How do I get the black streaks off the outside of my gutters?

What are the black streaks on the outside of gutters?

The black vertical streaks on the face of a gutter are called tiger stripes. They start at the front lip and run down toward the bottom edge in bands, and they show first on white and light-colored aluminum because the contrast is highest. Painted gutters across Macomb and Oakland County pick them up as they age. Removing them is often sold as gutter brightening or gutter whitening.

Tiger stripes are a film of asphalt and pollution residue bonded to the gutter paint. Rain washing off an asphalt shingle roof carries fine asphalt particles and oils, along with soot from traffic and chimneys that settled on the shingles between storms. When that water runs over the front lip and down the face of the gutter, it leaves a thin layer of residue along its path. The next rain follows the same path and adds another layer, so the bands darken season by season. The stripes are a different problem from the algae streaks on the shingles above, which our post on black streaks on a roof covers.

Why won't the black streaks on my gutters scrub off?

Tiger stripes resist scrubbing because the residue is bonded to the paint rather than sitting loose on top of it. Ordinary dirt on a gutter face rinses off with a garden hose. Stripe residue is oily and very fine, and heat and time make the film harder to lift. Plain water beads off the film, and dish soap with a sponge usually lightens a stripe without removing it.

The age of the gutter paint changes how stubborn the stripes are. Factory gutter paint is a baked-on finish that stays smooth for years, then slowly oxidizes and turns chalky. A quick test tells you where your gutters stand: wipe a finger across a clean section of the face, and a white smudge on your fingertip means the paint has oxidized. Residue settles into that chalky layer, and on older gutters a faint outline of the stripe can remain after a correct cleaning.

Why does a house wash leave the gutter streaks behind?

A house-wash mix leaves tiger stripes behind because it is built to kill living growth, and the stripes are not alive. The solution used in soft washing is a biocide with a surfactant that helps it cling to vertical surfaces. It breaks down algae and mildew, and a low-pressure rinse carries the dead growth away. Asphalt and soot residue contains nothing for a biocide to kill, so the black film stays on the paint.

Tiger stripes stand out right after a house wash. The vinyl comes out bright, the soffits come out clean, and the gutter faces still carry gray-black bands. Any green film on the gutters comes off with the siding, because that part is algae. The stripes need a different cleaner and a brush, so we list the gutter faces as a separate line on a house washing quote rather than expect the siding mix to handle them.

How do you remove tiger stripes from aluminum gutters?

Tiger stripes come off painted aluminum gutters with a surfactant cleaner made for gutter faces, a soft brush and a short dwell time. The surfactant loosens the oily residue from the paint film. The brush then lifts the residue without cutting into the finish. The work goes a few feet at a time, with a rinse before the next section.

Dwell time on a gutter face stays short. The surfactant cleaner goes on, sits long enough to loosen the stripe residue, gets brushed and gets rinsed before it has a chance to dry. Gutter cleaner that dries on painted aluminum can leave dull marks of its own, especially on a south or west face in afternoon sun. Working the shaded side of the house first and keeping each section wet until the rinse keeps the finish even.

A soft-bristle brush on an extension pole does the lifting on a gutter face. The bristles follow the curves of a K-style gutter, where stripes hang on longest in the grooves. Once a surfactant cleaner has loosened the stripe residue, light pressure on the brush is enough.

A homeowner cleaning a single-story run of gutter can use a surfactant cleaner, a soft brush and a short dwell. Test the cleaner and brush on a short section near a downspout first, and check the paint after it dries. If the paint looks duller than the surrounding face, stop, because the finish is thin or oxidized and more scrubbing will wear through it. Gutters above the first story mean working from a ladder with a wet brush pole, which calls for a ladder stabilizer and a second person at the base.

What should you not use on painted aluminum gutters?

Scouring pads, abrasive sponges and solvents remove tiger stripes by removing the paint under them. Factory gutter paint is a thin coat, and a green scrub pad cuts through it quickly. A melamine foam sponge is a fine abrasive and can polish the finish flat, leaving a dull patch next to glossy paint, especially on older or oxidized paint. Lacquer thinner, acetone and similar solvents soften the paint and can take it down to bare aluminum. A spot that has lost its paint oxidizes, holds new residue faster and does not clean back to the original color.

High-pressure water is a poor fit for gutter faces. A pressure wand at close range can dent thin aluminum, lift paint along seams and end caps, and push water behind the gutter at the fascia. Pressure also leaves most of the bonded film in place, because the residue needs a surfactant to let go of the paint.

Why do clogged gutters cause new black streaks?

Tiger stripes form where water sheets over the front lip of the gutter, so a clogged gutter makes new stripes. A clear trough carries most rain to the downspout, and less water crosses the lip. When leaves, maple seeds and shingle grit pack the trough or block a downspout, water backs up and spills over the front edge, carrying roof residue down the face. Each new stripe marks a spot where water went over the edge.

The location of the stripes on a gutter points to the cause. Heavy striping along one run often means a clog near that downspout, a section that has lost its pitch, or a loose hanger that has let the gutter sag. Stripes below a roof valley mean concentrated runoff is overwhelming the gutter at that corner. A sagging or flat run is one we can rehang and re-pitch, and the fault often goes back to the original install without the owner ever knowing. Our list of signs your gutters need cleaning covers the warnings that show up alongside fresh stripes.

Michigan weather makes gutter overflow a regular event. Mature tree canopy across Macomb and Oakland County fills troughs with seeds in spring and leaves in fall. In winter, ice in a blocked gutter sends meltwater over the lip during each thaw, and freeze-thaw cycles work hangers loose. Homes near Lake St. Clair and the inland lakes stay damp longer, and shaded gutter faces there pick up green algae on top of the stripes. Cleaning the faces without clearing the trough leaves the cause in place, and new bands start with the next heavy rain.

How can you tell tiger stripes from algae or chalky paint on a gutter?

Tiger stripes are dark vertical bands from the lip down, algae is a green film on shaded faces, and oxidized paint is a white chalk that rubs off on a fingertip. Each one needs a different approach.

How much does it cost to clean gutters and gutter faces in Macomb County?

Gutter cleaning with Macomb Power Washing Solutions starts at $149 and covers hand removal of debris, downspout flushing and a flow test on every downspout. Removing the tiger stripes from the gutter faces is quoted as its own written line item, priced on linear feet of gutter, number of stories and how set the stripes are. Face cleaning pairs well with a house wash, which starts at $349, since the ladders and crew are already at the house.

Work on a combined gutter and house-wash visit runs from the top down. The trough gets cleared and the downspouts flushed first, so no debris washes over a freshly cleaned face. The gutter faces get their surfactant cleaning and brush work next. The siding gets its soft wash last, so any drips from the gutters land on a wall that is about to be washed. Every quote arrives in writing within 24 hours, with no travel fee anywhere in the 87 communities we serve across Macomb, Oakland and St. Clair counties, Grosse Pointe and Harper Woods.