You have probably seen them without registering what they are. Dark vertical streaks running down the face of the gutters and along the fascia, usually worse under the roof valleys, and stubbornly unaffected by rain. They are one of the most common things we get asked about, and one of the most misunderstood.
What the streaks actually are
Those marks are not rust and they are not simply dirt. They are a mix of oxidised material washed off the roof, airborne pollutants, and bitumen residue from roofing materials, all bound together in a sticky film that adheres to the electrostatically charged surface of the gutter.
That electrostatic bond is why rain does not shift them. Rain runs over the film rather than lifting it. It also explains why the streaks form in the pattern they do, concentrated where roof runoff is heaviest and tapering out along the run of the gutter.
In the trade this is often called tiger striping, and it affects almost every roofing and gutter material used in Brisbane, painted metal included.
Why scrubbing usually fails
The instinct is to attack it with a stiff brush and household detergent. This rarely works and often makes things worse. Ordinary detergents do not break the bond, so people compensate with pressure, and pressure on a gutter face either dents the metal or drives water behind the gutter and into the fascia.
The other common mistake is an abrasive pad. It will take the streak off, along with a layer of the paint finish, leaving a dull patch that weathers differently from the rest of the gutter and looks worse from the ground than the original streaking.
What actually removes them
Tiger striping needs a purpose-made gutter cleaner that breaks the electrostatic bond, applied by hand, given time to dwell, then rinsed at low pressure. It is a slower job than most people expect because it is largely manual, done at height, working along the full run of the guttering.
Done properly, the gutters come back to their original colour. On a house where the roof and walls have already been cleaned, it is usually the difference between a job that looks nearly finished and one that looks complete.
Do it in the right order
Gutters should be cleaned after the roof and before the walls. Cleaning the roof pushes material into and over the gutters, so gutters done first get dirtied again. Walls come last because rinse water from the gutter line runs down the wall.
Getting the sequence wrong is the most common reason a house wash looks patchy afterwards. If you are booking an external house clean, it is worth asking what order the work will be done in.
We treat gutter streaking as part of a full exterior clean across Brisbane. If your gutters have gone dark and streaky, send a photo and we will tell you honestly whether it will come back or whether the paint has gone past the point of recovery.
