Clean the surface using one (1) gallon of bleach and three (3) gallons of water. Spread all over your surface. With clean water from a regular garden hose or pressure washer, rinse the bleach and let it dry for 24 hours.
Identify cracks, gaps, seams and fix it with Lanco® AQUA-PROOF PREP™
Using a 3/4 nap roller, pour some roof coating on the surface and spread it in one (1) direction. When the the roller starts rolling, add more roof coating to the surface. Let it cure for 24 hours.
Repeat step four (4) but this time crisscrossing the first coat.