Post by:
Jud West
Post date: 02 Aug, 2026

Real-World Testing. Practical Engineering. Better Downstreaming Systems.

DrawMax Technical Series — Article 12

Published by DrawMax Technical Series
5-minute read

Gutter Tiger Striping: What It Is and How to Clean It

A house wash can remove algae and mildew from gutters but still leave dark streaks behind. Those streaks may be tiger striping, not leftover organic growth.

This guide explains how to spot the difference, choose a suitable cleaner, and clean the gutter face without causing unnecessary damage to the finish.

Key takeaway: If a normal wash removes the growth but leaves vertical streaks, stronger bleach may not solve the problem. You may need a different type of cleaner.

1. Identify What You Are Cleaning

What do tiger stripes look like?

Tiger stripes are dark gray, brown, or black streaks that run down the front of a gutter. They stand out most on white and light-colored aluminum gutters.

Dark vertical streaks on a white gutter face illustrate the tiger-striping pattern.

Rainwater carries dirt and other material from the roof over the gutter edge. As the surface gets wet and dries again, this buildup can stick tightly to the finish. A normal house wash may clean most of the gutter while leaving the streaks behind.

Tiger striping, organic growth, or oxidation?

These problems can look similar, and a gutter may have more than one at the same time. Check the surface before choosing a cleaner.

• Organic growth: Algae, mildew, or other growth may appear as a green or black film. A sodium hypochlorite-based wash is a common starting point.
• Tiger striping: Dark vertical streaks remain after the normal wash. A cleaner made for gutter streaks may be needed.
• Oxidation: The painted finish looks dull, faded, or chalky. This is wear in the coating, not just dirt. Test carefully and consider whether the finish needs restoration.

What does “electrostatic bonding” mean?

Contractors often use this term to describe how firmly tiger stripes stick to gutters. It does not mean the dirt is literally glued to the surface by electricity.

Roof runoff, airborne dirt, weather exposure, and the condition of the paint can all play a part. Tiger striping describes the stain pattern. Oxidation describes wear or breakdown of the finish.

2. Choose the Right Cleaner

Not every exterior-cleaning chemical is suitable for painted aluminum. Choose a product based on both the buildup you need to remove and the condition of the gutter finish.

Sodium hypochlorite (SH)

Best suited for: Organic growth, such as algae and mildew.

Sodium hypochlorite, often called SH or bleach, is commonly used in a house wash. It can remove organic growth from gutters, but tiger stripes may remain after that growth is gone.

If the streaks are not changing, do not assume that more SH is the answer. Rinse thoroughly, inspect the gutter, and decide whether a different cleaner is needed.

Gutter cleaners and brighteners

Best suited for: Tiger stripes and stubborn grime left on the gutter face after normal washing.

A product made for gutter cleaning is generally a better choice for these streaks than simply increasing the bleach strength. Examples mentioned for this type of work include:

• Gutter Butter: A professional gutter cleaner and brightener used for tiger stripes and stubborn surface buildup.
• F-13 Gutter Grenade: A professional gutter cleaner commonly used for tiger stripes and heavily soiled gutter faces.
• Gutter Zap: A gutter-cleaning product designed for black streaks and tiger-striping removal.

Follow the current instructions for the specific product. Check the mixing ratio, application method, dwell time, required protective gear, and whether it is safe for the surface. Dwell time means how long the cleaner stays on the surface before rinsing. Stronger is not always better.

3. Check the Finish and Test First

Before treating the whole gutter, look for chalking, fading, peeling paint, or other signs of a worn coating. A gentle wipe in a hidden area can help reveal a chalky finish.

Always test the cleaner on a small, hidden spot first. Older or oxidized coatings may be damaged or visibly changed by gutter-cleaning chemicals.

Cleaning can also reveal damage that was already there. Dirt may hide years of fading and wear. Once the dirt is removed, the finish may look uneven.

Strong chemicals, long dwell times, and hard scrubbing can make this more noticeable. Use the test spot to set realistic expectations before starting the full job.

4. Follow This Cleaning Process

1. Wash the gutter first. Use your normal exterior-cleaning process to remove loose dirt, algae, mildew, and other organic growth.
2. Rinse and check the results. If the gutter is mostly clean but dark vertical streaks remain, you may be dealing with tiger striping.
3. Inspect the coating. Look for fading, chalking, peeling paint, and other wear. Do not mistake a damaged finish for dirt that needs more cleaning.
4. Test a small, hidden area. Follow the cleaner’s instructions and check how the finish responds, especially on older gutters.
5. Apply the gutter cleaner. Follow the current mixing, application, and dwell-time directions. Work in small sections and do not let the cleaner dry on the surface.
6. Gently scrub if needed. Use a soft brush, microfiber applicator, or another tool that is safe for the surface. Let the cleaner do most of the work.
7. Rinse thoroughly. Completely rinse the gutter and nearby surfaces.
8. Check before repeating. Decide whether you are seeing leftover buildup, oxidation, permanent staining, or damage to the coating before applying more cleaner.

Why light scrubbing may help

Tiger-stripe removal is not always a touch-free process. Gentle scrubbing, also called agitation, can help loosen stubborn buildup after the cleaner is applied.

Avoid aggressive scrubbing. It can change or damage a finish that is already worn or oxidized.

The Contractor Takeaway

When streaks remain after a house wash, first identify what is left:

• Organic growth: An SH-based cleaning process may be suitable.
• Tiger stripes or stubborn grime: Consider a gutter cleaner or brightener made for that job.
• A chalky or worn finish: Use caution, test first, and decide whether restoration is needed.

The goal is not to use the strongest chemical. It is to choose the right cleaner for the problem and remove the buildup without unnecessarily damaging the gutter finish.

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Continue Learning with the DrawMax Technical Series

This is Article 12 in a growing library built to help contractors understand better downstreaming and exterior-cleaning practices. 

Related Articles in This Series

• Article 5: Choosing the Correct Injector for Your Machine
• Article 7: Building a Complete Downstreaming System
• Article 9: Troubleshooting Common Downstreaming Problems
• Article 11: Flow-Sensitive vs. Pressure-Trapped Unloaders

About the DrawMax Technical Series

The DrawMax Technical Series helps pressure washing contractors understand the science behind downstreaming. Our articles draw on practical engineering, field testing, and real-world experience, not marketing hype. Our goal is simple: share clear information that helps contractors build more efficient, dependable downstreaming systems.

Technical note: Product formulas and instructions can change. Always read the current product label and Safety Data Sheet (SDS) before use.