TL;DR
Tiger stripes are a bonded film of oxidized roofing asphalt and airborne grime, not ordinary dirt, which is why house wash and pressure both fail on them. They come off with a dedicated gutter cleaner, several minutes of dwell time, and hand agitation with a soft brush -- and they will come back, because the cause is on the roof above.
What tiger stripes actually are
Look at a gutter with vertical dark bands running down its face, evenly spaced, darkest near the top. That is tiger striping.
The film is largely oxidized asphalt washed off the roof. Asphalt shingles shed a small amount of their binder over time, especially as they age, and rainwater carries it to the gutter edge. Where water overshoots or drips over the front lip, it deposits that residue in a vertical trail.
Airborne pollutants, road film, and pollen bind into the same layer. The result is a tenacious coating that has chemically adhered to the gutter finish rather than merely resting on it.
That distinction is the whole reason nothing normal removes it.
Source: gutter manufacturer and exterior cleaning industry guidance
Why house wash and pressure both fail
A standard house wash is designed to break down biological growth -- algae, mildew, lichen. Tiger stripes are not biological, so the chemistry has nothing to act on.
Pressure fails for a different reason. The film is thin and bonded, so force does not lift it. What pressure will do is dent thin aluminum gutter stock, drive water behind the gutter and onto the fascia, and knock the gutter out of alignment at the hangers.
People who try harder with a machine usually end up with the same stripes plus a damaged gutter. The job needs a surfactant that emulsifies the oxidized film and then mechanical agitation to release it.
The general chemistry-over-force principle is covered in soft washing and when it applies.
What you need
- A dedicated gutter cleaner or brightener formulated for oxidized film -- this is a specific product category, not a general house wash
- A soft-bristle brush on an extension pole
- A bucket
- A garden hose
- Eye protection and gloves
- Plastic sheeting for plants below
Do not substitute an abrasive pad or a scouring product. Gutter stock is thin painted aluminum, and abrasion cuts through the finish, which then oxidizes and stains worse than the original stripes.
The method
1. Work in shade, or early or late in the day. Cleaner drying on the surface stops working and leaves its own residue.
2. Protect below. Soak plants and grass with plain water and keep them wet. Cover anything you do not want the runoff on.
3. Rinse the gutter face with plain water to remove loose dust and to wet the surface.
4. Apply the gutter cleaner to a section, following the product dilution exactly. Work in lengths of ten to fifteen feet so nothing dries before you get back to it.
5. Let it dwell for the time the product specifies, usually several minutes. This is where the work happens.
6. Agitate with the soft brush. Long horizontal strokes along the gutter run, moderate pressure. You will feel the film release. Re-wet the brush frequently.
7. Rinse thoroughly with a garden hose before moving to the next section, and rinse the fascia and wall below at the same time.
8. Repeat where needed. Heavy, long-standing striping often takes a second application rather than harder scrubbing.
Clean the soffits and fascia in the same pass while you are up there -- the method is in cleaning soffits and fascia without water intrusion.
Safety, and why this job stays on the ground
Use an extension pole, not a ladder, wherever you can reach. Brushing a gutter run from a ladder means repositioning it every few feet, and repositioning is when ladder accidents happen.
Never operate a pressure washer wand from a ladder under any circumstances. The recoil is a fall hazard with nothing to brace against, and gutters do not need pressure anyway.
Wear eye protection. Gutter cleaners work by chemistry and will sting badly if a drip lands in an eye while you are looking up.
Never combine a gutter cleaner with a bleach-based house wash on the same surface without a thorough rinse between them. Many gutter brighteners are acidic, and acid plus bleach releases chlorine gas. Finish one product, rinse until the runoff is clear, then move on.
Managing expectations
Two honest points.
Some striping is permanent. If the film has been on long enough to etch or oxidize the painted finish beneath it, cleaning removes the deposit but leaves a shadow. Older gutters on older roofs often clean to better rather than to new.
It will come back. The cause is asphalt shedding off the roof above, and cleaning the gutter does not change that. Expect to repeat this annually or every couple of years, and expect faster recurrence as the roof ages.
An aging roof that is shedding heavily is also shedding granules, which is a different signal entirely -- see what causes moss and algae on a roof.
While you are there, check the inside
The outside of a gutter is cosmetic. The inside is functional, and it is the one that causes real damage when neglected.
Overflow from a clogged gutter runs down the fascia and the wall, saturates the soil at the foundation, and can back up under the roof edge. If the outside is striped, it is worth confirming the inside is clear at the same time.
Doing that safely from the ground is covered in cleaning gutters and downspouts without a ladder risk.
FAQ
What causes tiger stripes on gutters?
A film of oxidized asphalt shed from the roof shingles, combined with airborne grime and pollen, deposited in vertical trails where rainwater drips over the front lip of the gutter. It is a bonded chemical film rather than loose dirt, which is why it forms in evenly spaced bands.
Why will not house wash remove gutter stripes?
Because house wash is formulated to break down biological growth such as algae and mildew, and tiger striping is not biological. It needs a surfactant designed to emulsify oxidized asphalt film, plus hand agitation to release it from the painted surface.
Can you pressure wash tiger stripes off gutters?
No. The film is thin and bonded, so force does not lift it, and pressure will dent thin aluminum gutter stock, drive water behind the gutter onto the fascia, and pull hangers out of alignment. The correct approach is a dedicated cleaner with dwell time and a soft brush.
How do I clean the outside of my gutters?
Wet the surface, apply a dedicated gutter cleaner to a ten to fifteen foot section, let it dwell the stated time, agitate with a soft-bristle brush on an extension pole using long horizontal strokes, then rinse thoroughly before moving on. Work in shade and repeat where needed.
Will tiger stripes come back after cleaning?
Yes. The source is asphalt shedding from the roof above, which cleaning the gutter does not change. Most homes need this repeated annually or every couple of years, and recurrence gets faster as the roof ages and sheds more heavily.
Where this is one task among many, recurring house cleaning services take the broader load.
Gutter faces are a chemistry job with a recurring cause, so the realistic goal is a clean line each year rather than a permanent fix. If reaching the run safely is the obstacle, get a quote and we will look at the roof line with you.