· by Michael Blair, Nashville's Pressure Washing
Tiger striping is the trade name for the dark vertical streaks that form on the outside face of a gutter, heaviest where water comes over the front edge. In our experience the soft wash that clears the siding leaves them behind, and a pressure rinse rarely does better. What they are made of is less settled than most cleaning advice suggests, and that is worth knowing before anyone puts a wand or a bucket of chemical on them.
What the stripes are
Most gutters are formed from painted metal, and the National Coil Coating Association’s building products page describes prepainted metal as a popular choice for gutters and downspouts. Exterior paint films can chalk as they age, leaving a fine powder at the surface, and the condition is common enough that ASTM D4214 sets out standard test methods for judging how much a white or tinted exterior paint has chalked.
The usual explanation in our trade is that rain and dew running over the lip carry that chalk along with airborne grime and runoff from the roof, then leave it in streaks where the water dries on the face. We have not found a published study that pins down the chemistry, so treat that as the working theory. What we see on the houses we wash is where the stripes sit: under the points where water comes over the edge, and often darkest on the sides of the house that stay damp longest.
Why pressure and house wash do not work
Pressure takes off what is loose. The stripes hold to the paint well enough that a rinse tends to lift the powder around them and leave them standing out more sharply than before. Turning the pressure up until they move risks taking the finish off as well, and paint lost from a gutter face is gone for good; our post on what pressure washing can permanently damage makes the same point about roofs, decks and siding.
The sodium hypochlorite mix we use for house washing is there for mildew, algae and organic grime on the siding. On gutter stripes it usually does little beyond brightening the surface around them, which is why a freshly washed house can make its gutters look worse.
What actually removes tiger stripes from gutters?
A cleaner made for the job, sold as a gutter cleaner, brightener or whitener, worked along the face with a soft brush or pad one section at a time and rinsed at low pressure. Formulas differ from one brand to the next, so the label and its safety data sheet decide the dilution, how long it can stay on and what it is safe near. We try it first on a short run at the back of the house before doing the front.
Heavy striping can take a second pass. Before we start, we wipe the gutter face with a clean cloth, which is close to how the ASTM method works: chalk is transferred to fabric or a fingertip and compared with photographic reference standards. When the cloth comes away full of color, the finish is chalking, and getting the stripes off will show a faded gutter underneath. That is the gutter’s real condition, and no cleaner changes it.
- A cleaner made for gutters, used as its label directs, not bleach and not high pressure
- Soft brush or white pad, worked along the length
- Low-pressure rinse before it dries
- Plants and painted surfaces below wetted or covered, as the product label requires
Why do gutter stripes keep coming back?
The stripes return because the paint keeps weathering and the water keeps running the same way over the lip. Doing the gutter faces with each house wash keeps it a light job instead of years of buildup at once; our guide to how often a Nashville house needs washing sets out the interval we suggest. Some companies offer a protectant coat over clean gutters to slow re-soiling. We know of no published test of how long that lasts, so ask what product it is and what results they have seen.
Overflow is the other half. In our experience the worst striping sits under gutters that spill over the front, so clear troughs, enough pitch to move water to the outlets and a drip edge that sends roof water into the gutter all help. On a gutter that leaves heavy chalk on the cloth and has striped for years, cleaning has stopped being the answer, and recoating is a question for a painter. If you would like the gutter faces looked at with your next wash, ask us for a free estimate.
Sources
- National Coil Coating Association, Building Products — Prepainted metal is a popular choice for manufacturing gutters and downspouts
- ASTM International, D4214-07(2015) Standard Test Methods for Evaluating the Degree of Chalking of Exterior Paint Films — Chalking of white or tinted exterior paint films; chalk transferred to fabric or a fingertip and compared with photographic reference standards
FAQ
Tiger Stripes on Gutters and Why Washing Fails — questions
What causes the black stripes on my gutters?
The common explanation is chalk from the weathering gutter paint, mixed with airborne grime and roof runoff and left in streaks where rain and dew dry on the face. No published study we know of settles the exact chemistry. In our experience the streaks are heaviest below the points where water comes over the edge and on the sides of the house that stay damp longest.
Will pressure washing remove tiger stripes?
Usually not. In our experience a pressure rinse lifts the loose powder around the stripes and leaves them more visible, and pressure high enough to move them risks stripping the paint. We use a cleaner made for gutters, worked in with a soft brush and rinsed at low pressure, following its label.
How do I stop gutter stripes coming back?
Clean the gutter faces with each house wash before years of buildup collect, and cut down on water spilling over the front edge with clear troughs, correct pitch and a drip edge that sends water into the gutter. A gutter whose paint chalks heavily onto a cloth may be past cleaning and ready for a painter.
How do you remove tiger stripes from gutters?
With a cleaner sold for the purpose, as a gutter cleaner, brightener or whitener, worked along the face with a soft brush or pad a section at a time and rinsed at low pressure before it dries. The label sets the dilution and dwell time, and we try it on a short run at the back first.