What will clean black streaks off gutters?

If you don't have a pressure washer, Krud Kutter comes in a spray bottle. Spray it, let it sit, then use a nylon scrubbing pad and it will be removed right away. Another excellent product is bleach mixed with Jomax. This will discolor the stripes.

Gutter Zap is another effective option for removing black gutter streaks caused by electrostatic bonding of tar and asphalt from roofs. The black spots on the gutters come from dirty runoff from the roof. Dirt is a mixture of dirt, decaying leaves and asphalt from shingles. Removing it is quite simple, since you have the right tools and equipment.

The gutters are, of course, a painted surface, typically powder-coated. There is a transparent protective coating on top of the paint. Unfortunately, the quality of the installed gutters can be very different. Gutters that show black stripes early in life are a good sign of low-quality painted aluminum gutters.

The transparent coating layer offers no protection and the sun can oxidize the surface of the aluminum. Then, tar and dirt from roof runoff get stuck in that oxidation layer. Just spray it, let it sit for a few moments, and then wipe it with a clean, damp cloth or rinse with clean water. Often referred to as “tiger stripes” or “zebra stripes” by industry insiders, those ugly black spots on gutters are the result of a chemical reaction between the asphalt in the roof shingles and the anodized aluminum in the gutters.

Unless you have a 1-story home, you'll need to climb to get to the gutters on the second floor, even with extended cleaning tools. In this case, if the gutters are gray or dirty, you may not be able to clean them back to their original white and you may be forced to replace them to regain their original shine. Be careful if the protective seal of your gutter is missing; in that case, you may not be able to clean the tiger stripes and you may have the option of replacing the gutters completely. Cleaning gutters can be an arduous task that you may not want to do, but it's important in the long run.

A yearly cleaning with any of these products will almost guarantee stain-free gutters for years to come. Unfortunately, even if gutters are cleaned, black stripes are likely to return within 1 to 3 years.