What are Tiger Stripes or Zebra Stripes on Gutters?
These black streaks – also known as tiger stripes or zebra stripes – are dark gray or black vertical stripes running down the front of aluminum gutters due to molecular bonding of pollutants to the aluminum.
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Why do gutters get black streaks?
Most gutters in the US are made of aluminum and the paint is applied using an anodizing process. In order to make the paint adhere to the metal they have to ionize the metal, which makes pollutants ionically bond to the gutter. The problem comes about when you mix in pollutants, rain and sun over time.
Smog, dirt and other particles from the roof it if overflows. Water hits the front of the gutter and drips down carrying smog and dirt, then it dries on the front and stains the gutter. Gets in there with materials in the gutter and overflows to the gutter. Statically bonded to the gutter.
Be careful if your gutter’s protective sealing is gone – in that case you may not be able to clean off the tiger stripes and you might be left with the option of replacing your gutters all together.
I’ve actually seen two explanations for this:
1. When rain drops hit the front of the gutter and rolls down it leaves behind pollutants from the air that are ionically bonded to the alumninum. The black material is electrostatically bonded to the gutter, so normal rinsing or washing does not get rid of them.
2. The other explanation is repeated a lot but from what I’ve read, is less likely a cause: when rain water overflows your gutters it carries asphalt from your roof shingles that bonds via a chemical reaction to the front of the aluminum gutters. I’d say the nail in the coffin for this theory is that tiger stripes can also occur on houses with non-asphalt rooves!
Note that these black stripes on your gutter might be more or less prevalent in your area depending on where you live. Things like air quality, pollutants, etc can increase the odds you’ll get them.
A few things to look out for: the way you clean a dirty/old gutter will depend on what is causing the issue. If it’s mold, algae and dirt, that’s one. If it’s tiger striping, that’s another. It could also be that the protective coating on your aluminum has worn away. In this case if your gutters are gray or dirty you may not be able to clean it back to it’s original white and you may be forced to replace them to get back to their original shine.
Will Power Washing Clean Black Streaks Off Gutters?
Most likely not. Pressure washing done for a general exterior house cleaning will not fix the gutter striping. It’s a separate thing so don’t assume if you’re getting the exterior of your house cleaned that the pressure washing company will also clean your gutters.
How do you clean black streaks off the face of gutters?
Regardless of the cause, these unsightly stripes are more than just dirt or grime and won’t come easily off with regular cleaning solutions.
Bleach won’t cut it.
Cleaners that attack algae won’t work either.
Nope. Pure pressure washing won’t either.
Now it is possible that your gutters are just dirty, so I would definitely recommend trying to clean off a section first using a more gentle gutter cleanser with water and a rag. If it’s just standard dirt, algae and grime it should clean off fairly easily, but if not then you should try cleaning off the gutters with specialized solutions that will specifically attack the zebra stripes.
Sadly, even if you do get those gutters clean the black streaks are likely to return within 1 to 3 years.
Let’s get to it:
Rag, sponge or cloth. You could also use a soft bristled brush, but don’t use a metal or hard bristled brush as that could damage the gutter.
Protection: Working with these chemicals, it would be wise to protect yourself with gloves, goggles and
Depending on what you are using to clean your gutters, it may have harmful or dangerous chemicals so be sure to read the instructions on the cleaner, but generally you would be wise to wear eye protection and gloves. If it is particularly strong, you might want to wear a mask.
Sprayer or pressure washer: if you can get up close, you can use a hand spray bottle. If not you could use a pressure washer.
Ladder. Unless you have a 1 story house, you’ll need to climb up to reach 2nd story gutters even with extended cleaning tools.
Can you lean a ladder against a ladder?
When to do it:
With many cleaners they recommend you only use them when it’s 50 degrees Fahrenheit or warmer.
Wet down the area:
In order to limit the chance of wrecking anything on your house or any plants under the gutter, wet down the area near and under the gutter.
Best cleaners for black streaks on a gutter:
Make sure you read the individual instructions for the cleaner you end up getting.
SPRAY ON, WIPE WITH A RAG: I used Ultimate Gutter Cleaner Gutter Stain Remover and it worked great. Here are the results (clean part on the left, still-dirty part on the right). It was fast and easy to use. I just made sure to spray it on and basically immediately wipe it off.
Here are the results I got right away:
See it in action here:
Here are some other options:
FOR PRESSURE WASHERS: Gutter Butter
SPRAY ON, RINSE OFF: Gutter Brite
SPRAY ON AND WIPE OFF: Streak Getter
NOTE: your gutter has to be 74 degrees fahrenheit when you apply this. That doesn’t mean the day momentarily goes above 74 degrees, it has to be warm enough, long enough for your gutter to reach that temperature before applying it.
SPRAY ON, RINSE OFF: Gutter Zap Cleaner: this is alcohol based so it will dry more quickly than others.
Dwell Time and Rinse off
Keep the area wet as you go which means you need to work in manageable sections.
Let it sit for a few minutes, but DON’T LET IT DRY. Rinse off the gutter and any surrounding plants in the area.
You could also wipe it down with a damp rag.
Remember, the sunnier, dryer and hotter it is the faster it will dry.
So get out there, clean those gutters and bump up your curb appeal!
What if you can’t get black streaks off your gutters?
If the finish on the gutters has worn off and you have general staining and the gutters are graying it might be too late. Your gutter has probably oxidized.
You can test for this if you run your hand across it and it comes away chalky. Will have to replace it because the gutter cleaner options just won’t do anything. You want to see actual stripes to be able to follow this guide to clean them off.