Sweep the entire metal roof with a push broom to loosen and eradicate dirt, leaves, twigs and other rubble. Scrub any corrosion patches vigorously with a wire brush until all scale is eradicated, then sweep the loosened corrosion and the other rubble off the roof.
Spray each metal roof panel with water from a garden hose. Thoroughly rinse the roof before tarring it to ensure proper bonding. Let the roof air dry for 24 hours.
Open the container of wet-stick fiber roof coating, then stir the tar with a paint stir stick. Pour the tar into a paint tray.
Roll the tar onto the edges of the metal roof using a long-handled nap roller. Apply the tar to the entire perimeter of the roof, then cut tar in around chimneys, skylights and other penetrations using a paintbrush.
Fill in the rest of the metal roof with the tar, using the nap roller. Apply the tar in even, back-and-forth passes across the width of the roof, starting at one end and working across the length of the roof. Use 1 gallon of tar per 100 square feet of metal roofing.
Let the coated metal roof cure for two to three days.