How Do You Remove Black Stains from Gutters? 5 DIY Recipes Ranked by our local Rockford crew

Those black vertical streaks on the outside of your gutters have a name: tiger striping. They're not technically dirt, which is why a quick rinse with the garden hose never seems to get them off. Tiger stripes are a chemical bond between electrostatic dust, acid rain residue, asphalt shingle granule runoff, and (on north-facing or damp-shaded runs) microscopic algae and mildew. They build up a little with every rain, so by the time you can see them from the street they're well bonded to the gutter face.

The good news: most tiger stripe stains come off with cheap household chemistry, no special equipment, in a Saturday afternoon. The bad news: old, heavy stains sometimes leave a permanent shadow in the finish that only repainting or replacement will hide. Below are 5 DIY recipes ranked from cheapest to strongest, with what each removes, what doesn't, and when to give up.

Recipe 1: Vinegar + Dawn dish soap — start here (cost: ~$3)

What you need: 1 gallon warm water, 1 cup distilled white vinegar (5% acidity), 1/4 cup Dawn dish soap, a 5-gallon bucket, a soft-bristle brush or microfiber pad on a telescoping handle, garden hose, ladder, rubber gloves.

What it removes: Light tiger stripes and surface film, mild algae streaking, and hard-water spots from sprinkler overspray. If the stripes are still there after two or three passes, move up the ladder.

Process: Mix the vinegar and Dawn into warm water. Hose down the stained gutter exterior to wet the surface — never apply cleaner to a hot, dry gutter (it'll dry instantly and leave a residue). Sponge or brush the mix onto a 6–8 foot stretch of stained gutter, let it sit 2–3 minutes, then scrub with the soft brush in long horizontal strokes. Hose-rinse from the top. Move to the next section. Repeat the cycle 2–3 times on stubborn stretches if needed.

Why it works: Vinegar is a mild acid and Dawn is a surfactant: together they loosen the film on the gutter face and carry it away when you rinse, instead of just smearing it around. Give it the 2–3 minutes before you scrub — scrubbing straight away gives the mix no time to work.

Recipe 2: Oxalic acid wood-bleach wash — for rust stains (cost: $10–$18)

What you need: A 12 oz tub of Savogran Wood Bleach (oxalic acid crystals, $10–$18 at hardware stores), water, a plastic bucket, soft brush, garden hose, rubber gloves AND goggles (Savogran's label calls for both).

What it removes: Orange-brown rust stains bleeding from steel hangers and screws, and iron spots from well-water sprinkler overspray. Use it on rust, not on the grey-black stripes themselves — Recipes 1, 3, 4 and 5 are made for those.

Process: Savogran's label gives two strengths: the whole tub in one gallon of hot water for bleaching wood, or in four gallons of water for brightening a deck. On a painted gutter, use the weaker four-gallon strength (about 3 oz of crystals per gallon) and test a small hidden spot first. Wet the gutter, brush the solution onto the rust stain only, let it work a few minutes, then scrub gently and rinse thoroughly — the label says to rinse three times. Wet nearby plants before you start and rinse them again afterwards, and work in cool, cloudy weather so the solution doesn't dry on the gutter.

Safety: Oxalic acid is harmful if swallowed or absorbed through the skin and can cause serious eye damage. Wear goggles and rubber gloves, avoid breathing the dust while you mix the crystals, and never mix it with chlorine bleach or other chemicals (Savogran's label says the same). If it gets on your skin, wash with soap and plenty of water; if it gets in your eyes, rinse with water for at least 15 minutes and get medical help.

Recipe 3: Krud Kutter Original, diluted — for mildew and road grime (cost: $8–$13)

What you need: A 32 oz bottle of Krud Kutter Original Concentrated Cleaner/Degreaser ($8–$13 at Home Depot, Ace and other hardware stores), a bucket, soft brush, garden hose, gloves and safety glasses (its safety data sheet lists it as an eye and skin irritant).

What it removes: Mildew stains, green-black algae film, grease, tar and oily road grime — useful on gutters near busy Rockford roads like Riverside, Alpine or State Street. Rust-Oleum's data sheet recommends it for aluminum siding and gutters.

Process: Rust-Oleum lists aluminum under its all-purpose strength: 1½ cups of concentrate per gallon of water. Full strength is the label's heavy-cleaning setting, for jobs like grills and engines. Test a hidden spot first and wet nearby plants before and after (both on the data sheet). Wet the gutter, apply with the brush, let it work a few minutes without drying, scrub gently, then rinse from the top.

When to use it: When the staining is organic — green-black patches on north-facing or tree-shaded runs — or oily film from traffic. Skip TSP (trisodium phosphate), the old-school alternative: it can darken and corrode aluminum and strips the sheen from painted surfaces. For plain grey-black tiger stripes, Recipe 4 is made for the job.

Recipe 4: Krud Kutter Gutter & Exterior Metal Cleaner — made for black streaks (cost: $13–$18)

What you need: A 32 oz trigger sprayer of Krud Kutter Gutter & Exterior Metal Cleaner ($13–$18), a soft brush or cloth, garden hose, gloves and safety glasses (the label lists it as an eye and skin irritant).

What it removes: Rust-Oleum formulates it for black streaks, oxidation, mold, mildew, algae and grime on exterior metal, vinyl and aluminum — gutters included. It contains no bleach or ammonia and is water-based, biodegradable and non-flammable. One bottle covers about 50–75 square feet.

Process: Test a hidden spot first and pick a day with little to no wind. Spray the stained section, let it work for two minutes, and don't let it dry on the surface. Wipe or scrub with a soft brush, rinse, and repeat if needed — those are Rust-Oleum's directions. No mixing, which is the advantage over Recipes 1–3.

When to use it: When vinegar hasn't cleared the stripes. One warning from the data sheet: years of sun can fade or oxidize gutter paint, and once the dirt is gone that damage can show. The cleaner reveals it — it doesn't cause it.

Recipe 5: Gutter Zap concentrate — the contractor-grade option (cost: ~$26)

What you need: A 32 oz bottle of Gutter Zap Residential (about $26 online), a pump sprayer, soft brush, garden hose, gloves and safety glasses.

What it removes: Its maker, Exterior Inc., formulates it to remove black streaks caused by the electrostatic bonding of tar and asphalt, and sells it for factory-painted metal such as gutters. It's a biodegradable concentrate.

Process: Dilute it as the label directs, spray it on, scrub old stripes with a soft brush, and rinse with ordinary garden-hose pressure before it dries. Used as directed, the maker says it won't harm vegetation or painted surfaces — test a hidden spot first anyway.

When to use it: For heavy, long-standing stripes that Recipes 1 and 4 haven't cleared, or for a whole house of gutters — a concentrate goes further than ready-to-spray bottles.

What is the best gutter stain remover?

For classic tiger stripes, the best gutter stain remover is a cleaner made for gutters: Krud Kutter Gutter & Exterior Metal Cleaner ($13–$18) is the easiest to find in stores, and Gutter Zap (about $26) is the contractor-grade concentrate. Start with vinegar and Dawn (~$3) on light film, use diluted Krud Kutter Original for mildew and road grime, and keep oxalic acid for rust stains.

Every gutter stain cleaner above uses the same method: wet the gutter face, apply, let dwell 2–5 minutes, scrub with a soft brush, rinse from the top. The chemistry does the work — pressure does the damage.

What NOT to do — avoid these three approaches

1. Chlorine bleach (Clorox, generic bleach)

Tempting because it's cheap and kills mildew. Don't. Chlorine bleach (sodium hypochlorite) is a strong oxidizer that corrodes aluminum, and it harms the lawn and plantings it runs onto. It also does little for classic tiger stripes, because they're bonded grime rather than growth. Gutter-specific cleaners such as Krud Kutter's are sold bleach-free.

2. Pressure washer

Same warning as our companion piece on pressure washing gutters — high pressure can strip the paint off aluminum gutters along with the stripes; Rust-Oleum's own Krud Kutter data sheet warns that water pressure alone may remove paint. You're left with bare aluminum that stains again faster. Use chemistry + soft brush, not pressure.

3. CLR and other calcium, lime & rust removers

CLR is the bottle many people reach for on rust and hard-water stains, but its own label says not to use it on painted, coated or sealed surfaces or on aluminum — which rules out almost every gutter. For rust spots, use oxalic acid (Recipe 2) on the stain only, after a spot test.

What causes black streaks on gutters?

Black streaks on gutters are caused by dirty rainwater running over the front lip of the gutter. On its way down the roof, rain picks up airborne grime (vehicle exhaust, construction dust, pollen) and fine asphalt particles worn off the shingles. Where that water beads on the lip and trickles down the painted face, the residue dries and bonds to the finish, so it builds up in vertical lines that a garden hose won't rinse off.

Four conditions make the streaks form faster and darker:

• Overflow. A clogged gutter or blocked downspout sends dirty water over the lip in sheets instead of drops, so the streaks get wider and heavier where the water spills over.
• An ageing asphalt roof. Older shingles shed more fine material, so streaking speeds up as the roof gets older.
• Air quality. Homes beside busy roads or construction sites collect more airborne grime on the gutter face.
• A weathered finish. Sun and moisture slowly oxidize the baked-enamel coating. The rougher surface holds residue more tightly, which is why older gutters stripe faster.

Is it black mold? Usually not. Most dark streaks on the outside face are bonded grime and roof residue. Algae and mildew look different — greenish-black and patchy rather than striped — and grow on runs that stay damp, such as north-facing or tree-shaded sides.

Match what you see to its cause before you pick a recipe:

Preventing tiger stripes from coming back

After you've cleaned the gutter exterior, three habits slow the return of tiger stripes:

• Wash the gutter exterior every 12–18 months with the Recipe 1 vinegar-and-Dawn mix. Light surface film comes off easily; established stripes take stronger cleaners and more scrubbing.
• Keep the gutters clean inside — a clean interior means less overflow and less drip-down of the granule-and-debris slurry that feeds tiger striping. Twice-yearly gutter cleaning service in Rockford, IL is the simplest answer.
• Watch for roof granule loss. Older asphalt shingles shed more fine material. If you see heavy granule loss — colored grit collecting in the gutters, bald patches on the shingles — the roof is feeding the stripes, and that's a roofing question rather than a gutter one.

When the stain won't come off — repaint or replace

If you've worked through Recipes 1–5 and there's still a visible shadow, the paint itself has likely faded or oxidized under the stain — and cleaning can't put color back. At that point you have two options:

• Repaint — Krylon Fusion All-In-One or Rust-Oleum Universal All-Surface spray paint in a color matched to your trim, applied to a clean, dry gutter. The result is presentable but visibly different from a factory finish.
• Replace — full Gutter Replacement Rockford IL with fresh baked-enamel coil ($1,500–$2,500 for a typical home). Aluminum gutters typically last around 20–25 years, so replacement is the right call if yours are nearing that age anyway, or if several sections show damage beyond the staining. See our Gutter Installation & Replacement Rockford page for full details.

FAQ — Removing Black Stains from Gutters