Black Streaks on Gutters: What Tiger Striping Is and How to Remove It

What the stripes actually are, and why they run vertically

Run your hand down a streaked gutter and there is nothing to feel. The stripe is a film, not mud. Asphalt shingles shed fine bituminous particles as they weather, and roofs also collect carbon from vehicle exhaust, pollen, and airborne dust. In a hard rain, water launches off the drip edge and lands in the trough. In a light rain, and at the start and tail end of every storm, the flow is slow enough that surface tension pulls it around the outer lip and down the face instead. That water carries the roof's residue with it, evaporates on the painted aluminum, and leaves the solids behind. Repeat that a few hundred times and the residue bonds to the slightly oxidized finish. The rivulets follow the same paths every storm, which is why you get stripes instead of an even gray.

Why a pressure washer is the wrong tool for a gutter face

Residential seamless gutter stock is thin, commonly .027 inch aluminum, and contractor-level pressure will dent it, oval the face, and drive water up behind the drip edge into the fascia. High pressure also cuts the baked enamel, and once you have chewed the finish off a section the whole run reads uneven from the street permanently. Pressure also does not solve the actual problem. The striping is chemically bonded, not loose, so blasting takes the top layer and leaves the ghost underneath. People spend an hour on twenty feet, watch it look great while wet, then watch the stripes come back as it dries. The other common failure is a strong acid brightener left to dry in the sun, which bleaches the finish in patches and leaves light-colored zebra marks that are harder to live with than the original stripes.

What actually removes it: chemistry, dwell, and a soft brush

Rinse the face with plain water first so the cleaner is not fighting dry dust. Apply a gutter-specific cleaner, meaning an alkaline surfactant blend built to release bituminous residue, at low pressure, working bottom up so nothing runs dry. Then let it dwell. Dwell is the step everyone skips. The film needs several minutes to release its grip before anything you do with a brush matters. Agitate by hand with a soft vehicle-style brush, one ten-foot section at a time, and rinse that section top to bottom before the cleaner dries on it. Wet the landscaping down before you start and again after, because runoff lands on whatever is planted along the foundation. Set ladders on level footing and never lean one against the gutter itself. A gutter is a drainage channel hung on hangers, not a structural rail.

When the stripes will not fully come out

Two conditions cap the result, and anyone honest tells you before they start. The first is oxidation. Painted aluminum chalks as the coating breaks down. Rub a dry section with a clean rag, and if the rag comes away with white powder on it, the finish is failing. Cleaning will pull the striping and the loose chalk together, which can leave that run a shade flatter than the shaded sections beside it. The second is stripe age. Residue that has baked onto a south or west face for eight or ten seasons works into the surface texture, and you may recover eighty or ninety percent of it rather than all of it. Test one section near a downspout before committing to the whole house. If the test only lightens, the honest answer is repaint or replacement, which is gutter contractor work, not cleaning work.

How to judge any company quoting this work

Four questions sort it out regardless of who you call. First, will they test a section and show you the result before pricing the full perimeter? A flat number given sight unseen means nobody looked at your finish. Second, what pressure do they put on the gutter face? Anything described as blasting or stripping should end the conversation. Third, does the quote cover the gutter exteriors only, or does it also include clearing out the troughs? Those are two different jobs, and assuming you were getting both is the most common invoice surprise in this trade. Fourth, will they email a certificate of insurance without being chased. Then consider hiring nobody. A single-story home with an accessible perimeter is a real Saturday project: cleaner, soft brush, extension pole, hose, step ladder. If that describes your house, do it yourself.

How Reflekt handles gutter faces, and where we come up short

This is exterior surface cleaning, so we run it off the same soft-wash setup as house washing at $0.18 per square foot, quoted after we look at the elevations. Nobody goes on the roof for it. Two things worth being clear about. Our window cleaning uses 100 percent pure deionized water with no soap and a RainShield finish, but a bonded bituminous stripe will not release with water alone, so gutter faces get a detergent process instead. Different problem, different method. And this is not gutter cleaning, which starts at $199 and means clearing the troughs and downspouts. Where we are behind: Hunter Stevens and Ethan Seusy started Reflekt in April 2025, so we have 115+ Google reviews at 4.9 stars and about a year of history, less than several long-established valley companies. If decades of track record decides it for you, hire on that. Otherwise call (208) 453-6760.