Tiger stripes: the black streaks down your gutter face
Those black stripes are road film — exhaust and brake-dust particulates plus leaf tannins — electrostatically bonded to the paint where water sheets over the drip edge. Rain deposits them; it cannot remove them. Shifting them takes detergent, soft agitation and a fresh-water rinse. Schmick does it as part of a gutter clean: from $180, with most single-storey homes landing between $220 and $430.
The stripes are bonded on, not sitting there
Look at where the streaks sit. They run vertically down the gutter face, always in the same tracks, usually below a join or a low point in the run. That is water finding its exits. When the gutter overtops or wicks over the drip edge, it carries whatever is inside — tannins leached from leaf litter, plus the film of road grime that settles on every Sydney roof. The water evaporates. The load stays.
The reason the stripes laugh at rain is electrostatic bonding. The particulates in road film — brake dust, exhaust soot, general urban fallout — carry a charge, and they bond to the painted steel rather than resting on it. Each wetting dissolves a little more tannin, deposits it in the same track, and dries. The streak darkens layer by layer. By the time you notice it from the street, it is chemically attached to the paint, not perched on top of it.
Rain applies them; it never removes them
It is tempting to wait for a good downpour to tidy the gutter line. The downpour is what put the streaks there. Rain refills the gutter, stirs the tannin soup inside, and sends a fresh coat over the same drip points. Then the sun dries it and the residue concentrates. A wet winter does not wash your gutter face — it repaints it, one storm at a time.
BlueScope, the maker of Colorbond steel, is blunt about this in its TB-4 maintenance bulletin: coated steel needs regular fresh-water washing, and more often near marine environments. That describes most of Schmick's patch. The North Shore, the Eastern Suburbs and Manly all sit inside salt-air range of the harbour or the ocean, which means the washing BlueScope specifies is not optional housekeeping. It is the condition the coating was designed around.
Detergent and agitation — and what they cannot fix
The fix is chemistry plus contact. A mild detergent breaks the bond between the particulate film and the paint. A soft brush or pad supplies the agitation the streak actually needs. A fresh-water rinse carries it off. The sequence matters. Detergent without agitation smears the film. Agitation without detergent grinds it in. And a pressure washer aimed at a gutter face is exactly the harsh treatment BlueScope's bulletin warns against — it can scar the coating the streaks were sitting on.
One honest caveat. Washing removes what is on the paint, not what has happened to it. A gutter face that has spent fifteen years in full sun may be chalked — the surface oxidised to a dull powder. Cleaning will take the black stripes off a chalked gutter, and the improvement is real, but the colour underneath will read faded, because it is. No wash restores paint. If the streaks lift and the face still looks tired, that is a repaint conversation, and we will say so.
A firm number beats a guess
Schmick treats the gutter face as part of the gutter clean, not an extra. The interior gets cleared and flushed; the face gets detergent, agitation and a rinse on the same visit. Gutter cleaning starts at $180, most single-storey homes land between $220 and $430 depending on gutter length, and two storeys adds about 50 per cent. If the rest of the exterior is due at the same time, bundling services on one visit saves 5 to 15 per cent.
You do not need someone standing in your driveway to price it. Answer a few questions about the house in the instant quote and it returns a firm, bookable number in about 60 seconds — and that number holds unless the place is materially different from what you described. The tiger stripes took years to build. Finding out what they cost to remove takes a minute.