before continuing the project.
Stir the asphalt sealant thoroughly and then pour it into a cleaned pump sprayer.
Spray the sealant evenly onto the shingles in a thin layer to avoid puddling. Once you have applied the sealant, gently roll it into the shingles with a paint roller.
Wait two hours for the sealant to dry and then apply a second coating. The coating will dry fully within two hours.